Working with Websockets in Java

Introduction

Websockets provide a full-duplex communication channel over a single, long-lived connection between a client and a server. Java provides libraries for implementing both websocket clients and servers.

1. Websocket Server

Using Tyrus (Reference Implementation for JSR 356)

Tyrus is the reference implementation for JSR 356, the Java API for websocket. You can create a websocket server using Tyrus.

1. Add Tyrus dependency to your pom.xml:

   <dependency>
       <groupId>org.glassfish.tyrus</groupId>
       <artifactId>tyrus-server</artifactId>
       <version>1.17</version>
   </dependency>

2. Implement a websocket endpoint:

   import javax.websocket.*;
   import javax.websocket.server.*;
   
   @ServerEndpoint("/websocket")
   public class MyWebSocketServer {
   
       @OnOpen
       public void onOpen(Session session) {
           System.out.println("Client connected");
       }
   
       @OnMessage
       public String onMessage(String message) {
           System.out.println("Received message: " + message);
           return "Server received: " + message;
       }
   
       @OnClose
       public void onClose(Session session) {
           System.out.println("Connection closed");
       }
   }

Using Spring Framework

Spring Framework provides support for building websocket servers with the WebSocketHandler interface.

1. Add Spring Websocket dependency to your pom.xml:

   <dependency>
       <groupId>org.springframework.boot</groupId>
       <artifactId>spring-boot-starter-websocket</artifactId>
   </dependency>

2. Implement a WebSocketHandler:

   import org.springframework.web.socket.*;
   import org.springframework.web.socket.handler.TextWebSocketHandler;
   
   public class MyWebSocketHandler extends TextWebSocketHandler {
   
       @Override
       public void afterConnectionEstablished(WebSocketSession session) throws Exception {
           System.out.println("Connection established");
       }
   
       @Override
       protected void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {
           System.out.println("Received message: " + message.getPayload());
           session.sendMessage(new TextMessage("Server received: " + message.getPayload()));
       }
   }

2. Websocket Client

Using Tyrus

You can create a websocket client using Tyrus.

1. Add Tyrus dependency to your pom.xml (same as server):

2. Implement a websocket client:

   import javax.websocket.*;
   import java.net.URI;
   
   @ClientEndpoint
   public class MyWebSocketClient {
   
       @OnOpen
       public void onOpen(Session session) {
           System.out.println("Connected to server");
           session.getAsyncRemote().sendText("Hello, Server");
       }
   
       @OnMessage
       public void onMessage(String message) {
           System.out.println("Received message from server: " + message);
       }
   
       @OnClose
       public void onClose(Session session) {
           System.out.println("Connection closed");
       }
   
       public static void main(String[] args) {
           String uri = "ws://localhost:8080/websocket";
           WebSocketContainer container = ContainerProvider.getWebSocketContainer();
           try {
               container.connectToServer(MyWebSocketClient.class, URI.create(uri));
           } catch (Exception ex) {
               ex.printStackTrace();
           }
       }
   }

Using Spring Framework

1. Add Spring Websocket dependency to your pom.xml (same as server):

2. Implement a WebSocketHandler:

   import org.springframework.web.socket.*;
   import org.springframework.web.socket.handler.TextWebSocketHandler;
   
   public class MyWebSocketHandler extends TextWebSocketHandler {
   
       @Override
       public void afterConnectionEstablished(WebSocketSession session) throws Exception {
           System.out.println("Connected to server");
           session.sendMessage(new TextMessage("Hello, Server"));
       }
   
       @Override
       protected void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {
           System.out.println("Received message from server: " + message.getPayload());
       }
   
       @Override
       public void afterConnectionClosed(WebSocketSession session, CloseStatus status) throws Exception {
           System.out.println("Connection closed");
       }
   }

3. Best Practices

• Keep Messages Lightweight: Minimize the size of messages exchanged over the websocket connection to improve performance.
• Handle Errors Gracefully: Implement error handling mechanisms to deal with connection failures, timeouts, and other issues.
• Use Secure Websockets (WSS): For secure communication, use WSS (Websockets over HTTPS) instead of WS.

Conclusion

Websockets provide a powerful mechanism for real-time communication between clients and servers. In Java, you can implement websocket servers and clients using libraries like Tyrus and Spring Websocket. Understanding how to use these libraries effectively will enable you to build robust and scalable websocket-based applications.