Netty 教程

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;

import java.net.InetSocketAddress;

/**
 * echo server，接收打印client发送过来的数据，并把数据返回给client
 */
public final class EchoServer {

    static final int PORT = Integer.parseInt(System.getProperty("port", "8007"));

    public static void main(String[] args) throws Exception {

        // 配置服务器
        // 主event loop，负责接受（accept）socket连接
        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        // 从event loop，负责处理socket的事件
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        // server 的channel处理器
        final EchoServerHandler serverHandler = new EchoServerHandler();
        try {
            // Server引导器（配置器）
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    // 设置ip地址和端口，server默认使用本地ip，也可以通过bind()来设置
                    .localAddress(new InetSocketAddress(PORT))
                    // 配置网络传输参数，例如缓存大小
                    .option(ChannelOption.SO_BACKLOG, 100)
                    // 配置日志打印
                    .handler(new LoggingHandler(LogLevel.INFO))
                    // netty核心组件，pipeline 处理器
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        public void initChannel(SocketChannel ch) throws Exception {
                            // 通过channel获取管道对象
                            ChannelPipeline pipeline = ch.pipeline();
                            // 通过管道挂在handler
                            pipeline.addLast(serverHandler);
                        }
                    });

            // 绑定设置的断开（PORT），并阻塞（sync）到绑定完成，绑定完成后就开始监听close信号
            ChannelFuture f = b.bind().sync();

            // 阻塞到接收client发过来关闭（close）信号
            f.channel().closeFuture().sync();
            // 当client发过来close信号后，才会执行这里
        } finally {
            // 关闭所有event loop的线程，并关闭内部的线程
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

}

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandler.Sharable;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import java.nio.charset.StandardCharsets;

/**
 * Handler implementation for the echo server.
 */
@Sharable
public class EchoServerHandler extends ChannelInboundHandlerAdapter {

    /**  第一次建立连接调用 */
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        final char[] chars = "hello client, I am Server.".toCharArray();
        // 建立连接想client发送一句话
        ctx.pipeline().writeAndFlush(Unpooled.copiedBuffer(chars, StandardCharsets.UTF_8));
    }

    /** 客户端发送过来数据调用 */
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) {
        final ByteBuf buf = (ByteBuf) msg;
        String recv = "接收：" + buf.toString(StandardCharsets.UTF_8);
        if(recv.indexOf("exit") != -1){
            ctx.close();
            return;
        }
        System.out.print(recv);
        // 将数据传回客户端
        ctx.write(Unpooled.copiedBuffer(recv.getBytes(StandardCharsets.UTF_8)));
    }

    /** 读取完毕，完成一次读事件 */
    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) {
        // flush - 冲刷数据，flush一次便会触发一次或多次client的read事件，反之server也是
        ctx.flush();
    }

    /** 捕获异常 */
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
        // 引发异常时关闭连接会
        cause.printStackTrace();
        ctx.close();
    }

}

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.Unpooled;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;

import java.nio.charset.StandardCharsets;
import java.util.Scanner;

/**
 * 启动client，可以想server发送消息。server的console可以查看client发送的消息。
 */
public final class EchoClient {

    static final String HOST = System.getProperty("host", "127.0.0.1");
    static final int PORT = Integer.parseInt(System.getProperty("port", "8007"));

    public static void main(String[] args) throws Exception {
        // 配置客户端
        // client工作线程，每一个线程将和一个EventLoop绑定
        EventLoopGroup group = new NioEventLoopGroup();
        try {
            // 客户端引导其
            Bootstrap b = new Bootstrap();
            //配置client启动参数
            b.group(group)
                    // 配置数据通道，不同的数据通道决定了IO的方式，例如Nio开头的是非阻塞IO、Oio的是阻塞IO
                    .channel(NioSocketChannel.class)
                    // 网络传输的参数，例如网络缓存缓存的大小、是否延迟
                    .option(ChannelOption.TCP_NODELAY, true)
                    // 入站、出站处理器
                    // initializer是在入站只执行一次的处理器
                    // 它用来与server建立连接、并在pipeline上挂载编解码处理器、自定义处理器
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        public void initChannel(SocketChannel ch) throws Exception {
                            ChannelPipeline p = ch.pipeline();
                            //p.addLast(new LoggingHandler(LogLevel.INFO));
                            p.addLast(new EchoClientHandler());
                        }
                    });

