


Spring HelloWorld Example Using Eclipse and Maven

Microservices with Spring
ENGINEERING
Introduction
NOTE: Revised June 2018
A simple example of setting up a microservices system using Spring, Spring Boot and Spring Cloud.
Microservices allow large systems to be built up from a number of collaborating components. It does at the process level what Spring has always done at the component level: loosely coupled processes instead of loosely coupled components.
For example imagine an online shop with separate microservices for user-accounts, product-catalog order-processing and shopping carts:
Inevitably there are a number of moving parts that you have to setup and configure to build such a system. How to get them working together is not obvious – you need to have good familiarity with Spring Boot since Spring Cloud leverages it heavily, several Netflix or other OSS projects are required and, of course, there is some Spring configuration “magic”!
In this article I aim to clarify how things work by building the simplest possible system step-by-step. Therefore, I will only implement a small part of the big system – the user account service.
The Web-Application will make requests to the Account-Servicemicroservice using a RESTful API. We will also need to add a discovery service – so the other processes can find each other.
The code for this application is here: https://github.com/paulc4/microservices-demo.
The description of how it works is deliberately detailed. Impatient readers may prefer to simply look at the code. Note that it contains three microservices in a single project.
Follow-Up 1: Other Resources
This article only discusses a minimal system. For more information, you might like to read Josh Long’s blog article Microservice Registration and Discovery with Spring Cloud and Netflix’s Eureka which shows running a complete microservice system on Cloud Foundry.
The Spring Cloud projects are here.
Follow Up 2: SpringOne Platform 2018
Book your place at SpringOne2 Platform in Washington DC, USA this September – simply the best opportunity to find out first hand all that’s going on and to provide direct feedback. The name has changed, from Spring One, to reflect the growth of Spring in platform services (such as the Spring Cloud projects).
Updates (June 2018)
A number of changes since I originally wrote this blog:
- A discussion of using multiple instances of the same service on the same host.. Demo application updated to match.
- A discussion of
@LoadBalanced
– how this works has changed since the Brixton release-train (Spring Cloud 1.1.0.RELEASE). - Refactored configuration of Accounts microservice into its own class
AccountsConfiguration
. - Upgraded to Spring Boot 2, so a few Boot classes have changed package.
- Upgraded demo application to Spring Cloud Finchley release-train (including various fixes from the comments at the end – thanks for the feedback).
- The Eureka server dependency has changed to
spring-cloud-starter-netflix-eureka-server
.
Previous version, using Spring Boot 1.5.10 and Spring Cloud Edgeware SR3, is available as git tag v1.2.0.
OK, let’s get started …
Service Registration
When you have multiple processes working together they need to find each other. If you have ever used Java’s RMI mechanism you may recall that it relied on a central registry so that RMI processes could find each other. Microservices has the same requirement.
The developers at Netflix had this problem when building their systems and created a registration server called Eureka (“I have found it” in Greek). Fortunately for us, they made their discovery server open-source and Spring has incorporated into Spring Cloud, making it even easier to run up a Eureka server. Here is the complete discovery-server application:
@SpringBootApplication
@EnableEurekaServer
public class ServiceRegistrationServer {
public static void main(String[] args) {
// Tell Boot to look for registration-server.yml
System.setProperty("spring.config.name", "registration-server");
SpringApplication.run(ServiceRegistrationServer.class, args);
}
}
It really is that simple!
Spring Cloud is built on Spring Boot and utilizes parent and starter POMs. The important parts of the POM are:
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.0.1.RELEASE</version>
</parent>
<dependencies>
<dependency>
<!-- Setup Spring Boot -->
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
</dependency>
<dependency>
<!-- Setup Spring MVC & REST, use Embedded Tomcat -->
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<!-- Spring Cloud starter -->
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter</artifactId>
</dependency>
<dependency>
<!-- Eureka for service registration -->
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-eureka-server</artifactId>
</dependency>
</dependencies>
<!-- Spring Cloud dependencies -->
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-dependencies</artifactId>
<version>Finchley.RELEASE</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
This POM has changed since I originally wrote the article to use Spring Boot as its parent not Spring Cloud. Spring Cloud dependencies are provided via the dependency management section.
An sample gradle build file is also included in the github code.
Note: Finchley.RELEASE is the current “release train” – a set of co-ordinated releases — see note on Spring Cloud home page.
By default Spring Boot applications look for an application.properties
or application.yml
file for configuration. By setting the spring.config.name
property we can tell Spring Boot to look for a different file – useful if you have multiple Spring Boot applications in the same project – as I will do shortly.
This application looks for registration-server.properties
or registration-server.yml
. Here is the relevant configuration from registration-server.yml
:
# Configure this Discovery Server
eureka:
instance:
hostname: localhost
client: # Not a client, don't register with yourself (unless running
# multiple discovery servers for redundancy)
registerWithEureka: false
fetchRegistry: false
server:
port: 1111 # HTTP (Tomcat) port
By default Eureka runs on port 8761, but here we will use port 1111
instead. Also by including the registration code in my process I might be a server or a client. The configuration specifies that I am not a client and stops the server process trying to register with itself.
Using Consul
Spring Cloud also supports Consul as an alternative to Eureka. You start the Consul Agent (its registration server) using a script and then clients use it to find their microservices. For details, see this blog article or project home page.
Try running the RegistrationServer now (see below for help on running the application). You can open the Eureka dashboard here: http://localhost:1111 and the section showing Applications will be empty.
From now on we will refer to the discovery-server since it could be Eureka or Consul (see side panel).
Creating a Microservice: Account-Service
A microservice is a stand-alone process that handles a well-defined requirement.
When configuring applications with Spring we emphasize Loose Coupling and Tight Cohesion, These are not new concepts (Larry Constantine is credited with first defining these in the late 1960s – reference) but now we are applying them, not to interacting components (Spring Beans), but to interacting processes.
In this example, I have a simple Account management microservice that uses Spring Data to implement a JPA AccountRepository
and Spring REST to provide a RESTful interface to account information. In most respects this is a straightforward Spring Boot application.
What makes it special is that it registers itself with the discovery-server at start-up. Here is the Spring Boot startup class:
@EnableAutoConfiguration
@EnableDiscoveryClient
@Import(AccountsWebApplication.class)
public class AccountsServer {
@Autowired
AccountRepository accountRepository;
public static void main(String[] args) {
// Will configure using accounts-server.yml
System.setProperty("spring.config.name", "accounts-server");
SpringApplication.run(AccountsServer.class, args);
}
}
The annotations do the work:
@EnableAutoConfiguration
– defines this as a Spring Boot application.@EnableDiscoveryClient
– this enables service registration and discovery. In this case, this process registers itself with the discovery-server service using its application name (see below).@Import(AccountsWebApplication.class)
– this Java Configuration class sets up everything else (see below for more details).
What makes this a microservice is the registration with the discovery-server via @EnableDiscoveryClient
and its YML configuration completes the setup:
# Spring properties
spring:
application:
name: accounts-service
# Discovery Server Access
eureka:
client:
serviceUrl:
defaultZone: http://localhost:1111/eureka/
# HTTP Server
server:
port: 2222 # HTTP (Tomcat) port
Note that this file
- Sets the application name as
accounts-service
. This service registers under this name and can also be accessed by this name – see below. - Specifies a custom port to listen on (2222). All my processes are using Tomcat, they can’t all listen on port 8080.
- The URL of the Eureka Service process – from the previous section.
Run the AccountsServiceapplication now and let it finish initializing. Refresh the dashboard http://localhost:1111 and you should see the ACCOUNTS-SERVICE listed under Applications. Registration takes up to 30 seconds (by default) so be patient – check the log output from RegistrationService
Warning: Do not try to display XML output using the internal web-viewer of Eclipse/STS because it cannot do so. Use your favorite web browser instead.
For more detail, go here: http://localhost:1111/eureka/apps/ and you should see something like this:
<applications>
<versions__delta>1</versions__delta>
<apps__hashcode>UP_1_</apps__hashcode>
<application>
<name>ACCOUNTS-SERVICE</name>
<instance>
<hostName>autgchapmp1m1.corp.emc.com</hostName>
<app>ACCOUNTS-SERVICE</app>
<ipAddr>172.16.84.1</ipAddr><status>UP</status>
<overriddenstatus>UNKNOWN</overriddenstatus>
<port enabled="true">3344</port>
<securePort enabled="false">443</securePort>
...
</instance>
</application>
</applications>
Alternatively go to http://localhost:1111/eureka/apps/ACCOUNTS-SERVICE and see just the details for AccountsService – if it’s not registered you will get a 404.
Configuration Options
Registration Time: Registration takes up to 30s because that is the default client refresh time. You can change this by setting the eureka.instance.leaseRenewalIntervalInSeconds
property to a smaller number (in the demo application I have set it to 5). This is not recommended in production. See also.
eureka:
instance:
leaseRenewalIntervalInSeconds: 5 # DO NOT DO THIS IN PRODUCTION
Registration Id: A process (microservice) registers with the discovery-service using a unique id. If another process registers with the same id, it is treated as a restart (for example some sort of failover or recovery) and the first process registration is discarded. This gives us the fault-tolerant system we desire.
