Netty Client重连实现

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:

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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:

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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:

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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
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