README.md 20 KB
This guide walks you through the process of creating a "hello world" STOMP messaging server with Spring.
What you'll build
You'll build a server that will accept a message carrying a user's name. In response, it will push a greeting into a queue that the client is subscribed to.
What you'll need
- About 15 minutes
- A favorite text editor or IDE
- JDK 6 or later
- Gradle 1.8+ or Maven 3.0+
- You can also import the code from this guide as well as view the web page directly into Spring Tool Suite (STS) and work your way through it from there.
How to complete this guide
Like all Spring's Getting Started guides, you can start from scratch and complete each step, or you can bypass basic setup steps that are already familiar to you. Either way, you end up with working code.
To start from scratch, move on to Set up the project.
To skip the basics, do the following:
- Download and unzip the source repository for this guide, or clone it using Git:
git clone https://github.com/spring-guides/gs-messaging-stomp-websocket.git - cd into
gs-messaging-stomp-websocket/initial. - Jump ahead to Create a resource representation class.
When you're finished, you can check your results against the code in gs-messaging-stomp-websocket/complete.
Set up the project
First you set up a basic build script. You can use any build system you like when building apps with Spring, but the code you need to work with Gradle and Maven is included here. If you're not familiar with either, refer to Building Java Projects with Gradle or Building Java Projects with Maven.
Create the directory structure
In a project directory of your choosing, create the following subdirectory structure; for example, with mkdir -p src/main/java/hello on *nix systems:
└── src
└── main
└── java
└── hello
Create a Gradle build file
Below is the initial Gradle build file. But you can also use Maven. The pom.xml file is included right here. If you are using Spring Tool Suite (STS), you can import the guide directly.
build.gradle
apply plugin: 'java'
apply plugin: 'war'
apply plugin: 'eclipse'
apply plugin: 'idea'
war {
baseName = 'gs-messaging-websocket'
version = '0.1.0'
}
repositories {
mavenCentral()
maven { url "http://repo.springsource.org/libs-snapshot" }
}
dependencies {
compile("org.springframework:spring-webmvc:4.0.0.BUILD-SNAPSHOT")
compile("org.springframework:spring-websocket:4.0.0.BUILD-SNAPSHOT")
providedCompile("javax.websocket:javax.websocket-api:1.0-rc5")
providedCompile("javax.servlet:javax.servlet-api:3.1-b09")
testCompile("junit:junit:4.11")
}
task wrapper(type: Wrapper) {
gradleVersion = '1.6'
}
Note: This guide is using Spring Boot.
Create a resource representation class
Now that you've set up the project and build system, you can create your STOMP message service.
Begin the process by thinking about service interactions.
The service will accept messages containing a name in a STOMP message whose body is a JSON object. If the name given is "Fred", then the message might look something like this:
{
"name": "Fred"
}
To model the message carrying the name, you can create a plain old Java object with a name property and a corresponding getName() method:
src/main/java/hello/HelloMessage.java
package hello;
public class HelloMessage {
private String name;
public String getName() {
return name;
}
}
Upon receiving the message and extracting the name, the service will process it by creating a greeting and publishing that greeting on a separate queue that the client is subscribed to. The greeting will also be a JSON object, which might look something like this:
{
"content": "Hello, Fred!"
}
To model the greeting representation, you add another plain old Java object with a content property and corresponding getContent() method:
src/main/java/hello/Greeting.java
package hello;
public class Greeting {
private String content;
public Greeting(String content) {
this.content = content;
}
public String getContent() {
return content;
}
}
Spring will use the Jackson JSON library to automatically marshal instances of type Greeting into JSON.
Next, you'll create a controller to receive the hello message and send a greeting message.
Create a message-handling controller
In Spring's approach to working with STOMP messaging, STOMP messages can be handled by a controller. These components are easily identified by the @Controller annotation, and the GreetingController below is mapped to handle messages published on the "/app/hello" destination.
src/main/java/hello/GreetingController.java
package hello;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.messaging.handler.annotation.MessageMapping;
import org.springframework.messaging.simp.SimpMessageSendingOperations;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestBody;
@Controller
public class GreetingController {
private SimpMessageSendingOperations messagingTemplate;
@Autowired
public GreetingController(SimpMessageSendingOperations messagingTemplate) {
this.messagingTemplate = messagingTemplate;
}
@MessageMapping("/app/hello")
public void greeting(@RequestBody HelloMessage message) throws Exception {
Thread.sleep(3000); // simulated delay
Greeting greeting = new Greeting("Hello, " + message.getName() + "!");
messagingTemplate.convertAndSend("/queue/greetings", greeting);
}
}
This controller is concise and simple, but there's plenty going on. Let's break it down step by step.