            // 与server建立连接（connect），并阻塞（sync）到连接建立
            ChannelFuture f = b.connect(HOST, PORT).sync();
            // 获取建立的连接
            final Channel clientChannel = f.channel();

            System.out.println("input 'exit' to EXIT.");
            Scanner sc = new Scanner(System.in);
            String str;
            // 读取并向server发送数据
            while (!(str = sc.next()).startsWith("exit")) {
                clientChannel.writeAndFlush(Unpooled.copiedBuffer(str.toCharArray(), StandardCharsets.UTF_8));
            }
            // 想server发送断开连接的信号
            clientChannel.close();
            // 获取关闭连接后的结果（future），并阻塞（sync）到接收到server发过来的断开连接信号
            clientChannel.closeFuture().sync();
        } finally {
            // 关闭所有的EventLoop，并终止内部的线程
            group.shutdownGracefully();
        }
    }
}

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;

import java.nio.charset.StandardCharsets;

/**
 * client 端 handler
 */
public class EchoClientHandler extends ChannelInboundHandlerAdapter {

    private final ByteBuf firstMessage;

    public EchoClientHandler() {
        firstMessage = Unpooled.copiedBuffer("start data transfer.\n".toCharArray(), StandardCharsets.UTF_8);
    }

    /**
     * 建立连接向server发送一个消息
     */
    @Override
    public void channelActive(ChannelHandlerContext ctx) {
        ctx.writeAndFlush(firstMessage);
    }

    /**
     * client的读事件触发会调用此方法
     */
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) {
        System.out.println("client recv : " + ((ByteBuf) msg).toString(StandardCharsets.UTF_8));
    }

    /**
     * 读取完毕向网络发送数据，flush会触发server的read事件
     */
    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) {
        ctx.flush();
    }

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

}

      public class SquareDecoder extends {@link ByteToMessageDecoder} {
          @Override
          public void decode(ChannelHandlerContext ctx,  ByteBuf in, List<Object> out)
                  throws  Exception {
              out.add(in.readBytes(in.readableBytes()));
          }
      }

       public class StringHandler extends SimpleChannelInboundHandler<String> {
            @Override
           protected void channelRead0(ChannelHandlerContext ctx, String message)
                   throws Exception {
               System.out.println(message);
           }
       }

    public static class InboundHandler extends ChannelInboundHandlerAdapter {
        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
            // 处理异常
            System.err.println(this.getClass().getSimpleName() + " ---- " + cause.getMessage());
            // 向下一个handler传递异常
            ctx.fireExceptionCaught(cause);
        }
    }

            ctx.executor().schedule(()->{
                channelFuture.addListener(new ChannelFutureListener() {
                    @Override
                    public void operationComplete(ChannelFuture future) throws Exception {
                        System.out.println("writeAndFlush done.");
                        if(future.isSuccess()){
                            System.out.println("send success.");
                        }else{
                       		// 处理异常
                            System.out.println("send fail!");
                        }
                    }
                });
            }, 0, TimeUnit.SECONDS);

    private void invokeExceptionCaught(final Throwable cause) {
        if (invokeHandler()) {
            try {
                //
                handler().exceptionCaught(this, cause);
            } catch (Throwable error) {
                if (logger.isDebugEnabled()) {
                    logger.debug(
                        "An exception {}" +
                        "was thrown by a user handler's exceptionCaught() " +
                        "method while handling the following exception:",
                        ThrowableUtil.stackTraceToString(error), cause);
                } else if (logger.isWarnEnabled()) {
                    logger.warn(
                        "An exception '{}' [enable DEBUG level for full stacktrace] " +
                        "was thrown by a user handler's exceptionCaught() " +
                        "method while handling the following exception:", error, cause);
                }
            }
        } else {
            fireExceptionCaught(cause);
        }
    }

    private void invokeChannelActive() {
        if (invokeHandler()) {
            try {
                ((ChannelInboundHandler) handler()).channelInactive(this);
            } catch (Throwable t) {
            	// 处理异常
                invokeExceptionCaught(t);
            }
        } else {
            fireChannelInactive();
        }
    }

    private void invokeChannelRead(Object msg) {
        if (invokeHandler()) {
            try {
                ((ChannelInboundHandler) handler()).channelRead(this, msg);
            } catch (Throwable t) {
            	// 处理异常
                invokeExceptionCaught(t);
            }
        } else {
            fireChannelRead(msg);
        }
    }

