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本文是基于Netty快速上手WebSocket客户端，不涉及WebSocket的TLS/SSL加密传输。

WebSocket原理参考【WebSocket简介-CSDN博客】，测试用的WebSocket服务端也是用Netty实现的，参考【基于Netty实现WebSocket服务端-CSDN博客】

一、基于Netty快速实现WebSocket客户端

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.http.DefaultHttpHeaders;
import io.netty.handler.codec.http.HttpClientCodec;
import io.netty.handler.codec.http.HttpObjectAggregator;
import io.netty.handler.codec.http.websocketx.TextWebSocketFrame;
import io.netty.handler.codec.http.websocketx.WebSocketClientHandshakerFactory;
import io.netty.handler.codec.http.websocketx.WebSocketClientProtocolHandler;
import io.netty.handler.codec.http.websocketx.WebSocketVersion;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import io.netty.handler.stream.ChunkedWriteHandler;
import lombok.extern.slf4j.Slf4j;import java.net.URI;
import java.util.concurrent.CountDownLatch;/*** https://blog.csdn.net/a1053765496/article/details/130701218* 基于Netty快速实现WebSocket客户端，不手动处理握手*/
@Slf4j
public class SimpleWsClient {final CountDownLatch latch = new CountDownLatch(1);public static void main(String[] args) throws Exception {SimpleWsClient client = new SimpleWsClient();client.test();}public void test() throws Exception {Channel dest = dest();latch.await();dest.writeAndFlush(new TextWebSocketFrame("CountDownLatch完成后发送的消息"));}public Channel dest() throws Exception {final URI webSocketURL = new URI("ws://127.0.0.1:7070/helloWs");EventLoopGroup group = new NioEventLoopGroup();Bootstrap boot = new Bootstrap();boot.option(ChannelOption.SO_KEEPALIVE, true).option(ChannelOption.TCP_NODELAY, true).group(group).handler(new LoggingHandler(LogLevel.INFO)).channel(NioSocketChannel.class).handler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel sc) throws Exception {ChannelPipeline pipeline = sc.pipeline();pipeline.addLast(new HttpClientCodec());pipeline.addLast(new ChunkedWriteHandler());pipeline.addLast(new HttpObjectAggregator(64 * 1024));pipeline.addLast(new WebSocketClientProtocolHandler(WebSocketClientHandshakerFactory.newHandshaker(webSocketURL, WebSocketVersion.V13, null, false, new DefaultHttpHeaders())));pipeline.addLast(new SimpleChannelInboundHandler<TextWebSocketFrame>() {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, TextWebSocketFrame msg)throws Exception {System.err.println(" 客户端收到消息======== " + msg.text());}@Overridepublic void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {if (WebSocketClientProtocolHandler.ClientHandshakeStateEvent.HANDSHAKE_COMPLETE.equals(evt)) {log.info(ctx.channel().id().asShortText() + " 握手完成！");latch.countDown();send(ctx.channel());}super.userEventTriggered(ctx, evt);}});}});ChannelFuture cf = boot.connect(webSocketURL.getHost(), webSocketURL.getPort()).sync();return cf.channel();}public static void send(Channel channel) {final String textMsg = "握手完成后直接发送的消息";if (channel != null && channel.isActive()) {TextWebSocketFrame frame = new TextWebSocketFrame(textMsg);channel.writeAndFlush(frame).addListener((ChannelFutureListener) channelFuture -> {if (channelFuture.isDone() && channelFuture.isSuccess()) {log.info("     ================= 发送成功.");} else {channelFuture.channel().close();log.info("     ================= 发送失败. cause = " + channelFuture.cause());channelFuture.cause().printStackTrace();}});} else {log.error("消息发送失败！ textMsg = " + textMsg);}}}

这里我们不手动进行握手，由Netty通过WebSocketClientProtocolHandler进行握手，但是我们要知道何时握手完成了。握手完成了我们才能进行正常的消息读写。

握手事件是在自定义的Handler中实现的，这里为了方便使用CountDownLatch，使用了匿名内部类SimpleChannelInboundHandler的方式。userEventTriggered这个方法会接收到所有的事件，其中就包括握手完成事件。