To run multiple instances of the same process (for load-balancing and resilience) they need to register with a unique id. When I first wrote this blog, that was automatic and since the Brixton release-train, it is again.
Under the Angel release train, the instance-id, used by a client to register with a discovery server, was derived from the client’s service name (the same as the Spring application name) and also the client’s host name. The same processes running on the same host would therefore have the same id, so only one could ever register.
Fortunately you could set the id property manually via the client’s Eureka metadata map, like this:
eureka:
instance:
metadataMap:
instanceId: ${spring.application.name}:${spring.application.instance_id:${server.port}}
Since the Brixton release train, this is now the default. So what does it do?
We are setting the instanceId
to application-name:instance_id
, but if instance_id
is not defined, we will use application-name::server-port
instead. Note that the spring.application.instance_id
is only set when using Cloud Foundry but it conveniently provides a unique id number for each instance of the same application. We can do something similar when running elsewhere by using the server-port (since different instances on the same machine must listen on different ports. Another example you will often see is ${spring.application.name}:${spring.application.instance_id:${random.value}}
but I personally find using the port number makes each instance easy to identify – the random values are just long strings that don’t mean anything.
Note: The syntax ${x:${y}}
is Spring property shorthand for ${x} != null ? ${x} : ${y}
.
Since the Brixton release there is also a dedicated property for this:
eureka:
instance:
instanceId: ${spring.application.name}:${spring.application.instance_id:${random.value}}
Accessing the Microservice: Web-Service
To consume a RESTful service, Spring provides the RestTemplate
class. This allows you to send HTTP requests to a RESTful server and fetch data in a number of formats – such as JSON and XML.
Note: The Accounts microservice provides a RESTful interface over HTTP, but any suitable protocol could be used. Messaging using AMQP or JMS is an obvious alternative (in which case the Discovery Server is no longer needed – instead processes need to know the names of the queues to talk to, consider using the Spring Cloud Configuration Server for this).
Which formats can be used depends on the presence of marshaling classes on the classpath – for example JAXB is always detected since it is a standard part of Java. JSON is supported if Jackson jars are present in the classpath.
A microservice (discovery) client can use a RestTemplate
and Spring will automatically configure it to be microservice aware (more of this in a moment).
Encapsulating Microservice Access
Here is part of the WebAccountService
for my client application:
@Service
public class WebAccountsService {
@Autowired // NO LONGER auto-created by Spring Cloud (see below)
@LoadBalanced // Explicitly request the load-balanced template
// with Ribbon built-in
protected RestTemplate restTemplate;
protected String serviceUrl;
public WebAccountsService(String serviceUrl) {
this.serviceUrl = serviceUrl.startsWith("http") ?
serviceUrl : "http://" + serviceUrl;
}
public Account getByNumber(String accountNumber) {
Account account = restTemplate.getForObject(serviceUrl
+ "/accounts/{number}", Account.class, accountNumber);
if (account == null)
throw new AccountNotFoundException(accountNumber);
else
return account;
}
...
}
Note that my WebAccountService
is just a wrapper for the RestTemplate fetching data from the microservice. The interesting parts are the serviceUrl
and the RestTemplate
.
Accessing the Microservice
As shown below, the serviceUrl
is provided by the main program to the WebAccountController
(which in turn passes it to the WebAccountService
):
@SpringBootApplication
@EnableDiscoveryClient
@ComponentScan(useDefaultFilters=false) // Disable component scanner
public class WebServer {
// Case insensitive: could also use: http://accounts-service
public static final String ACCOUNTS_SERVICE_URL
= "http://ACCOUNTS-SERVICE";
public static void main(String[] args) {
// Will configure using web-server.yml
System.setProperty("spring.config.name", "web-server");
SpringApplication.run(WebServer.class, args);
}
@LoadBalanced // Make sure to create the load-balanced template
@Bean
RestTemplate restTemplate() {
return new RestTemplate();
}
/**
* Account service calls microservice internally using provided URL.
*/
@Bean
public WebAccountsService accountsService() {
return new WebAccountsService(ACCOUNTS_SERVICE_URL);
}
@Bean
public WebAccountsController accountsController() {
return new WebAccountsController
(accountsService()); // plug in account-service
}
}
A few points to note:
- The
WebController
is a typical Spring MVC view-based controller returning HTML. The application uses Thymeleaf as the view-technology (for generating dynamic HTML) WebServer
is also a@EnableDiscoveryClient
but in this case as well as registering itself with the discovery-server (which is not necessary since it offers no services of its own) it uses Eureka to locate the account service.- The default component-scanner setup inherited from Spring Boot looks for
@Component
classes and, in this case, finds myWebAccountController
and tries to create it. However, I want to create it myself, so I disable the scanner like this@ComponentScan(useDefaultFilters=false)
. - The service-url I am passing to the
WebAccountController
is the name the service used to register itself with the discovery-server – by default this is the same as thespring.application.name
for the process which isaccount-service
– seeaccount-service.yml
above. The use of upper-case is not required but it does help emphasize that ACCOUNTS-SERVICE is a logical host (that will be obtained via discovery) not an actual host.
Load Balanced RestTemplate
The RestTemplate
bean will be intercepted and auto-configured by Spring Cloud (due to the @LoadBalanced
annotation) to use a custom HttpRequestClient
that uses Netflix Ribbon to do the microservice lookup. Ribbon is also a load-balancer so if you have multiple instances of a service available, it picks one for you. (Neither Eureka nor Consul on their own perform load-balancing so we use Ribbon to do it instead).
Note: From the Brixton Release Train (Spring Cloud 1.1.0.RELEASE), the RestTemplate is no longer created automatically. Originally it was created for you, which caused confusion and potential conflicts (sometimes Spring can be too helpful!).
Note that this instance is qualified using @LoadBalanced
. (The annotation is itself annotated with @Qualifier
– see here for details). Thus if you have more than one RestTemplate bean, you can make sure to inject the right one, like this:
@Autowired
@LoadBalanced // Make sure to inject the load-balanced template
protected RestTemplate restTemplate;
If you look in the RibbonClientHttpRequestFactory you will see this code:
String serviceId = originalUri.getHost();
ServiceInstance instance =
loadBalancer.choose(serviceId); // loadBalancer uses Ribbon
... if instance non-null (service exists) ...
URI uri = loadBalancer.reconstructURI(instance, originalUri);
The loadBalancer
takes the logical service-name (as registered with the discovery-server) and converts it to the actual hostname of the chosen microservice.
A RestTemplate
instance is thread-safe and can be used to access any number of services in different parts of your application (for example, I might have a CustomerService
wrapping the same RestTemplate
instance accessing a customer data microservice).
Configuration
Below the relevant configuration from web-server.yml
. It is used to:
- Set the application name
- Define the URL for accessing the discovery server
- Set the Tomcat port to 3333
# Spring Properties
spring:
application:
name: web-service
# Discovery Server Access
eureka:
client:
serviceUrl:
defaultZone: http://localhost:1111/eureka/
# HTTP Server
server:
port: 3333 # HTTP (Tomcat) port
How to Run the Demo
A small demo of this system is at http://github.com/paulc4/microservices-demo. Clone it and either load into your favorite IDE or use maven directly. Suggestions on how to run the demo are included in the README on the project homepage.
Extra Notes
Some notes about Spring Boot usage by these applications. If you are not familiar with Spring Boot, this explains some of the “magic”!
View Templating Engines
The Eureka dashboard (inside RegistrationServer
) is implemented using FreeMarker templates but the other two applications use Thymeleaf. To make sure each uses the right view engine, there is extra configuration in each YML file.
This is at the end of registration-server.yml
to disable Thymeleaf.
...
# Discovery Server Dashboard uses FreeMarker. Don't want Thymeleaf templates
spring:
thymeleaf:
enabled: false # Disable Thymeleaf spring:
Since both AccountService
and WebService
use thymeleaf, we also need to point each at their own templates. Here is part of account-server.yml
:
# Spring properties
spring:
application:
name: accounts-service # Service registers under this name
freemarker:
enabled: false # Ignore Eureka dashboard FreeMarker templates
thymeleaf:
cache: false # Allow Thymeleaf templates to be reloaded at runtime
prefix: classpath:/accounts-server/templates/
# Template location for this application only
...
web-server.yml
is similar but its templates are defined by
prefix: classpath:/web-server/templates/
Note the / on the end of each spring.thymeleaf.prefix
classpath – this is crucial.
Command-Line Execution
The jar is compiled to automatically run io.pivotal.microservices.services.Main
when invoked from the command-line – see Main.java.
The Spring Boot option to set the start-class
can be seen in the POM:
<properties>
<!-- Stand-alone RESTFul application for testing only -->
<start-class>io.pivotal.microservices.services.Main</start-class>
</properties>
AccountsConfiguration class
@SpringBootApplication
@EntityScan("io.pivotal.microservices.accounts")
@EnableJpaRepositories("io.pivotal.microservices.accounts")
@PropertySource("classpath:db-config.properties")
public class AccountsWebApplication {
...
