使用Java写一个WebSocket的例子

好的，以下是一个使用 Java API 实现 WebSocket 的例子：

1. 创建一个类并实现 javax.websocket.Endpoint 接口

import java.io.IOException;
import java.nio.ByteBuffer;
import javax.websocket.Endpoint;
import javax.websocket.EndpointConfig;
import javax.websocket.MessageHandler;
import javax.websocket.Session;

public class MyEndpoint extends Endpoint {

    @Override
    public void onOpen(Session session, EndpointConfig config) {
        System.out.println("WebSocket opened: " + session.getId());

        // Add a message handler to the session
        session.addMessageHandler(new MessageHandler.Whole<String>() {
            @Override
            public void onMessage(String message) {
                System.out.println("Message received: " + message);

                // Send a message back to the client
                try {
                    session.getBasicRemote().sendText("Received message: " + message);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        });

        // Add a binary message handler to the session
        session.addMessageHandler(new MessageHandler.Whole<ByteBuffer>() {
            @Override
            public void onMessage(ByteBuffer message) {
                System.out.println("Binary message received: " + message);

                // Send a binary message back to the client
                try {
                    session.getBasicRemote().sendBinary(message);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        });
    }

    @Override
    public void onClose(Session session, CloseReason closeReason) {
        System.out.println("WebSocket closed: " + session.getId() + " Reason: " + closeReason);
    }

    @Override
    public void onError(Session session, Throwable throwable) {
        System.out.println("WebSocket error: " + session.getId());
        throwable.printStackTrace();
    }
}

2. 使用 javax.websocket.server.ServerEndpoint 注解指定 WebSocket 的路径

import javax.websocket.server.ServerEndpoint;

@ServerEndpoint("/my-websocket")
public class MyWebSocketServer {

    public MyWebSocketServer() {
        System.out.println("WebSocket server started.");
    }
}

3. 启动 WebSocket 服务器

import javax.websocket.server.ServerContainer;
import javax.websocket.server.ServerEndpointConfig;
import org.apache.tomcat.websocket.server.Constants;
import org.apache.tomcat.websocket.server.WsSci;

public class WebSocketServerApp {

    public static void main(String[] args) throws Exception {
        // Start embedded Tomcat
        Tomcat tomcat = new Tomcat();
        tomcat.setPort(8080);

        // Add WebSocket support
        tomcat.addWebapp("/my-webapp", new File(".").getAbsolutePath());
        tomcat.getServletContext().setExtendedListenerTypes(true);
        tomcat.getServletContext().addListener(new WsSci());

        // Add WebSocket endpoint
        ServerContainer serverContainer =
                (ServerContainer) tomcat.getServletContext().getAttribute(Constants.SERVER_CONTAINER_SERVLET_CONTEXT_ATTRIBUTE);
        ServerEndpointConfig serverEndpointConfig = ServerEndpointConfig.Builder.create(MyEndpoint.class, "/my-websocket").build();
        serverContainer.addEndpoint(serverEndpointConfig);

        // Start Tomcat
        tomcat.start();
        tomcat.getServer().await();
    }
}

以上代码启动一个 WebSocket 服务器，监听在 `ws://localhost:8080/my-webapp/my-websocket` 路径，可以接收文本和二进制消息，并原样返回给客户端。