The @MessageMapping annotation ensures that if a message is published on the "/app/hello" destination, then the greeting() method is called.
@RequestBody binds the payload of the message to a HelloMessage object which is passed into greeting().
Internally, the implementation of the method simulates a processing delay by causing the thread to sleep for 3 seconds. This is to demonstrate that after the client sends a message, the server can take as long as it needs to process the message asynchronously. The client may continue with whatever work it needs to do without waiting on the response.
After the 3 second delay, the greeting() method creates a new Greeting object, setting its content to say "Hello" to the name from the HelloMessage. It then calls convertAndSend() on the injected SimpMessageSendingOperations to send the Greeting on the "/queue/greetings" destination.
The Greeting object must be converted to JSON. Thanks to Spring's HTTP message converter support, you don't need to do this conversion manually. When you configure Spring for STOMP messaging, you'll inject SimpMessagingTemplate with an instance of MappingJackson2MessageConverter. It will be used to convert the Greeting instance to JSON.
Configure Spring for STOMP messaging
Now that the essential components of the service are created, you can configure Spring to enable WebSocket and STOMP messaging.
Create a Java class named WebSocketConfig that looks like this:
src/main/java/hello/WebSocketConfig.java
package hello;
import org.springframework.context.annotation.Configuration;
import org.springframework.messaging.simp.config.EnableWebSocketMessageBroker;
import org.springframework.messaging.simp.config.MessageBrokerConfigurer;
import org.springframework.messaging.simp.config.StompEndpointRegistry;
import org.springframework.messaging.simp.config.WebSocketMessageBrokerConfigurer;
@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {
@Override
public void configureMessageBroker(MessageBrokerConfigurer config) {
config.enableSimpleBroker("/queue");
config.setAnnotationMethodDestinationPrefixes("/app");
}
@Override
public void registerStompEndpoints(StompEndpointRegistry registry) {
registry.addEndpoint("/hello").withSockJS();
}
}
WebSocketConfig is annotated with @Configuration to indicate that it is a Spring configuration class.
It is also annotated @EnableWebSocketMessageBroker.
As its name suggests, @EnableWebSocketMessageBroker enables a WebSocket message handling, backed by a message broker.
The configureMessageBroker() method overrides the default method in WebSocketMessageBrokerConfigurer to configure the message broker.
It starts by calling enableSimpleBroker() to enable a simple memory-based message broker to carry the greeting messages back to the client on destinations prefixed with "/queue".
It also designates the "/app" prefix for messages that are bound for @MessageMapping-annotated methods.
The registerStompEndpoints() method registers the "/hello" endpoint (which, along with the "/app" prefix, is handled by GreetingController's greeting() method).
In doing so, it enables SockJS fallback options on that endpoint so that alternative messaging options may be used if WebSocket is not available.
Create a browser client
With the server side pieces in place, now let's turn our attention to the JavaScript client that will send messages to and receive messages from the server side.
Create an index.html file that looks like this:
src/main/resources/static/index.html
<!DOCTYPE html>
<html>
<head>
<title>Hello WebSocket</title>
<script src="sockjs-0.3.4.js"></script>
<script src="stomp.js"></script>
<script type="text/javascript">
var stompClient = null;
function setConnected(connected) {
document.getElementById('connect').disabled = connected;
document.getElementById('disconnect').disabled = !connected;
document.getElementById('conversationDiv').style.visibility = connected ? 'visible' : 'hidden';
document.getElementById('response').innerHTML = '';
}
function connect() {
var socket = new SockJS('/hello');
stompClient = Stomp.over(socket);
stompClient.connect('', '', function(frame) {
setConnected(true);
console.log('Connected: ' + frame);
stompClient.subscribe('/queue/greetings', function(greeting){
showGreeting(JSON.parse(greeting.body).content);
});
});
}
function disconnect() {
stompClient.disconnect();
setConnected(false);
console.log("Disconnected");
}
function sendName() {
var name = document.getElementById('name').value;
stompClient.send("/app/hello", {}, JSON.stringify({ 'name': name }));
}
function showGreeting(message) {
var response = document.getElementById('response');
var p = document.createElement('p');
p.style.wordWrap = 'break-word';
p.appendChild(document.createTextNode(message));
response.appendChild(p);
}
</script>
</head>
<body>
<noscript><h2 style="color: #ff0000">Seems your browser doesn't support Javascript! Websocket relies on Javascript being enabled. Please enable
Javascript and reload this page!</h2></noscript>
<div>
<div>
<button id="connect" onclick="connect();">Connect</button>
<button id="disconnect" disabled="disabled" onclick="disconnect();">Disconnect</button>
</div>
<div id="conversationDiv">
<label>What is your name?</label><input type="text" id="name" />
<button id="sendName" onclick="sendName();">Send</button>
<p id="response"></p>
</div>
</div>
</body>
</html>
The main piece of this HTML file to pay attention to is the JavaScript code in the connect() and sendName() functions.
