Netty 自动重连

from: http://www.dozer.cc/2015/05/netty-auto-reconnect.html

自动重连

用 Netty 写 Client 和 Server 的时候必须要去处理自动重连。

Server 端启动时的错误，要去不断重试。

Client 端不仅要处理启动时的错误，还要处理中途断开连接。

Server 端的处理

和常规的代码相比，Server 端只要处理一个地方即可：

public final class TcpServer {         private volatile EventLoopGroup bossGroup;      private volatile EventLoopGroup workerGroup;      private volatile ServerBootstrap bootstrap;      private volatile boolean closed = false;      private final int localPort;      public TcpServer(int localPort) {         this.localPort = localPort;     }      public void close() {         closed = true;          bossGroup.shutdownGracefully();         workerGroup.shutdownGracefully();          System.out.println("Stopped Tcp Server: " + localPort);     }      public void init() {         closed = false;          bossGroup = new NioEventLoopGroup();         workerGroup = new NioEventLoopGroup();         bootstrap = new ServerBootstrap();         bootstrap.group(bossGroup, workerGroup);          bootstrap.channel(NioServerSocketChannel.class);          bootstrap.childHandler(new ChannelInitializer<SocketChannel>() {             @Override             protected void initChannel(SocketChannel ch) throws Exception {                 //todo: add more handler             }         });          doBind();     }      protected void doBind() {         if (closed) {             return;         }          bootstrap.bind(localPort).addListener(new ChannelFutureListener() {             @Override             public void operationComplete(ChannelFuture f) throws Exception {                 if (f.isSuccess()) {                     System.out.println("Started Tcp Server: " + localPort);                 } else {                     System.out.println("Started Tcp Server Failed: " + localPort);                      f.channel().eventLoop().schedule(() -> doBind(), 1, TimeUnit.SECONDS);                 }             }         });     } }

我们把整个初始化分成了两个部分，第一部分是初始化相关 class，第二部分做真正的监听端口。

这里最特殊的地方就是在调用bind方法后，添加一个listener检查是否成功，如果失败的话，需要调用.channel().eventLoop().schedule()方法，创建一个任务，我这代码设置的是1秒后尝试重新连接。

另外考虑到 server 可以被人为关闭，所以还需要检查当前时候已经关闭。如果不检查的话，你的 server 可能就永远也关不掉了。

Client 端的处理

client 端启动流程差不多，但是需要加一个 handler 来处理连接断开。

public class TcpClient {      private volatile EventLoopGroup workerGroup;      private volatile Bootstrap bootstrap;      private volatile boolean closed = false;      private final String remoteHost;      private final int remotePort;      public TcpClient(String remoteHost, int remotePort) {         this.remoteHost = remoteHost;         this.remotePort = remotePort;     }      public void close() {         closed = true;         workerGroup.shutdownGracefully();         System.out.println("Stopped Tcp Client: " + getServerInfo());     }      public void init() {         closed = false;          workerGroup = new NioEventLoopGroup();         bootstrap = new Bootstrap();         bootstrap.group(workerGroup);         bootstrap.channel(NioSocketChannel.class);          bootstrap.handler(new ChannelInitializer<SocketChannel>() {             @Override             public void initChannel(SocketChannel ch) throws Exception {                 ChannelPipeline pipeline = ch.pipeline();                 pipeline.addFirst(new ChannelInboundHandlerAdapter() {                     @Override                     public void channelInactive(ChannelHandlerContext ctx) throws Exception {                         super.channelInactive(ctx);                         ctx.channel().eventLoop().schedule(() -> doConnect(), 1, TimeUnit.SECONDS);                     }                 });                  //todo: add more handler             }         });          doConnect();     }      private void doConnect() {         if (closed) {             return;         }          ChannelFuture future = bootstrap.connect(new InetSocketAddress(remoteHost, remotePort));          future.addListener(new ChannelFutureListener() {             public void operationComplete(ChannelFuture f) throws Exception {                 if (f.isSuccess()) {                     System.out.println("Started Tcp Client: " + getServerInfo());                 } else {                     System.out.println("Started Tcp Client Failed: " + getServerInfo());                     f.channel().eventLoop().schedule(() -> doConnect(), 1, TimeUnit.SECONDS);                 }             }         });     }      private String getServerInfo() {         return String.format("RemoteHost=%s RemotePort=%d",                 remotePort,                 remotePort);     } }

可以看到，我们在channelInactive事件中，也创建了一个任务，在1秒后重新连接。

示例代码

大家可以自己跑跑看：

https://github.com/dozer47528/AutoReconnectNettyExample

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