}
This is the main configuration class for AccountService which is a classic Spring Boot application using Spring Data. The annotations do most of the work:
@SpringBootApplication
– defines this as a Spring Boot application. This convenient annotation combines@EnableAutoConfiguration
,@Configuration
and@ComponentScan
(which, by default, causes Spring to search the package containing this class, and its sub-packages, for components – potential Spring Beans:AccountController
andAccountRepository
) .@EntityScan("io.pivotal.microservices.accounts")
– because I am using JPA, I need to specify where the@Entity
classes are. Normally this is an option you specify in JPA’spersistence.xml
or when creating aLocalContainerEntityManagerFactoryBean
. Spring Boot will create this factory-bean for me because thespring-boot-starter-data-jpa
dependency is on the class path. So an alternative way of specifying where to find the@Entity
classes is by using@EntityScan
. This will findAccount
.@EnableJpaRepositories("io.pivotal.microservices.accounts")
– look for classes extending Spring Data’sRepository
marker interface and automatically implement them using JPA – see Spring Data JPA.@PropertySource("classpath:db-config.properties")
– properties to configure myDataSource
– see db-config.properties.
Configuring Properties
As mentioned above, Spring Boot applications look for either application.properties
or application.yml
to configure themselves. Since all three servers used in this application are in the same project, they would automatically use the same configuration.
To avoid that, each specifies an alternative file by setting the spring.config.name
property.
For example here is part of WebServer.java
.
public static void main(String[] args) {
// Tell server to look for web-server.properties or web-server.yml
System.setProperty("spring.config.name", "web-server");
SpringApplication.run(WebServer.class, args);
}
At runtime, the application will find and use web-server.yml
in src/main/resources
.
Logging
Spring Boot sets up INFO level logging for Spring by default. Since we need to examine the logs for evidence of our microservices working, I have raised the level to WARN to reduce the amount of logging.
To do this, the logging level would need to be specified in each of the xxxx-server.yml
configuration files. This is usually the best place to define them as logging properties cannotbe specified in property files (logging has already been initialized before @PropertySource directives are processed). There is a note on this in the Spring Boot manual, but it’s easy to miss.
Rather than duplicate the logging configuration in each YAML file, I instead opted to put it in the logback configuration file, since Spring Boot uses logback – see src/main/resources/logback.xml. All three services will share the same logback.xml
.
Source: https://spring.io/blog/2015/07/14/microservices-with-spring
*************************************************************************************************************************************************
Microservices Implementation in Java
Feb 27, 2018
Microservices is a synonym for Service Oriented Architectural (SOA) style of constructing aggregation of many small loosely coupled services. When developing microservices with java, you can use several microservices framework. Some of the frameworks are Spring Boot, Jersey, Dropwizard, Play Framework, and Restlet. In this document, we will implement a microservice “authenticate” with Spring Boot. Spring Boot is the best and most used Microservice framework since long.
The advantage of Spring Boot is that it has a vast infrastructure and has many spring projects working along. To create microservices with Spring Boot, you need to follow below mentioned 3 steps:
- Setup new service
- Expose the resource using RestController
- Consume the service resource with RestTemplate
Here, we are going to create 3 different microservices. First microservice is Discovery Server which is a Eureka server. Second microservice is Authentication Service which is Producer service and Third microservice is Consumer service which is discovery client. This microservice can find other microservices using its RestTemplate. Let’s start with developing these three microservices.
Developing Discovery Server
Service Discovery is used so that microservices can find each other. We use Eureka for our service discovery. Eureka, created by Netflix, provides service discovery with Spring Cloud. Folder Structure for Discovery server is as below:Maven Dependency:
<parent> <groupid>org.springframework.boot</groupid> <artifactid>spring-boot-starter-parent</artifactid> <version>1.5.3.RELEASE</version> </parent> <dependencies> <dependency> <groupid>org.springframework.cloud</groupid> <artifactid>spring-cloud-starter</artifactid> </dependency> <dependency> <!-- Eureka registration server --> <groupid>org.springframework.cloud</groupid> <artifactid>spring-cloud-starter-eureka-server</artifactid> </dependency> <dependency> <groupid>org.springframework.boot</groupid> <artifactid>spring-boot-starter-web</artifactid> </dependency> </dependencies> <dependencymanagement> <dependencies> <dependency> <groupid>org.springframework.cloud</groupid> <artifactid>spring-cloud-dependencies</artifactid> <version>Camden.SR5</version> <type>pom</type> <scope>import</scope> </dependency> </dependencies> </dependencymanagement> |
Application.yml:
eureka: # Configure this Discovery Server instance: hostname: localhost client: registerWithEureka: false fetchRegistry: false server: # HTTP (Tomcat) port port: 9000 |
To run Eureka registry service is easy, just define @EnableEurekaServer annotation to spring boot application.
@SpringBootApplication @EnableEurekaServer public class DiscoveryServerApplication { public static void main(String[] args) { SpringApplication.run(DiscoveryServerApplication.class, args); } } |
After running this microservice, following output is available on localhost:9000: Here in the application section of the image, there is no instance currently available with Eureka. After running Producer and Consumer microservice, we will able to see the instances in the Application section.
Developing Authentication Service
In this, we will create Login and Registration methods. We will use Spring Data JPA for querying MySQL database using method name convention. You can learn spring data JPA from this site: https://docs.spring.io/spring-data/jpa/docs/current/reference/html/. Also in this, we will be hashing the password using Spring Security’s BCrypt algorithm. Folder Structure for Authentication service is as below:Maven Dependency:
<dependencies> <dependency> <groupid>org.springframework.cloud</groupid> <artifactid>spring-cloud-starter</artifactid> </dependency> <dependency> <groupid>org.springframework.cloud</groupid> <artifactid>spring-cloud-starter-eureka</artifactid> </dependency> <dependency> <groupid>org.springframework.boot</groupid> <artifactid>spring-boot-starter-web</artifactid> </dependency> <dependency> <groupid>org.springframework.boot</groupid> <artifactid>spring-boot-starter-data-jpa</artifactid> </dependency> <dependency> <groupid>mysql</groupid> <artifactid>mysql-connector-java</artifactid> </dependency> </dependencies> |
Application.yml:
spring: # Service registers under this name application: name: authentication-service datasource: # MySql credentials url: jdbc:mysql://127.0.0.1:3306/test username: root password: root jpa: # JPA support show-sql: true hibernate: ddl-auto: validate use-new-id-generator-mappings: false properties: hibernate: dialect: org.hibernate.dialect.MySQLDialect eureka: # Discovery Server Access client: serviceUrl: defaultZone: http://localhost:9000/eureka/ server: # HTTP Server (Tomcat) Port port: 9001 |
To define this microservice as Discovery Client, we need to include @EnableDiscoveryClient annotation to application.
@SpringBootApplication @EnableDiscoveryClient public class AuthenticationClientApplication { public static void main(String[] args) { SpringApplication.run(AuthenticationClientApplication.class, args); } } |
We will create AuthenticationRepository to querying the database using JPA. To expose Authentication service, we use RestController. In the controller, @CrossOrigin annotation is used to pass data or get data from cross platforms like Angular.
@RestController @CrossOrigin public class AuthenticationController { @Autowired private AuthenticationRepository repo; @RequestMapping("/api/getUsers") public @ResponseBody List<userauthenticationbean> getUsers() { return repo.findAll(); } @RequestMapping(value = "/api/addUser",method = RequestMethod.POST) public @ResponseBody UserAuthenticationBean addStudent(@RequestBody UserAuthenticationBean user) { // Hashing the password using BCrypt of Spring Security String hashed_password = BCrypt.hashpw( user.getPassword(), BCrypt.gensalt(12) ); UserAuthenticationBean newuser = new UserAuthenticationBean(); newuser.setUserName(user.getUserName()); newuser.setPassword(hashed_password); return repo.save(newuser); } @RequestMapping(value = "/api/getUser" ,method = RequestMethod.POST) public @ResponseBody UserAuthenticationBean getByUser(@RequestBody UserAuthenticationBean user) { UserAuthenticationBean userget = repo.findByUserName(user.getUserName()); // Comparing Hashed password with given password If ( BCrypt.checkpw( user.getPassword(), userget.getPassword() ) ){ return userget; } return null; } } </userauthenticationbean> |
After running this microservice, you can fire rest call to this service on localhost:9001. Also, instance of this service gets registered in eureka server which is already running on localhost:9000.