   // A special catch-all handler that handles both bytes and messages.
    final class TailContext extends AbstractChannelHandlerContext implements ChannelInboundHandler {

        TailContext(DefaultChannelPipeline pipeline) {
            super(pipeline, null, TAIL_NAME, TailContext.class);
            setAddComplete();
        }

        @Override
        public void userEventTriggered(ChannelHandlerContext ctx, Object evt) {
            onUnhandledInboundUserEventTriggered(evt);
        }

        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
            // 处理最后的异常，方法如下
            onUnhandledInboundException(cause);
        }
        // 省略...
    }

    /**
     * 处理最后的异常
     * Called once a {@link Throwable} hit the end of the {@link ChannelPipeline} without been handled by the user
     * in {@link ChannelHandler#exceptionCaught(ChannelHandlerContext, Throwable)}.
     */
    protected void onUnhandledInboundException(Throwable cause) {
        try {
            logger.warn(
                    "An exceptionCaught() event was fired, and it reached at the tail of the pipeline. " +
                            "It usually means the last handler in the pipeline did not handle the exception.",
                    cause);
        } finally {
            ReferenceCountUtil.release(cause);
        }
    }

    final class HeadContext extends AbstractChannelHandlerContext
            implements ChannelOutboundHandler, ChannelInboundHandler {

        private final Unsafe unsafe;

        HeadContext(DefaultChannelPipeline pipeline) {
            super(pipeline, null, HEAD_NAME, HeadContext.class);
            unsafe = pipeline.channel().unsafe();
            setAddComplete();
        }

        @Override
        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
            ctx.fireExceptionCaught(cause);
        }
        // 省略...
    }

public ScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit)
public <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit)
public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay, long period, TimeUnit unit)
public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay, long delay, TimeUnit unit)

    /**
     * 核心方法，所有暴露的schedule方法最后都调用此方法
     * @param task 可执行的对象（实现Runnable）且具有返回值（实现Future）
     * @return task执行结果，可获取执行结果（success/failure），可以监听状态
     */
    private <V> ScheduledFuture<V> schedule(final ScheduledFutureTask<V> task) {
        // 判断在哪里创建（schedule）定时任务
        if (inEventLoop()) {
            // 在EventLoop线程中
            // 如果是在EventLoop（handler执行上下文）中创建的定时任务，就放到任务执行队列中
            scheduleFromEventLoop(task);
        } else {
            // 在外部线程 e.g. main线程调用schedule创建定时任务

            // 截止时间 （当前 - ScheduleFutureTask创建时间）
            final long deadlineNanos = task.deadlineNanos();
            // 任务提交前回调判断，true 立即执行任务，false 延迟执行
            if (beforeScheduledTaskSubmitted(deadlineNanos)) {
                // execute表示调用执行（立即run），是个未实现的方法，未来由子类实现，由父类调用
                execute(task);
            } else {
                // 在不重写父类lazyExecute时默认仍然使用当前EventLoop线程执行
                lazyExecute(task);
                // 任务提交之后回调，方法返回true唤醒当前EventLoop线程，false不唤醒
                if (afterScheduledTaskSubmitted(deadlineNanos)) {
                    // 官方解释是为了避免线程竞争
                    // WAKEUP_TASK这个任务run方法没有执行的语句，使线程保持活跃（等待->可执行，持有CPU资源），避免线程竞争CPU开销
                    execute(WAKEUP_TASK);
                }
            }
        }
        return task;
    }

    // 在EventLoop中创建的定时任务放在taskQueue, 方便EventGroup调度
	final void scheduleFromEventLoop(final ScheduledFutureTask<?> task) {
        // nextTaskId a long and so there is no chance it will overflow back to 0
        scheduledTaskQueue().add(task.setId(++nextTaskId));
    }

private void doStartThread();
// 执行一个任务
public void execute(Runnable task);
// 关闭
public Future<?> shutdownGracefully(long quietPeriod, long timeout, TimeUnit unit);

    /**
     * The NIO {@link Selector}.
     */
    private Selector selector;
    private Selector unwrappedSelector;
    private SelectedSelectionKeySet selectedKeys;