Netty自動重連機制的Demo

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適讀人羣：Java-Netty 初級

Netty自動重連機制

版本：netty 4.1.*

申明：本文旨在從新分享討論Netty官方相關案例，添加部分我的理解與要點解析。

這個是InChat的案例地址，裏面補充了詳細的註釋，比起官方會容易看一點。

官方案例地址：https://netty.io/4.1/xref/io/...

正文

• UptimeClient（客戶端）
• UptimeClientHandler
• UptimeServer（服務端）
• UptimeServerHandler

要點介紹

• IdleStateHandler https://netty.io/4.1/api/io/n...

一個對Channel還沒有執行讀、寫或兩次操做的觸發器

屬性	含義
readerIdleTime	在IdleStateEvent其狀態IdleState.READER_IDLE 時的指定時間段沒有執行讀操做將被觸發。指定0禁用。
writerIdleTime	在IdleStateEvent其狀態IdleState.WRITER_IDLE 時的指定時間段沒有執行寫操做將被觸發。指定0禁用。
allIdleTime	一個IdleStateEvent其狀態IdleState.ALL_IDLE 時的時間在規定的時間進行讀取和寫入都將被觸發。指定0禁用。

以下一個在沒有信息時發送ping消息，且30秒沒有入站信息則關閉鏈接

public class MyChannelInitializer extends ChannelInitializer<Channel> {
      @Override
     public void initChannel(Channel channel) {
         channel.pipeline().addLast("idleStateHandler", new IdleStateHandler(60, 30, 0));
         channel.pipeline().addLast("myHandler", new MyHandler());
     }
 }

 // Handler should handle the IdleStateEvent triggered by IdleStateHandler.
 public class MyHandler extends ChannelDuplexHandler {
      @Override
     public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
         if (evt instanceof IdleStateEvent) {
             IdleStateEvent e = (IdleStateEvent) evt;
             if (e.state() == IdleState.READER_IDLE) {
                 ctx.close();
             } else if (e.state() == IdleState.WRITER_IDLE) {
                 ctx.writeAndFlush(new PingMessage());
             }
         }
     }
 }

項目源碼

• UptimeClient

/**
 * Created by MySelf on 2019/8/27.
 */
public final class UptimeClient {

    static final String HOST = System.getProperty("host", "127.0.0.1");
    static final int PORT = Integer.parseInt(System.getProperty("port", "8080"));
    // 從新鏈接前睡眠5秒
    static final int RECONNECT_DELAY = Integer.parseInt(System.getProperty("reconnectDelay", "5"));
    // 當服務器在 10 秒內不發送任何內容時從新鏈接。
    private static final int READ_TIMEOUT = Integer.parseInt(System.getProperty("readTimeout", "10"));

    private static final UptimeClientHandler handler = new UptimeClientHandler();
    private static final Bootstrap bs = new Bootstrap();

    public static void main(String[] args) throws Exception {
        EventLoopGroup group = new NioEventLoopGroup();
        bs.group(group)
                .channel(NioSocketChannel.class)
                .remoteAddress(HOST,PORT)
                .handler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception {
                        ch.pipeline().addLast(new IdleStateHandler(READ_TIMEOUT,0,0),handler);
                    }
                });
        bs.connect();
    }

    static void connect(){
        bs.connect().addListener(new ChannelFutureListener() {
            @Override
            public void operationComplete(ChannelFuture future) throws Exception {
                if (future.cause() != null){
                    handler.startTime = -1;
                    handler.println("Failed to connect:" + future.cause());
                }
            }
        });
    }

}

• UptimeClientHandler

/**
 * Created by MySelf on 2019/8/27.
 */
@ChannelHandler.Sharable
public class UptimeClientHandler extends SimpleChannelInboundHandler<Object> {

    long startTime = -1;

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {
        //Discard received data
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        if (startTime < 0){
            startTime = System.currentTimeMillis();
        }
        println("Connected to:" + ctx.channel().remoteAddress());
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        println("Disconnected from: " + ctx.channel().remoteAddress());
    }

    @Override
    public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
        if (!(evt instanceof IdleStateEvent)){
            return;
        }
        IdleStateEvent e = (IdleStateEvent)evt;
        if (e.state() == IdleState.READER_IDLE){
            // 鏈接正常，可是沒有讀信息，關閉鏈接
            println("Disconnecting due to no inbound traffic");
            ctx.close();
        }
    }

    @Override
    public void channelUnregistered(ChannelHandlerContext ctx) throws Exception {
        // 睡眠5秒
        println("Sleeping for:" + UptimeClient.RECONNECT_DELAY + 's');
        // 啓動線程從新鏈接
        ctx.channel().eventLoop().schedule(new Runnable() {
            @Override
            public void run() {
                println("Reconnecting to:" + UptimeClient.HOST + ":" + UptimeClient.PORT);
                UptimeClient.connect();
            }
        },UptimeClient.RECONNECT_DELAY, TimeUnit.SECONDS);
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }

    void println(String msg){
        if (startTime < 0){
            System.err.format("[SERVER IS DOWN] %s%n",msg);
        } else {
            System.err.format("[UPTIME: %5ds] %s%n",(System.currentTimeMillis() - startTime)/1000,msg);
        }
    }
}

• UptimeServer

/**
 * Created by MySelf on 2019/8/27.
 */
public final class UptimeServer {

    private static final int PORT = Integer.parseInt(System.getProperty("port", "8080"));
    private static final UptimeServerHandler handler = new UptimeServerHandler();

    private UptimeServer(){}

    public static void main(String[] args) throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup,workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .handler(new LoggingHandler(LogLevel.INFO))
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(handler);
                        }
                    });
            // Bind and start to accept incoming connections.
            ChannelFuture f = b.bind(PORT).sync();

            // Wait until the server socket is closed.
            // In this example, this does not happen, but you can do that to gracefully
            // shut down your server.
            f.channel().closeFuture().sync();
        }finally {
            workerGroup.shutdownGracefully();
            bossGroup.shutdownGracefully();
        }
    }
}

• UptimeServerHandler

/**
 * Created by MySelf on 2019/8/27.
 */
@ChannelHandler.Sharable
public class UptimeServerHandler extends SimpleChannelInboundHandler<Object> {

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        // Close the connection when an exception is raised.
        cause.printStackTrace();
        ctx.close();
    }

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {
        // discard
    }
}