Developing Consumer Service
In this service, we will use RestTemplate to consume the remote service resource. Also we use Spring Cloud’s Netflix support for load balancing. Load balancing is used to decide which service instance to use. Netflix Ribbon provides several algorithms for client-side load balancing. Folder Structure for Consumer service is as below:Maven Dependency:
<dependencies> <dependency> <groupid>org.springframework.cloud</groupid> <artifactid>spring-cloud-starter-eureka</artifactid> </dependency> <dependency> <!-- Netflix Ribbon used for Load Balancing --> <groupid>org.springframework.cloud</groupid> <artifactid>spring-cloud-starter-ribbon</artifactid> </dependency> <dependency> <groupid>org.springframework.boot</groupid> <artifactid>spring-boot-starter-web</artifactid> </dependency> </dependencies> |
Application.yml:
spring: # Service registers under this name application: name: consumer-service eureka: # Discovery Server Access client: serviceUrl: defaultZone: http://localhost:9000/eureka/ server: # HTTP Server (Tomcat) Port port: 8081 |
You need to include RemoteRepository bean and RestTemplate bean in main application, so that this microservice can consume other microservices.
@SpringBootApplication @EnableDiscoveryClient public class ConsumerServiceApplication { public static final String AUTHENTICATION_SERVICE_URL = "http://AUTHENTICATION-SERVICE"; public static void main(String[] args) { SpringApplication.run(ConsumerServiceApplication.class, args); } @Bean @LoadBalanced public RestTemplate restTemplate() { return new RestTemplate(); } @Bean public AuthenticationRepository authenticationRepository(){ return new RemoteAuthenticationRepository(AUTHENTICATION_SERVICE_URL); } } |
RemoteRepository will pass the HTTP request to the given Service URL and get the response from the remote service.
public class RemoteAuthenticationRepository implements AuthenticationRepository { @Autowired @LoadBalanced protected RestTemplate restTemplate; protected String serviceUrl; public RemoteAuthenticationRepository(String serviceUrl) { this.serviceUrl = serviceUrl.startsWith("http") ? serviceUrl : "http://" + serviceUrl; } @Override public List<userauthenticationbean> findAll() { UserAuthenticationBean[] users = restTemplate.getForObject(serviceUrl+"/api/getUsers", UserAuthenticationBean[].class); return Arrays.asList(users); } @Override public UserAuthenticationBean findByUserNameAndPassword(String userName, String password) { UserAuthenticationBean user= new UserAuthenticationBean(); user.setPassword(password); user.setUserName(userName); return restTemplate.postForObject(serviceUrl + "/api/getUser",user,UserAuthenticationBean.class); } @Override public UserAuthenticationBean save(UserAuthenticationBean user) { return restTemplate.postForObject(serviceUrl + "/api/addUser", user, UserAuthenticationBean.class); } } </userauthenticationbean> |
After running this service on localhost:8081, you can fire HTTP request from client side and request to this service will be passed to producer microservice, in our scenario Authentication service. Also, you will be able to see instance of this microservice in Eureka server on localhost:9000 as below:To summarize, we understand about using microservices with Spring Boot. Also we learned some information on Eureka server and Netflix Ribbon for discovery service and Load balancing. You can learn more about microservices with spring from site: https://spring.io/blog/2015/07/14/microservices-with-spring
Source: https://www.tatvasoft.com/blog/microservices-implementation-java/
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Java microservices architecture by example: When a monolith doesn’t work
Microservices are not something new. However, this architectural approach continues to stir up interest. It claims to be a good choice for so much needed today heavy load handling and can already boast successful implementations by such big players as Google, Netflix, Amazon, and eBay.
In this article, we’ll explore a real-life example to understand the essence of microservices, the way their inner-system communication happens and the differences this architectural approach brings to the application.
A quick introduction to microservices
A microservices architecture is a particular case of a service-oriented architecture (SOA). SOA applies to the systems built with several independently deployable modules. What sets microservices apart is the extent to which these modules are interconnected. Microservices are even more independent and tend to share as little elements as possible. Every server comprises just one certain business process and never consists of several smaller servers.
Microservices become handy when one server is not enough, which happens, for example, if a server can’t handle heavy load intended for it, or if its memory use is too high. Microservices also bring a set of additional benefits, such as easier scaling, the possibility to use multiple programming languages and technologies, and others.
However, as the architecture description may sound quite vague in words, let us demonstrate how it works with a real Java-based application example. Why Java? Java is a frequent choice for building a microservices architecture as it is a mature language tested over decades and has a multitude of microservices-favorable frameworks, such as legendary Spring, Jersey, Play, and others.
So, let’s have a look at the example based on our real project – a mobile retail application that logs a user into their profile, takes orders, and sends email notifications (order confirmation, shipping updates, etc.) – and see what happens behind the scenes.
To make microservices’ distinguishing traits more explicit, we’re going to fresh up how things go with traditionally used monoliths.
What might happen with a monolith
A monolithic architecture keeps it all simple. An app has just one server and one database. The program consistently implements all business logic step by step, moving to the next stage only after the previous one is completed. All the connections between units are inside-code calls. When the user opens it to make an order, the system checks security, logs them in, takes their order, sends an e-mail order confirmation and only after all these steps are performed, the user will see the order done, and the session will be completed.
What’s wrong?
Nothing is wrong. The application works, there are just some problems you may face:
× Complete shutdown. If one part of a business logic server doesn’t work or is overloaded, the whole application may stop as it can’t proceed with the next operational stage. Back to our example, if, for some reason, notifications cannot be sent right away, the users can’t see their order successfully finished till this part of the business logic server becomes available again.
× Complicated updates. If you want to upgrade your application (introduce new technologies, add new features), even in case of minor changes, a development team will have to rewrite pretty much of it, then stop the old version for some time (which means lost clients and orders) and introduce a new one. Moreover, the development team will have to be very careful with newly introduced changes because they may damage the whole program. Also, the new parts should be necessarily written in the language of the initial system or at least in the one compatible with it.
× Frustrating UX. As a monolith continues to develop and grow and needs to deal with higher and higher load, it turns into a big and slow application with increasingly high latency, which will keep customers away as they won’t wait and may consider buying from competitors.
To tackle high load, you could duplicate the existing business logic server to get two identical servers and spread the load between them with a dynamic balancer that will randomly forward requests to the less loaded one of them. It means that, if, initially, one server processes, let’s say, 200K queries per second, which makes it too slow, now each of them deals with 100K QPS without experiencing overload. Nevertheless, it’s not a microservices architecture yet, even though there are several servers. What is more, two other problems remained unresolved: shutdowns and problematic updates.
This compels us to seek another solution.
What changes with microservices
And here we finally turn to our microservices-based example, where we designate each independent server to perform a certain business function. Here’s how we can manage to save the day with a microservices architecture.
Step 1. Split it
We split our application into microservices and got a set of units completely independent for deployment and maintenance. In our application, 2 user profile servers, 3 order servers and a notification server perform the corresponding business functions. Each of microservices responsible for a certain business function communicates either via sync HTTP/REST or async AMQP protocols.
Step 2. Pave the ways
Splitting is only the starting point of building a microservice-oriented architecture. To make your system a success, it is more important and still even more difficult to ensure seamless communication between newly created distributed components.
First of all, we implemented a gateway. The gateway became an entry point for all clients’ requests. It takes care of authentication, security check, further routing of the request to the right server as well as of the request‘s modification or rejection. It also receives the replies from the servers and returns them to the client. The gateway service exempts the client side from storing addresses of all the servers and makes them independently deployable and scalable. We also set the Zuul 2 framework for our gateway service so that the application could leverage the benefits of non-blocking HTTP calls.
Secondly, we’ve implemented the Eureka server as our server discovery that keeps a list of utilized user profile and order servers to help them discover each other. We also backed it up with the Ribbon load-balancer to ensure the optimal use of the scaled user profile servers.
The introduction of the Hystrix library helped to ensure stronger fault tolerance and responsiveness of our system isolating the point of access to a crashed server. It prevents requests from going into the void in case the server is down and gives time to the overloaded one to recover and resume its work.
We also have a message broker (RabbitMQ) as an intermediary between the notification server and the rest of the servers to allow async messaging in-between. As a result, we don’t have to wait for a positive response from the notification server to proceed with work and have email notifications sent independently.
Let’s now review the monolith problems we could come across and see what happens with them in our microservices-based application:
Complete shutdown
- If one server goes slow because of overload or crashes completely, the life won’t stop and, often, the user won’t even notice any braking. The system will either re-route the requests to its substitutes (as we have 2 user profile servers and 3 order servers) or proceed with its work and resume the function as soon as the server is recovered (in case of our notification server crashes). Maybe the client won’t get notifications right away, but at least they won’t have to look at the ‘pre-loader’ for ages.
Complicated updates
- Now we can easily update what we need. As the units are completely independent, we just re-write the needed servers to add some new features (recommendation engine, fraud detection, etc.). In our example, to introduce an IP tracker and report suspicious behavior (as Gmail does), we create fraud detection server and slightly modify our user profile servers while the rest of the servers safely stays intact.
Frustrating UX
- Loosely coupled nature of our microservices architecture and its incredible potential for scaling allows tackling incidents with minimal negative effect on user experience. For example, when we see that some of our core features run slow, we can scale the number of servers handling it (as we did from the start with user profile and order servers) or let them go a little slow for a while, if the features are not vital (as we did with notifications). In some other cases, it makes sense to skip them at all in peak times (as it happens with pop-ups that, for a while, show only textual description with no image included).