二、基于Netty，手动处理WebSocket握手信息：

客户端启动代码：

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.Unpooled;
import io.netty.channel.Channel;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.http.DefaultHttpHeaders;
import io.netty.handler.codec.http.HttpClientCodec;
import io.netty.handler.codec.http.HttpObjectAggregator;
import io.netty.handler.codec.http.websocketx.CloseWebSocketFrame;
import io.netty.handler.codec.http.websocketx.PingWebSocketFrame;
import io.netty.handler.codec.http.websocketx.TextWebSocketFrame;
import io.netty.handler.codec.http.websocketx.WebSocketClientHandshakerFactory;
import io.netty.handler.codec.http.websocketx.WebSocketFrame;
import io.netty.handler.codec.http.websocketx.WebSocketVersion;import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URI;/*** https://gitcode.com/ddean2009/learn-netty4/tree/master/src/main/java/com/flydean25/socketclient* https://www.flydean.com/25-netty-websocket-client* https://blog.csdn.net/superfjj/article/details/120648434* https://blog.csdn.net/twypx/article/details/84543518*/
public final class NettyWsClient {static final String URL = System.getProperty("url", "ws://127.0.0.1:7070/helloWs");public static void main(String[] args) throws Exception {URI uri = new URI(URL);final int port = uri.getPort();EventLoopGroup group = new NioEventLoopGroup();try {WebSocketClientHandler handler = new WebSocketClientHandler(WebSocketClientHandshakerFactory.newHandshaker(uri, WebSocketVersion.V13, null, true, new DefaultHttpHeaders()));Bootstrap b = new Bootstrap();b.group(group).channel(NioSocketChannel.class).handler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) {ChannelPipeline p = ch.pipeline();p.addLast(new HttpClientCodec(), new HttpObjectAggregator(8192), handler);}});Channel ch = b.connect(uri.getHost(), port).sync().channel();handler.handshakeFuture().sync();BufferedReader console = new BufferedReader(new InputStreamReader(System.in));while (true) {String msg = console.readLine();if (msg == null) {break;} else if ("再见".equalsIgnoreCase(msg)) {ch.writeAndFlush(new CloseWebSocketFrame());ch.closeFuture().sync();break;} else if ("ping".equalsIgnoreCase(msg)) {WebSocketFrame frame = new PingWebSocketFrame(Unpooled.wrappedBuffer(new byte[] {8, 1, 8, 1}));ch.writeAndFlush(frame);} else {WebSocketFrame frame = new TextWebSocketFrame(msg);ch.writeAndFlush(frame);}}} finally {group.shutdownGracefully();}}
}

客户端Handler

import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelPromise;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.codec.http.FullHttpResponse;
import io.netty.handler.codec.http.websocketx.CloseWebSocketFrame;
import io.netty.handler.codec.http.websocketx.PongWebSocketFrame;
import io.netty.handler.codec.http.websocketx.TextWebSocketFrame;
import io.netty.handler.codec.http.websocketx.WebSocketClientHandshaker;
import io.netty.handler.codec.http.websocketx.WebSocketFrame;
import io.netty.handler.codec.http.websocketx.WebSocketHandshakeException;
import io.netty.util.CharsetUtil;
import lombok.extern.slf4j.Slf4j;@Slf4j
public class WebSocketClientHandler extends SimpleChannelInboundHandler<Object> {private final WebSocketClientHandshaker handshaker;private ChannelPromise handshakeFuture;public WebSocketClientHandler(WebSocketClientHandshaker handshaker) {this.handshaker = handshaker;}public ChannelFuture handshakeFuture() {return handshakeFuture;}@Overridepublic void handlerAdded(ChannelHandlerContext ctx) {handshakeFuture = ctx.newPromise();}@Overridepublic void channelActive(ChannelHandlerContext ctx) {log.info("channelActive, 进行handshake");handshaker.handshake(ctx.channel());}@Overridepublic void channelInactive(ChannelHandlerContext ctx) {log.info("channelInactive!");}@Overridepublic void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {Channel ch = ctx.channel();if (!handshaker.isHandshakeComplete()) {try {handshaker.finishHandshake(ch, (FullHttpResponse) msg);log.info("websocket Handshake 完成!");handshakeFuture.setSuccess();} catch (WebSocketHandshakeException e) {log.info("websocket连接失败!");handshakeFuture.setFailure(e);}return;}if (msg instanceof FullHttpResponse) {FullHttpResponse response = (FullHttpResponse) msg;throw new IllegalStateException("Unexpected FullHttpResponse (getStatus=" + response.status() + ", content="+ response.content().toString(CharsetUtil.UTF_8) + ')');}WebSocketFrame frame = (WebSocketFrame) msg;if (frame instanceof TextWebSocketFrame) {TextWebSocketFrame textFrame = (TextWebSocketFrame) frame;log.info("接收到TXT消息: " + textFrame.text());} else if (frame instanceof PongWebSocketFrame) {log.info("接收到pong消息");} else if (frame instanceof CloseWebSocketFrame) {log.info("接收到closing消息");ch.close();}}@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {// 异常处理log.error("出现异常", cause);if (!handshakeFuture.isDone()) {handshakeFuture.setFailure(cause);}ctx.close();}
}

可以看到，我们这里也要手动标记握手完成，是在自定义的Handler的channelRead0方法中标记的。

测试的时候，我们可以看到，当客户端发送ping的时候，服务端会自动回pong，这个是有Netty实现的服务端自带的心跳机制。

2024-05-25 16:35:10 INFO [WebSocketClientHandler] channelActive, 进行handshake
2024-05-25 16:35:10 INFO [WebSocketClientHandler] websocket Handshake 完成!
123
2024-05-25 16:35:26 INFO [WebSocketClientHandler] 接收到TXT消息: 2024-35-25 04:05:26: 123
ping
2024-05-25 16:35:52 INFO [WebSocketClientHandler] 接收到pong消息