Netty 自动重连

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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