In closing
The real-life example proves that, though not magic, microservices can definitely help when it comes to creating complex applications that deal with huge loads and need continuous improvement and scaling. However, like any other architectural approach, they are not entirely flawless, so figure out whether the above-mentioned traits are actually relevant to your future application, carefully sum up all pros and cons and get professional advice, because the ‘splitting-for-splitting’ may not only turn out to be useless but also have negative effects on your application.
Source: https://www.scnsoft.com/blog/java-microservices-example

Spring Boot and WordPress CMS Integration
https://kamranzafar.org/2016/08/08/spring-boot-and-wordpress-integration/
There are a lot of excellent open source content management systems available today, WordPress being one of them, which is widely used. WordPress is a PHP based CMS so not a lot of cohesion is available with other technologies like Java, and is simply ignored as a viable content management option just for being non-Java.
In this post I will demonstrate how WordPress can be integrated with Spring Boot applications, all made possible with WordPress REST plugin and a Spring client. Both of these are open source and available for free. Below is a simple design diagram that explains how this integration works. This post assumes that the reader has prior knowledge of WordPress and Spring Boot.

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<dependency>
<groupId>org.kamranzafar.spring.wpapi</groupId>
<artifactId>spring-wpapi-client</artifactId>
<version>0.1</version>
</dependency>
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Below is a sample configuration we need in the application.properties file, so that we can connect our Spring Boot application to our WordPress site.
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wpapi.host=yoursite.com
wpapi.port=443 # Optional, default is 80
wpapi.https=true # Optional, default is false
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The Spring WP-API client needs the RestTemplate so lets create a bean in our Application and autowire the Spring client. We also need to add component scan annotation so that Spring finds and autowires all the required dependencies.
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@SpringBootApplication
@ComponentScan(“org.kamranzafar.spring.wpapi”)
public class Application implements CommandLineRunner {
public static void main(String args[]) {
SpringApplication.run(Application.class);
}
@Autowired
private WpApiClient wpApiClient;
@Bean
public RestTemplate restTemplate() {
return new RestTemplate();
}
}
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Now our spring boot application is all setup to connect to out WordPress site in order to retrieve and create content. So lets try and lookup all the posts having the keyword “Spring”, below is how we can do this.
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Map<String, String> params = new HashMap<>();
params.put(“search”, “Spring”);
params.put(“per_page”, “2”); // results per page
params.put(“page”, “1”); // current page
// See WP-API Documentation more parameters
// http://v2.wp-api.org/reference/
Post[] posts = wpApiClient.getPostService().getAll(params);
for (Post p : posts) {
log.info(“Post: “ + p.getId());
log.info(“” + p.getContent());
}
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The complete test application is available with the Spring WP-API client on Github.
This is just a small example of how we can integrate Spring Boot and WordPress. We can take this further by properly integrating WordPress in the Spring web applications platform, e.g. by enabling Single Sign On using the CAS plugin.



How to Create Spring Boot Application Step by Step
http://www.adeveloperdiary.com/java/spring-boot/create-spring-boot-application-step-step/
How to Create Spring Boot Application Step by Step

Spring Boot had been built for Rapid Application Development. In this tutorial we will learn How to Create Spring Boot Application using some easy examples. We will also focus on How to deploy spring boot application in different application servers.
Here are the following topics that we will cover in this series:
- Create Spring Boot Application using
- start.spring.io
- Eclipse STS
- IntelliJ IDEA STS
- Run Spring Boot Application using
- Java CLI
- Eclipse/IntelliJ IDEA
- Create a Basic Spring Boot application using REST
- How to use Spring Actuator
- Deploy Spring Boot application in
- IBM Liberty Profile
- IBM Application Server 8.5
If you need an introduction of Spring Boot please find my previous post below.
Create Spring Boot Application using start.spring.io
The best way of bootstrapping Spring Boot application is by using Spring Initializr. Let’s first start by opening http//start.spring.io
.As you already know, you can use either Maven or Gradle to build, however we will use Maven in this tutorial. Click on Switch to the full Version
and you will be able to see the below screen.
Software Needed
- JDK 1.8 (You can use 1.7 or 1.6)
- Maven 3.x
Steps :
- Select
Maven Project
- If you want, change the Group/Package name. We will use
com.adeveloperdiary
- Change the Artifact to
SpringBoot
, Name will automatically change to the same - Leave the packaging to Jar, Java Version to 1.8 (Make sure you have JDK 1.8 in your local or use 1.7 )
- Either type the Dependencies or select them below. We will add
Web
andActuator
here - Click on Generate Project button to download the zip file
Now Extract the zip and you will have the following files.
Open Terminal and navigate to the above folder. Type mvn clean package
and press enter. The Build will start now.
Once the build has been completed, you will have the SpringBoot-0.0.1-SNAPSHOT.jar
created inside the target
folder.
The Size of the jar would be around 13MB
since it will have the embedded Tomcat server in it.
Create Spring Boot Application using Eclipse
We will use STS Toolkit to bootstrap when using eclipse. I am using eclipse MARS .1 version. We will first install the STS (SpringSource Tools Suite). Open Eclipse Marketplace, Type STS in Find and install the STS.
Then open Spring
perspective.
Create a New
-> Spring Starter Project
.
Enter the following details. Click Next.
Select Web
and Actuator
. Click on Next.
Click on Finish.
This should create the Spring Boot Project in Eclipse.
Create Spring Boot Application using IntelliJ IDEA
We will now use IntelliJ IDEA to create our Spring Boot Application.I recommend to use the latest version of IntelliJ. Create a New Project. Select Spring Initializr
. Click on Next.
Enter the following details. Click Next.
Select Web
and Actuator
. Click Next.
Enter the project Name and click Finish.
Your Spring Boot Project has been created now.
Run Spring Boot Application using CLI
We had created the jar file, now we will run it from Command Line by executing this line
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java –jar target/SpringBoot–0.0.1–SNAPSHOT.jar
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You should be able to see Spring Boot in the Command Line.
The server should have started and the default port number will also be displayed as below.
Run Spring Boot Application in Eclipse
Its much easier to run the Spring Boot app in eclipse. Select the project, Right Click and, move to Run As
and click on Spring Boot App
. Again, remember you need to select the project to get this option, not the pom file.
Here is the output.
Run Spring Boot Application in IntelliJ IDEA
Its probably most easy, click on the run icon.
You should be able to see the logs that the application has started.
Conclusion
Hope this Step by Step approach will help you. Next we will learn how to create RESTServices and use Actuator in Spring Boot. Later we will also learn how to deploy Spring Boot Application in IBM Liberty Profile and IBM WAS 8.5 Server.
This is the 2nd part of Getting Started with Spring Boot Series. Find all the parts here.
- An Introduction to Spring Boot
- How to Create Spring Boot Application Step by Step
- How to create RESTFul Webservices using Spring Boot
- How to deploy Spring Boot application in IBM Liberty and WAS 8.5

Step-by-step Spring Boot RESTful web services example in Java using STS
https://www.theserverside.com/video/Step-by-step-Spring-Boot-RESTful-web-services-example-in-Java
In a previous article about important RESTful principles and how to create a beautiful RESTful API, I used the example of a web service that kept track of an ongoing, global score for an online rock-paper-scissors application. In this step-by-step Spring Boot RESTful web services example, we’ll implement that scenario using the Spring Web APIs and the Eclipse based SpringSource Tool Suite (STS) as the IDE.
Review of the RESTful API
The RESTful score service will provide the following functions:
RESTful clients can find out the current number of wins, losses and ties through a GET request to the following URL:
www.mcnz.com/rps/score | GET
This invocation will return a JSON string in the following format:
{ "wins":"5", "losses":"3", "ties": "0"}
RESTful clients can update the score by invocating the same URL through a PUT invocation while also passing query parameters. Again, the program will return a JSON-based representation of the score after the update. A better design would be to use JSON as the payload, but query parameters are used here for the sake of simplicity.
www.mcnz.com/rps/score?wins=1&losses=2&ties=3 | PUT
With the RESTful API, the user cannot directly set the number of wins, losses or ties. The client can only use a POST invocation to increment values one at a time. This is not an idempotent function, so it is handled through a POST. In this case, a simple number is returned to the program as opposed to a JSON string.
You can use a simple GET invocation on the appropriate resource locator to obtain the number of wins, losses or ties:
www.mcnz.com/rps/score/wins | GET www.mcnz.com/rps/score/ties | GET www.mcnz.com/rps/score/losses | GET
This step-by-step Spring Boot RESTful web services example in Java has very few prerequisites, but it does assume that you have the SpringSource Tool Suite (STS) installed. If that’s the case, you are ready to jump on the fast track to developing RESTful web services with Spring.
Step 1. Create the RESTful Spring Boot project
The first step in this exercise is to create a new Spring Boot project named restful-spring-example that uses both the Web and DevTools features. This is accomplished by kicking off the Spring Starter Project wizard in Eclipse. Select the Spring Web and DevTools options and click Finish on the Spring Boot project wizard.

