#014: Working with Spring Boot and WebSockets
WebSockets are a powerful tool for building real-time applications. Spring Boot makes it easy to work with WebSockets. In this post, we'll learn how to work with Spring Boot and WebSockets.
##What are WebSockets?
WebSockets are a communication protocol that allows for full-duplex communication between a client and a server. This means that both the client and the server can send and receive data at the same time.
WebSockets are a great way to build real-time applications. They are fast, efficient, and they allow you to push data to the client as soon as it is available.
##Setting up Spring Boot
Let's start by setting up a simple Spring Boot application. We'll use the Spring Initializr to create our project.
Go to the Spring Initializr website (https://start.spring.io/).
Choose the following options:
Click Generate Project.
You should now have a zip file that contains everything you need to get started. Unzip the file and open it in your favorite IDE.
##Creating a WebSocket Endpoint
Let's start by creating a simple WebSocket endpoint. We'll use the @ServerEndpoint annotation to create our endpoint.
Create a new Java class in the com.example.websockets.demo package and name it MyWebSocketEndpoint.java.
Add the following code to the MyWebSocketEndpoint.java file:
@ServerEndpoint("/websocket")
public class MyWebSocketEndpoint {
}
The @ServerEndpoint annotation is used to create a WebSocket endpoint. The value of the annotation is the path that will be used to access the endpoint.
##Sending and Receiving Messages
Now that we have our endpoint, let's add some code to send and receive messages.
Add the following code to the MyWebSocketEndpoint.java file:
@ServerEndpoint("/websocket")
public class MyWebSocketEndpoint {
@OnOpen
public void onOpen(Session session) {
// do something when the connection is opened
}
@OnMessage
public void onMessage(String message, Session session) {
// do something when a message is received
}
@OnClose
public void onClose(Session session) {
// do something when the connection is closed
}
@OnError
public void onError(Throwable error) {
// do something when there is an error
}
}
The @OnOpen annotation is used to specify a method that will be called when a connection is opened. The @OnMessage annotation is used to specify a method that will be called when a message is received. The @OnClose annotation is used to specify a method that will be called when a connection is closed. The @OnError annotation is used to specify a method that will be called when there is an error.
##Configuring the Endpoint
Now that we have our endpoint, let's configure it.
Add the following code to the MyWebSocketEndpoint.java file:
@ServerEndpoint("/websocket")
public class MyWebSocketEndpoint {
@OnOpen
public void onOpen(Session session) {
// do something when the connection is opened
}
@OnMessage
public void onMessage(String message, Session session) {
// do something when a message is received
}
@OnClose
public void onClose(Session session) {
// do something when the connection is closed
}
@OnError
public void onError(Throwable error) {
// do something when there is an error
}
}
The @ServerEndpoint annotation is used to create a WebSocket endpoint. The value of the annotation is the path that will be used to access the endpoint.
The @OnOpen annotation is used to specify a method that will be called when a connection is opened. The @OnMessage annotation is used to specify a method that will be called when a message is received. The @OnClose annotation is used to specify a method that will be called when a connection is closed. The @OnError annotation is used to specify a method that will be called when there is an error.
##Testing the Endpoint
Now that we have our endpoint, let's test it.
Create a new Java class in the com.example.websockets.demo package and name it MyWebSocketEndpointTest.java.
Add the following code to the MyWebSocketEndpointTest.java file:
@Test
public void testMyWebSocketEndpoint() throws Exception {
URI uri = new URI("ws://localhost:8080/websocket");
WebSocketContainer container = ContainerProvider.getWebSocketContainer();
Session session = container.connectToServer(MyWebSocketEndpoint.class, uri);
session.getBasicRemote().sendText("Hello world!");
session.close();
}
In the testMyWebSocketEndpoint() method, we create a URI for our WebSocket endpoint. We then create a WebSocketContainer and connect to our endpoint. We send a message to the server and then close the connection.
If you run the test, you should see the following output:
Hello world!
##Conclusion
In this post, we've learned how to work with Spring Boot and WebSockets. We've created a simple WebSocket endpoint and tested it.