Netty Client重连实现

from:http://itindex.net/detail/54161-netty-client

当我们用Netty实现一个TCP client时，我们当然希望当连接断掉的时候Netty能够自动重连。 
Netty Client有两种情况下需要重连：

1. Netty Client启动的时候需要重连
2. 在程序运行中连接断掉需要重连。

对于第一种情况，Netty的作者在stackoverflow上给出了 解决方案， 
对于第二种情况，Netty的例子uptime中实现了一种 解决方案。

而Thomas在他的 文章中提供了这两种方式的实现的例子。

实现ChannelFutureListener 用来启动时监测是否连接成功，不成功的话重试：

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

public class Client { private EventLoopGroup loop = new NioEventLoopGroup(); public static void main( String[] args ) { new Client().run(); } public Bootstrap createBootstrap(Bootstrap bootstrap, EventLoopGroup eventLoop) { if (bootstrap != null) { final MyInboundHandler handler = new MyInboundHandler(this); bootstrap.group(eventLoop); bootstrap.channel(NioSocketChannel.class); bootstrap.option(ChannelOption.SO_KEEPALIVE, true); bootstrap.handler(new ChannelInitializer<SocketChannel>() { @Override protected void initChannel(SocketChannel socketChannel) throws Exception { socketChannel.pipeline().addLast(handler); } }); bootstrap.remoteAddress("localhost", 8888); bootstrap.connect().addListener(new ConnectionListener(this)); } return bootstrap; } public void run() { createBootstrap(new Bootstrap(), loop); } }

ConnectionListener 负责重连：

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

public class ConnectionListener implements ChannelFutureListener { private Client client; public ConnectionListener(Client client) { this.client = client; } @Override public void operationComplete(ChannelFuture channelFuture) throws Exception { if (!channelFuture.isSuccess()) { System.out.println("Reconnect"); final EventLoop loop = channelFuture.channel().eventLoop(); loop.schedule(new Runnable() { @Override public void run() { client.createBootstrap(new Bootstrap(), loop); } }, 1L, TimeUnit.SECONDS); } } }

同样在ChannelHandler监测连接是否断掉，断掉的话也要重连：

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

public class MyInboundHandler extends SimpleChannelInboundHandler { private Client client; public MyInboundHandler(Client client) { this.client = client; } @Override public void channelInactive(ChannelHandlerContext ctx) throws Exception { final EventLoop eventLoop = ctx.channel().eventLoop(); eventLoop.schedule(new Runnable() { @Override public void run() { client.createBootstrap(new Bootstrap(), eventLoop); } }, 1L, TimeUnit.SECONDS); super.channelInactive(ctx); } }

参考文档

1. http://stackoverflow.com/questions/19739054/whats-the-best-way-to-reconnect-after-connection-closed-in-netty
2. https://github.com/netty/netty/blob/master/example/src/main/java/io/netty/example/uptime/UptimeClientHandler.java
3. http://tterm.blogspot.jp/2014/03/netty-tcp-client-with-reconnect-handling.html
4. ctx.close vs ctx.channel().close
5. ctx.write vs ctx.channel().write