Step 2: Create the Java classes
The next step is to open the restful-spring-example project and create two classes: Score.java and ScoreService.java.
Right click on the com.mcnz.restful.spring.boot package and choose to create a new class named Score. The Score class is used to keep track of the global number of wins, losses and ties that occur in the online rock-paper-scissors game. The Score class will maintain the number of wins, losses and ties as static variables of type int. State should never be held within a RESTful web service, so this class represents the externalization of state.
package com.mcnz.restful.spring.boot; public class Score { public static int WINS, LOSSES, TIES; }
After you code the Score class, create a second Java component named ScoreService. We’ll use the ScoreService class to provide access to — and the ability to manipulate — the Score. The first iteration of the class used in this Spring Boot web service example will have getter methods that return the number of wins, losses and ties, along with update methods that can increment the number of wins, losses and ties by one.

Here is the first iteration of the ScoreService class before we decorate it with RESTful annotations and subsequently configure it as a Spring Boot web service.
package com.mcnz.restful.spring.boot; /* Spring Boot web service example class */ public class ScoreService { public String updateScore(int wins, int losses, int ties) { Score.WINS = wins; Score.TIES = ties; Score.LOSSES = losses; /* to be updated to return JSON */ return this.toString(); } public int increaseWins() { return ++Score.WINS; } public int increaseTies() { return ++Score.TIES; } public int increaseLosses() { return ++Score.LOSSES; } public int getWins() { return Score.WINS; } public int getTies() { return Score.TIES; } public int getLosses() { return Score.LOSSES; } } /* End of Spring Boot web service example class. */
Step 3: Annotate the Spring Boot example class
With the first iteration of the ScoreService component coded, the next step is to transform it into a Spring Boot RESTful web service by decorating the class declaration with the @RestController annotation. The @RestController annotation informs the Spring Boot framework that the class contains methods that will be invoked through a web-based resource URL.
@RestController public class ScoreService { … }
Step 4: Annotate RESTful Spring methods
Step four is to add @RequestMapping annotations to methods. These annotations define the HTTP method used along with the structure of the resource URLs that will be used to invoke them. In the previous tutorial about how to create beautiful RESTful APIs, we established that we would invoke the update methods through a POST, and all getter methods sensibly through a GET invocation. The URLs are all resource based, so use of the URL path is /score/wins to get information about the number of wins and the path /score/ties to increase the number of ties.
Fully decorated with Spring Boot RESTful web service annotations, the next iteration of the ScoreService class looks as follows:
/* Spring Boot web service example class */ @RestController public class ScoreService { @RequestMapping(value="/score", method=RequestMethod.PUT, ) public String updateScore(int wins, int losses, int ties) { Score.WINS = wins; Score.TIES = ties; Score.LOSSES = losses; return this.toString(); /* to be updated to return JSON */ } @RequestMapping(value="/score/wins", method=RequestMethod.POST) public int increaseWins() { return ++Score.WINS; } @RequestMapping(value="/score/ties", method=RequestMethod.POST) public int increaseTies() { return ++Score.TIES; } @RequestMapping(value="/score/losses", method=RequestMethod.POST) public int increaseLosses() { return ++Score.LOSSES; } @RequestMapping(value="/score/wins", method=RequestMethod.GET) public int getWins() { return Score.WINS; } @RequestMapping(value="/score/ties", method=RequestMethod.GET) public int getTies() { return Score.TIES; } @RequestMapping(value="/score/losses", method=RequestMethod.GET) public int getLosses() { return Score.LOSSES; } } /* End of Spring Boot web service example class */
Step 5: Generate RESTful JSON responses
This step-by-step Spring Boot RESTful web services example needs to generate a JSON-based response for the client. There are excellent frameworks like Jackson and GSON, which you should use in larger projects, but for this simple RESTful web services example, we will simply employ some Java String manipulation to generate the JSON.
The getScore() method needs to return a JSON string formatted in the following manner:
{ "wins":"5", "losses":"3", "ties": "0"}
Here is how the un-annotated getScore() method looks when coded to return a JSON string:
public String getScore() { String pattern = "{ \"wins\":\"%s\", \"losses\":\"%s\", \"ties\": \"%s\"}"; return String.format(pattern,Score.WINS, Score.LOSSES, Score.TIES); }
Note that you’ll use this same pattern match and String format approach again to return a JSON-based representation of the score in the updateScore method.
Since the getScore() method now returns JSON, you need to add a new produces attribute to the @RequestMapping annotation. The fully annotated getScore() method that indicates that JSON will be returned to the calling program looks as follows:
@RequestMapping(value="/score", method=RequestMethod.GET, produces=MediaType.APPLICATION_JSON_VALUE) public String getScore() { String pattern = "{ \"wins\":\"%s\", \"losses\":\"%s\", \"ties\": \"%s\"}"; return String.format(pattern, Score.WINS, Score.LOSSES, Score.TIES); }
In order to generate JSON, the updateScore method follows a similar pattern of updated annotations and String manipulation within the code:
@RequestMapping(value="/score", method=RequestMethod.PUT, produces=MediaType.APPLICATION_JSON_VALUE) public String updateScore(int wins, int losses, int ties) { Score.WINS = wins; Score.TIES = ties; Score.LOSSES = losses; String pattern = "{ \"wins\":\"%s\", \"losses\":\"%s\", \"ties\": \"%s\"}"; return String.format(pattern,Score.WINS, Score.LOSSES, Score.TIES); }
QueryParam to method signature mapping
To update the ScoreService, the client will use the /score path while it passes query parameters to represent the number of wins, losses and ties. For example, a request to update the number of wins to 99, ties to 88 and losses to 7 would look like this:
http://www.mcnz.com/score?wins=99&ties=88&losses=7
As long as the updateScore method has method parameters that match the names of the query parameters, the Spring Boot web services framework will assign the queryParam values to the correspondingly named method signature parameter.
http://www.mcnz.com/score?wins=99&ties=88&losses=7 public String updateScore(int wins, int losses, int ties) { … }
The updateScore method will take the values passed into the method and assign them to the corresponding properties of the ScoreService class. An updated JSON string will be sent to the client indicating the new, updated value of the score. You’ll use the same process used to generate JSON in the getScore()method here. The full method implementation is as follows:
@RequestMapping(value="/score", method=RequestMethod.PUT, produces=MediaType.APPLICATION_JSON_VALUE) public String updateScore(int wins, int losses, int ties) { Score.WINS = wins; Score.TIES = ties; Score.LOSSES = losses; String pattern = "{ \"wins\":\"%s\", \"losses\":\"%s\", \"ties\": \"%s\"}"; return String.format(pattern, Score.WINS, Score.LOSSES, Score.TIES); }
With the updateScore method coded, the step-by-step Spring Boot RESTful web services example is code complete, and the only steps left are to test and deploy.
Step 6: Run the Spring Boot RESTful web service
To run the application, simply right click on the restful-spring-example project and choose Run As → Spring Boot App and Maven will package the application and deploy it to the STS server. When the console window indicates the Tomcat-based server has finished starting, open a browser window and go to localhost:8080/score/wins. A value of zero will appear.
Step 7: Test the RESTful Spring Boot service
To test the increaseWins method, run the following two CURL command in a Bash shell:
$ curl -X POST "http://localhost:8080/score/wins" $ curl -X GET "http://localhost:8080/score/"
The output of the second command is:
{ "wins":"1", "losses":"0", "ties": "0"}
Now trigger a PUT invocation, with query parameters being used to carry the payload:
$ curl -X PUT "http://localhost:8080/score?wins=31&losses=11&ties=22"
This results in an output of:
{ "wins":"31", "losses":"11", "ties": "22"}
And that’s it, a complete, step-by-step Spring Boot RESTful web services example that creates a fully functional Spring Boot application.
How to improve the RESTful Spring example
Now there is plenty of room for improvement and expansion when it comes to this step-by-step Spring Boot RESTful web services example.
Obviously, using the static variables in the Score class is a poor way to manage state, so at the very least we should offload the job of state management to a JavaBean with an ObjectOutputStream. And neither a JavaBeans or RESTful web service should be responsible for data persistence, so there will be opportunities to integrate Hibernate, JPA and Spring Boot web services. We could also invoke the Spring Boot RESTful web service example through a Spring MVC app or a Spring RestTemplate instead of CURL, and of course, it would be nice to package this app in an executable JAR file with an embedded Tomcat or embedded WebSphere Liberty server and deploy it as a microservice. But all of those things would complicate the example and distract from the core purpose, which is to demonstrate just how easy it is to develop a RESTful Spring web service using the Spring Boot framework.
These aforementioned issues will be addressed in subsequent tutorials. The source code for this step-by-step Spring Boot RESTful web services example can be found on GitHub.

Spring Boot and Embedded Servers – Tomcat, Jetty and Undertow
http://www.springboottutorial.com/spring-boot-with-embedded-servers-tomcat-jetty
You will learn
- What is an embedded server?
- Why are embedded servers getting popular?
- What are the different embedded servers that Spring Boot supports?