The connect() function uses SockJS and stomp.js to open a connection to "/gs-messaging-stomp-websocket/hello", which is where GreetingController is waiting for connections. Upon a successful connection, it subscribes to the "/queue/greetings" destination, where the server will publish greeting messages. When a greeting appears on that queue, it will append a paragraph element to the DOM to display the greeting message.
The sendName() function retrieves the name entered by the user and uses the STOMP client to send it to the "/app/hello" destination (where GreetingController.greeting() will receive it).
Make the application executable
Although it is possible to package this service as a traditional [WAR][u-war] file for deployment to an external application server, the simpler approach demonstrated below creates a standalone application. You package everything in a single, executable JAR file, driven by a good old Java main() method. Along the way, you use Spring's support for embedding the [Tomcat][u-tomcat] servlet container as the HTTP runtime, instead of deploying to an external instance.
Create an Application class
src/main/java/hello/Application.java
package hello;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.SpringApplication;
import org.springframework.context.annotation.ComponentScan;
@ComponentScan
@EnableAutoConfiguration
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
The main() method defers to the [SpringApplication][] helper class, providing Application.class as an argument to its run() method. This tells Spring to read the annotation metadata from Application and to manage it as a component in the [Spring application context][u-application-context].
The @ComponentScan annotation tells Spring to search recursively through the hello package and its children for classes marked directly or indirectly with Spring's [@Component][] annotation. This directive ensures that Spring finds and registers the GreetingController, because it is marked with @Controller, which in turn is a kind of @Component annotation.
The [@EnableAutoConfiguration][] annotation switches on reasonable default behaviors based on the content of your classpath. For example, because the application depends on the embeddable version of Tomcat (tomcat-embed-core.jar), a Tomcat server is set up and configured with reasonable defaults on your behalf. And because the application also depends on Spring MVC (spring-webmvc.jar), a Spring MVC [DispatcherServlet][] is configured and registered for you — no web.xml necessary! Auto-configuration is a powerful, flexible mechanism. See the [API documentation][@EnableAutoConfiguration] for further details.
Build an executable JAR
Now that your Application class is ready, you simply instruct the build system to create a single, executable jar containing everything. This makes it easy to ship, version, and deploy the service as an application throughout the development lifecycle, across different environments, and so forth.
Below are the Gradle steps, but if you are using Maven, you can find the updated pom.xml right here and build it by typing mvn clean package.
Update your Gradle build.gradle file's buildscript section, so that it looks like this:
buildscript {
repositories {
maven { url "http://repo.spring.io/libs-snapshot" }
mavenLocal()
}
dependencies {
classpath("org.springframework.boot:spring-boot-gradle-plugin:0.5.0.M6")
}
}
Further down inside build.gradle, add the following to the list of applied plugins:
apply plugin: 'spring-boot'
You can see the final version of build.gradle [right here]((https://github.com/spring-guides/gs-messaging-stomp-websocket/blob/master/complete/build.gradle).
The Spring Boot gradle plugin collects all the jars on the classpath and builds a single "über-jar", which makes it more convenient to execute and transport your service.
It also searches for the public static void main() method to flag as a runnable class.
Now run the following command to produce a single executable JAR file containing all necessary dependency classes and resources:
$ ./gradlew build
If you are using Gradle, you can run the JAR by typing:
$ java -jar build/libs/gs-messaging-stomp-websocket-0.1.0.jar
If you are using Maven, you can run the JAR by typing:
$ java -jar target/gs-messaging-stomp-websocket-0.1.0.jar
Note: The procedure above will create a runnable JAR. You can also opt to build a classic WAR file instead.
Run the service
If you are using Gradle, you can run your service at the command line this way:
$ ./gradlew clean build && java -jar build/libs/gs-messaging-stomp-websocket-0.1.0.jar
Note: If you are using Maven, you can run your service by typing
mvn clean package && java -jar target/gs-messaging-stomp-websocket-0.1.0.jar.
Logging output is displayed. The service should be up and running within a few seconds.
Test the service
Now that the service is running, point your browser at http://localhost:8080 and click the "Connect" button.
Upon opening a connection, you are asked for your name. Enter your name and click "Send". Your name is sent to the server as a JSON message over STOMP. After a 3-second simulated delay, the server sends a message back with a "Hello" greeting that is displayed on the page. At this point, you can send another name, or you can click the "Disconnect" button to close the connection.
Summary
Congratulations! You've just developed a STOMP-based messaging service with Spring.
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