本文基于Nett4.0.26.Final版本浅析Client与Server端通讯，先看服务器端：
public class Server { public static void run(int port) { /**Netty创建ServerSocketChannel,默认SelectionKey.OP_ACCEPT*/ EventLoopGroup boss = new NioEventLoopGroup(); EventLoopGroup worker = new NioEventLoopGroup(); try { ServerBootstrap bootstrap = new ServerBootstrap(); bootstrap.group(boss, worker) .channel(NioServerSocketChannel.class) // 设置Channel Type .option(ChannelOption.SO_BACKLOG, 1024) // 设置Channel属性 .childHandler(new ChannelInitializer<SocketChannel>() { @Override protected void initChannel(SocketChannel ch) throws Exception { ChannelPipeline pipeline = ch.pipeline(); pipeline.addLast("frameDecoder", new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE, 0, 4, 0, 4)); pipeline.addLast("frameEncoder", new LengthFieldPrepender(4)); pipeline.addLast("decoder", new StringDecoder(CharsetUtil.UTF_8)); pipeline.addLast("encoder", new StringEncoder(CharsetUtil.UTF_8)); pipeline.addLast(new SimpleChannelHandler()); } }); /**服务器端绑定监听端口并对Channel进行初始化 * 1-ChannelConfig由ChannelOption初始化 * 2-ChannelPipeline(默认DefaultChannelPipeline)添加ChannelHandler * 3-注册Channel并添加监听器ChannelFutureListener.CLOSE_ON_FAILURE * 以异步的方式等待上述操作的完成 * */ ChannelFuture channelFuture = bootstrap.bind(port).sync(); if (channelFuture.isDone()) { System.out.println(String.format("server bind port %s sucess", port)); } /**CloseFuture异步方式关闭*/ channelFuture.channel().closeFuture().sync(); } catch (InterruptedException e) { e.printStackTrace(); } finally { boss.shutdownGracefully(); worker.shutdownGracefully(); } } public static void main(String []args) { Server.run(8080); } } public class SimpleChannelHandler implements ChannelInboundHandler { private static final Gson GSON = new GsonBuilder().create(); /** * the method called when new connect come * */ public void handlerAdded(ChannelHandlerContext ctx) throws Exception { System.out.println(String.format("last channel handler [%s] add", ctx.pipeline().last().getClass().getSimpleName())); } /** * the method called when client close connect * */ public void handlerRemoved(ChannelHandlerContext ctx) throws Exception { ctx.disconnect(ctx.newPromise()); ctx.close(); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { cause.printStackTrace(); } /** * register port for connect channel * */ public void channelRegistered(ChannelHandlerContext ctx) throws Exception { String connect = ctx.channel().remoteAddress().toString().substring(1); System.out.println(String.format("remote connecter address %s", connect)); } @Override public void channelUnregistered(ChannelHandlerContext ctx) throws Exception { } @Override public void channelActive(ChannelHandlerContext ctx) throws Exception { } @Override public void channelInactive(ChannelHandlerContext ctx) throws Exception { } @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { Request req = GSON.fromJson(String.valueOf(msg), Request.class); String json = GSON.toJson(new Response(String.format("server get client status [%s]", req.getStatus()), new Random().nextInt(10))); ctx.write(json); } @Override public void channelReadComplete(ChannelHandlerContext ctx) throws Exception { ctx.flush(); } @Override public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception { } @Override public void channelWritabilityChanged(ChannelHandlerContext ctx) throws Exception { } }
服务器端的ChannelHandler的handlerRemoved方法是当客户端关闭链接时该方法被触发，服务器应当关闭当前与客户端的连接，完成TCP的四次挥手过程。
客户端的实现：
public class Client {
public static void run(String host, int port) {
EventLoopGroup group = new NioEventLoopGroup();
try {
Bootstrap bootstrap = new Bootstrap();
bootstrap.group(group)
.channel(NioSocketChannel.class)
.option(ChannelOption.TCP_NODELAY, true)
.handler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast("frameDecoder", new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE, 0, 4, 0, 4));
pipeline.addLast("frameEncoder", new LengthFieldPrepender(4));
pipeline.addLast("decoder", new StringDecoder(CharsetUtil.UTF_8));
pipeline.addLast("encoder", new StringEncoder(CharsetUtil.UTF_8));
pipeline.addLast(new SimpleClientChannelHandler());
}
});
/**客户端向服务器发起连接请求
* 1-ChannelConfig由ChannelOption初始化
* 2-ChannelPipeline(默认DefaultChannelPipeline)添加ChannelHandler
* 3-注册Channel并添加监听器ChannelFutureListener.CLOSE_ON_FAILURE
* 以异步的方式等待上述操作的完成
* */
ChannelFuture channelFuture = bootstrap.connect(host, port).sync();
if (channelFuture.isSuccess()) {
System.out.println(String.format("connect server(%s:%s) sucess", host, port));
}
channelFuture.channel().closeFuture().sync();
System.out.println("client close sucess");
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
group.shutdownGracefully();
}
}
public static void main(String []args) {
for (int i = 0 ; i < 3 ; ++i) {
Client.run("127.0.0.1", 8080);
System.out.println();
}
// Client.run("127.0.0.1", 8080);
}
}
public class SimpleClientChannelHandler implements ChannelInboundHandler{
private static final Gson GSON = new GsonBuilder().create();
/**
* the method called when client add channel handler(1)
* */
public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
ChannelHandler channelHandler = ctx.channel().pipeline().last();
System.out.println("client last channel handle " + channelHandler.getClass().getSimpleName());
}
/**
* the method called when server disconnect
* */
public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
Channel ch = ctx.channel();
SocketAddress local = ch.localAddress();
SocketAddress remote = ch.remoteAddress();
System.out.println(String.format("server(%s) diconnect and client(%s) close connect", remote.toString().substring(1), local.toString().substring(1)));
ctx.close();
}
/**
* the method called for register port before connect server(2)
* */
public void channelRegistered(ChannelHandlerContext ctx) throws Exception {
System.out.println("client start to register port");
}
@Override
public void channelUnregistered(ChannelHandlerContext ctx) throws Exception {
}
/**
* the method called when channel active(3)
* */
public void channelActive(ChannelHandlerContext ctx) throws Exception {
String json = GSON.toJson(new Request("client status", new Random().nextInt(10)));
ctx.writeAndFlush(json);
System.out.println(String.format("connect established and send to server message [%s]", json));
}
@Override
public void channelInactive(ChannelHandlerContext ctx) throws Exception {
}
/**
* close after receive response from server(server also should close connect)
* */
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
System.out.println(String.format("client receive message [%s]", String.valueOf(msg)));
ctx.disconnect(ctx.newPromise());
}
@Override
public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
System.out.println("77777");
}
@Override
public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
System.out.println("88888");
}
@Override
public void channelWritabilityChanged(ChannelHandlerContext ctx) throws Exception {
System.out.println("99999");
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
cause.printStackTrace();
}
}
在客户端的ChannelHandler中有几个关键方法：
channelActive方法：客户端与服务器建立连接且Channel被激活时该方法被调用，本文在客户端与服务器端建立连接就绪时向服务器发送数据
channelRead方法：当服务器端有数据发送时方法被调用，本文在收到服务器端响应时关闭当前连接(此时服务器端的handlerRemoved方法被调用)
handlerRemoved方法：当服务器确认断开连接时该方法被调用，客户端应关闭Channel(TCP四次挥手结束)