- How do you switch from one embedded server to another?
What is an Embedded Server?
Think about what you would need to be able to deploy your application (typically) on a virtual machine.
- Step 1 : Install Java
- Step 2 : Install the Web/Application Server (Tomcat/Websphere/Weblogic etc)
- Step 3 : Deploy the application war
What if we want to simplify this?
How about making the server a part of the application?
You would just need a virtual machine with Java installed and you would be able to directly deploy the application on the virtual machine. Isn’t it cool?
This idea is the genesis for Embedded Servers.
When we create an application deployable, we would embed the server (for example, tomcat) inside the deployable.
For example, for a Spring Boot Application, you can generate an application jar which contains Embedded Tomcat. You can run a web application as a normal Java application!
Embedded server implies that our deployable unit contains the binaries for the server (example, tomcat.jar).
Creating an Embedded Server Project with Spring Initializr
Spring Initializr http://start.spring.io/ is great tool to bootstrap your Spring Boot projects.
As shown in the image above, following steps have to be done
- Launch Spring Initializr and choose the following
- Choose
com.in28minutes.springboot.tutorial.basics.example
as Group - Choose
spring-boot-tutorial-basics
as Artifact - Choose following dependencies
- Web
- DevTools
- Choose
- Click Generate Project.
- Import the project into Eclipse. File -> Import -> Existing Maven Project.
Default Embedded Server with Spring Boot – Tomcat
We have included Spring Boot Starter Web in our dependencies when creating the spring boot project.
Let’s take a quick look at the dependencies for spring-boot-starter-web
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
<version>2.0.0.RELEASE</version>
<scope>compile</scope>
</dependency>
You can see that by default Starter Web includes a dependency on starter tomcat.
Starter Tomcat has the following dependencies.
<dependency>
<groupId>org.apache.tomcat.embed</groupId>
<artifactId>tomcat-embed-core</artifactId>
<version>8.5.23</version>
<scope>compile</scope>
</dependency>
<dependency>
<groupId>org.apache.tomcat.embed</groupId>
<artifactId>tomcat-embed-el</artifactId>
<version>8.5.23</version>
<scope>compile</scope>
</dependency>
<dependency>
<groupId>org.apache.tomcat.embed</groupId>
<artifactId>tomcat-embed-websocket</artifactId>
<version>8.5.23</version>
<scope>compile</scope>
</dependency>
Starter Tomcat brings in all the dependencies need to run Tomcat as an embedded server.
Run the web application using an Embedded Server
When you run SpringBootTutorialBasicsApplication.java as a Java Application, you would see that the server would start up and start serving requests.
An extract from the log
o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http)
You can see that tomcat has started by default on port 8080.
You can customize the port in application.properties
server.port=9080
When you do a ‘mvn clean install’ on the project, a jar artifact named spring-boot-tutorial-basics-0.0.1-SNAPSHOT.jar
is generated.
This jar can be used to run the application on any machine where Java 8 is installed.
The tomcat embedded server is also packaged inside this jar
Using Jetty as Embedded Server with Spring Boot
Remove the existing dependency on spring-boot-starter-web and add these in.
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<exclusions>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-jetty</artifactId>
</dependency>
Using Undertow as Embedded Server with Spring Boot
Remove the existing dependency on spring-boot-starter-web and add these in.
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<exclusions>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-undertow</artifactId>
</dependency>
Embedded Server Spring Boot Configuration
Spring Boot provides a number of options to configure the embedded server through application.properties
# EMBEDDED SERVER CONFIGURATION (ServerProperties)
server.compression.enabled=false # If response compression is enabled.
server.context-path= # Context path of the application.
server.display-name=application # Display name of the application.
server.error.include-stacktrace=never # When to include a "stacktrace" attribute.
server.error.path=/error # Path of the error controller.
server.error.whitelabel.enabled=true # Enable the default error page displayed in browsers in case of a server error.
server.port=8080 # Server HTTP port.
server.server-header= # Value to use for the Server response header (no header is sent if empty)
server.servlet-path=/ # Path of the main dispatcher servlet.
Here are a few Jetty specific options
server.jetty.acceptors= # Number of acceptor threads to use.
server.jetty.max-http-post-size=0 # Maximum size in bytes of the HTTP post or put content.
server.jetty.selectors= # Number of selector threads to use.
You can also configure ssl on the embedded server
server.ssl.ciphers= # Supported SSL ciphers.
server.ssl.client-auth= # Whether client authentication is wanted ("want") or needed ("need"). Requires a trust store.
server.ssl.enabled= # Enable SSL support.
server.ssl.enabled-protocols= # Enabled SSL protocols.
server.ssl.key-alias= # Alias that identifies the key in the key store.
server.ssl.key-password= # Password used to access the key in the key store.
server.ssl.key-store= # Path to the key store that holds the SSL certificate (typically a jks file).
server.ssl.key-store-password= # Password used to access the key store.
server.ssl.key-store-provider= # Provider for the key store.
server.ssl.key-store-type= # Type of the key store.
server.ssl.protocol=TLS # SSL protocol to use.
server.ssl.trust-store= # Trust store that holds SSL certificates.
server.ssl.trust-store-password= # Password used to access the trust store.
server.ssl.trust-store-provider= # Provider for the trust store.
server.ssl.trust-store-type= # Type of the trust store.
A few tomcat specific properties are listed below
server.tomcat.accept-count= # Maximum queue length for incoming connection requests when all possible request processing threads are in use.
server.tomcat.accesslog.directory=logs # Directory in which log files are created. Can be relative to the tomcat base dir or absolute.
server.tomcat.accesslog.enabled=false # Enable access log.
server.tomcat.basedir= # Tomcat base directory. If not specified a temporary directory will be used.
server.tomcat.max-connections= # Maximum number of connections that the server will accept and process at any given time.
server.tomcat.max-threads=0 # Maximum amount of worker threads.
server.tomcat.uri-encoding=UTF-8 # Character encoding to use to decode the URI.
For complete list options refer spring documentation – https://docs.spring.io/spring-boot/docs/current/reference/html/common-application-properties.html

Tutorial: Use Spring Boot to Build and Deploy WAR Files
https://stormpath.com/blog/tutorial-spring-boot-war-files
Spring Boot makes it easy to create stand-alone Java web applications. However in production environments, a web container often already exists. How do we deploy our apps in these situations and have them run side-by-side with other servlets? In this tutorial, we’ll walk through how to use WAR files to do just that.
Getting Started with With Spring Boot, Tomcat, and WAR Files
In a previous tutorial, we built a simple RESTful web app using Spring Boot. I’m going to use this as a base and show how to deploy it into a container. You can grab the code for this tutorial on GitHub.
To ensure an existing Spring Boot app is container-ready one needs do three things
– Renaming the embedded Tomcat libraries
– Repackage the output file as a WAR
– Wire the application up as a servlet
Tomcat Libraries
Building a Spring Boot application produces a runnable jar file by default. If your app includes server functionality, then Tomcat will be bundled with it. We need to ensure the Tomcat libraries don’t clash with an existing container (since the container will include the same libraries).
When we do a clean clone of our repo (grab the code on GitHub if you haven’t yet) and do an mvn clean package
we end up with a target directory containing our runnable jar.
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$ mvn clean package
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This jar contains Tomcat libraries. To confirm this, we can rename it to .zip
and look at the lib
directory.
You’ll see various .jar files starting with tomcat-
. Some of these will clash with a running instance of Tomcat. We need to tell Spring Boot to move them.
To WAR! AKA: Build Your WAR Files
First, we must tell Spring Boot we want a WAR file as output. This is as easy as adding one line to our pom.xml.
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<packaging>war</packaging>
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Now when we build the package with
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$ mvn clean package
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we will see a .war
file inside our target directory:
As before we can rename the file to .zip
to see what’s inside. Everything is basically the same, just slightly re-ordered. Now lib
is inside of WEB-INF and
demo` (where our project code sits) is in WEB-INF/classes.
Renaming Tomcat
Next, we tell Spring Boot to move our Tomcat libraries out of this folder. In our previous pom.xml we included three dependencies for our project – one for REST, one for data access, and another for the database.
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<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring–boot–starter–data–rest</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring–boot–starter–data–jpa</artifactId>
</dependency>
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
</dependency>
</dependencies>
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Now we append the Spring Boot Tomcat Starter to this (which links to the Tomcat libraries you need when embedding) and set the scope of the dependency to provided.
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<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring–boot–starter–data–rest</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring–boot–starter–data–jpa</artifactId>
</dependency>
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring–boot–starter–tomcat</artifactId>
<scope>provided</scope>
</dependency>
</dependencies>
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This will still include the .jar files as before but will put them in a new folder called lib-provided.
We can see this if we follow the same procedure as before. Once we mvn clean package and rename our .war to .zip we’ll see inside WEB-INF the new folder has appeared. Inside are all the embedded Tomcat libraries (and you’ll see they are no longer in lib).
Now our application will happily reside in a servlet container without clashing with its libraries.
Setting Up a Servlet
The only other thing we need to do is wire our application up to start as a servlet. And to do this we need to modify our application definition.
In the REST app mentioned our Application.java used the SpringBootApplication annotation on the main class and defined a main method.
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package demo;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
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To set the app up as a servlet we extend the main class with SpringBootServletInitializer and override the configure method using SpringApplicationBuilder.
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package demo;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.web.SpringBootServletInitializer;
import org.springframework.boot.builder.SpringApplicationBuilder;
@SpringBootApplication
public class Application extends SpringBootServletInitializer {
@Override
protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
return application.sources(Application.class);
}
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
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And that’s it! This application will now happily run inside a Tomcat container!
Installing Tomcat
Deploying WAR files to Tomcat is as easy as copying the file to Tomcat’s webapps directory. But first, you need to install Tomcat. On Ubuntu, you can use apt-get
.
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$ sudo apt–get install tomcat7
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This will install and start the server automatically on port 8080.
On Windows it’s just as easy – download and extract the binary distribution .zip file and run startup.bat
in the bin directory. This will open up a console window showing the output of Catalina.
In both cases, you can check to see if everything is running by browsing to localhost:8080
. You should see the Tomcat default homepage.
(Who knew Tomcat was so easy to use?!)
Copy the WAR File
The last step is copying the WAR to webapps
. Here the name is important – whatever filename we choose will be used to map HTTP requests to our application. (All done automatically! I think this is amazing.) In an attempt to be more URL-friendly, I’m going to use demo.war
.
On Ubuntu, this can be done with:
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$ sudo cp target/demo–0.0.1–SNAPSHOT.war /var/lib/tomcat7/webapps/demo.war
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In Windows, use Explorer for the copy and then wait for the console window to show deployment messages.
And that’s it! Just by copying one file across our app is automatically booted and running side-by-side with the default Tomcat servlet.
Test Your WAR File Deployment
As before we test this by making calls using curl. Normally we called get
on localhost
but now our application is mapped to /demo/
.
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$ curl localhost:8080/demo/
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This shows you available URLs. To see what people objects are available you can use:
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$ curl localhost:8080/demo/people
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Or, create new ones with:
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$ curl –X POST –H “Content-Type:application/json” –d ‘{ “firstName” : “Karl”, “lastName” : “Penzhorn” }’ localhost:8080/demo/persons
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Note: In my testing I found the deploy on Windows to be somewhat brittle. Sometimes I needed to close and rerun startup.bat
.
Run as a Standalone Application
One last thing – because our Tomcat libraries are still there (just moved) we are able to run this application on it’s own. So mvn spring-boot:run
still works !
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$ mvn spring–boot:run
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DEPLOY A SPRING BOOT APP ON YOUR OWN SERVER…
https://www.theguild.nl/deploy-a-spring-boot-app-on-your-own-server-in-less-than-15-minutes/
Hosted PaaS (Platform As A Service) offerings like Heroku and OpenShift are great but not always suitable or even possible to use. If you need or want full control over your data and servers, or you just want to host your latest side project but don’t want Heroku dyno sleeping you might just want to self host.
Traditionally self-hosting was painful and cumbersome but today there are plenty options to self-host your apps that are nearly as painless as a hosted PaaS solution. In this tutorial I will show you how to deploy an app on Dokku:
Dokku is an extensible, open source Platform as a Service that runs on a single server of your choice.
Dokku provides an environment very similar to Heroku technically, allowing Dokku to take advantage of Heroku buildpacks to deploy your apps. Dokku uses these buildpacks to automatically build Docker containers that can run your apps and services. Refer to the Dokku documentation for more information on Dokku.
For this tutorial we’ll be using this Spring Boot example app I’ve set up. It’s a very basic app with a single HTTP endpoint that serves up a semi-random quote retrieved from a Postgres database. It’s a completely vanilla Spring Boot app, except for a single file to instruct Dokku how to start the app but more on that later. Let’s get started!
1. GET A (VIRTUAL) SERVER
Get a server with root access. Dokku requires at least 1GB of RAM and officially only supports Ubuntu 14.04 x64.
For convenience you’ll want to assign a DNS hostname (dokku.example.org
) to your servers IP and preferably even assign a wildcard record so you can deploy apps on <app name>.dokku.example.org
.
2. INSTALL DOKKU
SSH into your server and execute the following command to kick off the Dokku installation. Run this either as root or make sure your user account has sudo permissions.
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wget -qO- https://raw.githubusercontent.com/dokku/dokku/v0.4.14/bootstrap.sh | bash
|
Sit back, get some coffee, this will take a couple of minutes. When the command completes open your browser and navigate to the ip address or hostname assigned to your server to complete the Dokku setup.
Provide your SSH public key here so you’ll be able to push your app to Dokku later via Git. Enable use virtualhost naming for apps
and enter the hostname you assigned to your server in step 1.
That’s it, you now have a fully functional Dokku instance up and running! Let’s see what it takes to actually deploy an app.
3. PREPARE YOUR APP FOR DEPLOYMENT ON DOKKU
We’re about ready to deploy our first app. In general if you want to deploy an app on Dokku you don’t need to make a lot of modifications to your app. Especially if your app adheres to the Twelve Factor guidelines you should be fine. Most importantly your app should allow configuration via environment variables or command line parameters.
Fortunately Spring Boot embraces the Twelve Factor guidelines. Spring Boot supports configuration via environment variables out of the box and it’s trivial to implement your own.
Looking at the example app I prepared there are two important things to notice:
1. I’ve created two property aliases to allow configuration via $PORT
and $DATABASE_URL
. This is not strictly necessary but I prefer the more generic environment variables over the Spring specific ones.
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// application.properties spring.datasource.url=${database.url:jdbc:postgresql://localhost:5432/dokku-demo} server.port=${port:8080} |
2. I’ve added a Procfile to instruct Dokku how to start our app. Dokku will read this file during deployment and use the web
process to boot our app. You can read more about Procfiles here.
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# Procfile web: env DATABASE_URL=$JDBC_DATABASE_URL target/dokku-boot-demo-0.0.1-SNAPSHOT.jar |
During deployment Dokku invokes mvn install
on our app so it will build a jar. Here we instruct Dokku that to launch our app it needs to execute the jar. We set the $DATABASE_URL
to $JDBC_DATABASE_URL
which is an environment variable provided by the Java buildpack that formats the database connection string for JDBC compatibility.
4. DEPLOY YOUR APP
Alright so now our app is Dokku compatible. Before we can push our app to Dokku we need to configure our application in Dokku. For simplicity enter the following dokku
commands in an SSH session on your server. Later you can setup the Dokku CLI client to run these commands directly from your local machine.
First we’ll create our app in Dokku:
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$ dokku apps:create my-app
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Next we’ll install the Dokku Postgres plugin:
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$ dokku plugin:install https://github.com/dokku/dokku-postgres.git postgres
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This will pull in a Postgres Docker image so give it some time to complete.
Next create a Postgres instance for our app:
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$ dokku postgres:create my-app-postgres
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Link it to our app:
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$ dokku postgres:link my-app-postgres my-app
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That’s all the configuration we need, let’s actually deploy our app now!
First clone the example app to your local machine:
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$ git clone https://github.com/kabisa/dokku-boot-demo.git $ cd dokku-boot-demo |
Dokku uses a Git push to deploy
model, meaning that you push your app sources into Dokku using Git. To deploy you simply add a git remote
to your repository pointing to Dokku and git push
every time you want to deploy your latest changes.
Execute the following command in your shell. Replace dokku.example.org
with your actual Dokku hostname.
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$ git remote add dokku dokku@dokku.example.org:my-app
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And finally push our app to Dokku:
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$ git push dokku master
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Dokku will now detect our app is a Java app, build a Docker image suitable to run Java apps, compile the app and run it.
You should see similar output as below:
Open your browser at http://my-app.dokku.example.org/
and see a nice random quote!
CLOSING THOUGHTS
Dokku takes a bit of one time setup but once you have your Dokku instance ready, deploying new applications will be a breeze. Do note that Dokku was designed for simple single server setups. If you need fancy stuff like clustering, access control etc you might want to look at one of the more comprehensive projects in this space like Flynn, Deis or Cloud Foundry.
Even though Dokku is quite simple, we’ve only scratched the surface of what it can do. You now have a fully functional Dokku instance so go ahead and explore the Dokku docs to see what more is possible!
If there’s no suitable Heroku buildpack for your app you can always deploy a raw Docker container using Dokku by simply including a Dockerfile
in the root of your project.
If you’re planning to deploy a more complex Spring Boot app to Dokku you might want to look into Spring Cloud Connectors. Spring Cloud Connectors can automatically detect that you’re running in a cloud platform, and configure your HTTP port and database automatically for you. Spring Cloud Connectors officially don’t support Dokku, but the Heroku support works just fine with Dokku.
Also be sure to check out the plugins that Dokku offers to make use of databases, message brokers etc. There’s even a Dokku Let’s Encrypt plugin for dead easy Let’s Encrypt SSL certificates.
Happy deploying!
