Netty簡介

1. what

Netty is an asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers & clients.
架構(gòu)圖：


image.png

2. when

2.1 RPC框架
2.2 IM系統(tǒng)
2.3 游戲后端服務(wù)器

3. why

It greatly simplifies and streamlines network programming such as TCP and UDP socket server.

4. how

一個簡單的Discard服務(wù)：

/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.example.discard;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.example.util.ServerUtil;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import io.netty.handler.ssl.SslContext;

/**
 * Discards any incoming data.
 */
public final class DiscardServer {

    static final int PORT = Integer.parseInt(System.getProperty("port", "8009"));

    public static void main(String[] args) throws Exception {
        // Configure SSL.
        final SslContext sslCtx = ServerUtil.buildSslContext();

        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        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
                 public void initChannel(SocketChannel ch) {
                     ChannelPipeline p = ch.pipeline();
                     if (sslCtx != null) {
                         p.addLast(sslCtx.newHandler(ch.alloc()));
                     }
                     p.addLast(new DiscardServerHandler());
                 }
             });

            // 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();
        }
    }
}


/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.example.discard;

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

/**
 * Handles a server-side channel.
 */
public class DiscardServerHandler extends SimpleChannelInboundHandler<Object> { // (1)

    @Override
    public void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {  // (2)
        // discard
        System.out.println("discard...");
    }

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


/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.example.discard;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.example.util.ServerUtil;
import io.netty.handler.ssl.SslContext;

/**
 * Keeps sending random data to the specified address.
 */
public final class DiscardClient {

    static final String HOST = System.getProperty("host", "127.0.0.1");
    static final int PORT = Integer.parseInt(System.getProperty("port", "8009"));
    static final int SIZE = Integer.parseInt(System.getProperty("size", "256"));

    public static void main(String[] args) throws Exception {
        // Configure SSL.
        final SslContext sslCtx = ServerUtil.buildSslContext();

        EventLoopGroup group = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(group)
             .channel(NioSocketChannel.class)
             .handler(new ChannelInitializer<SocketChannel>() {
                 @Override
                 protected void initChannel(SocketChannel ch) throws Exception {
                     ChannelPipeline p = ch.pipeline();
                     if (sslCtx != null) {
                         p.addLast(sslCtx.newHandler(ch.alloc(), HOST, PORT));
                     }
                     p.addLast(new DiscardClientHandler());
                 }
             });

            // Make the connection attempt.
            ChannelFuture f = b.connect(HOST, PORT).sync();

            // Wait until the connection is closed.
            f.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully();
        }
    }
}


/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.example.discard;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;

/**
 * Handles a client-side channel.
 */
public class DiscardClientHandler extends SimpleChannelInboundHandler<Object> {

    private ByteBuf content;
    private ChannelHandlerContext ctx;

    @Override
    public void channelActive(ChannelHandlerContext ctx) {
        this.ctx = ctx;

        // Initialize the message.
        content = ctx.alloc().directBuffer(DiscardClient.SIZE).writeZero(DiscardClient.SIZE);

        // Send the initial messages.
        generateTraffic();
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) {
        content.release();
    }

    @Override
    public void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {
        // Server is supposed to send nothing, but if it sends something, discard it.
    }

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

    long counter;

    private void generateTraffic() {
        // Flush the outbound buffer to the socket.
        // Once flushed, generate the same amount of traffic again.
        ctx.writeAndFlush(content.retainedDuplicate()).addListener(trafficGenerator);
    }

    private final ChannelFutureListener trafficGenerator = new ChannelFutureListener() {
        @Override
        public void operationComplete(ChannelFuture future) {
            if (future.isSuccess()) {
                generateTraffic();
            } else {
                future.cause().printStackTrace();
                future.channel().close();
            }
        }
    };
}
1. nioEventLoopGroup是處理io操作的多線程事件循環(huán)

we are implementing a server-side application in this example, and therefore two NioEventLoopGroup will be used. The first one, often called 'boss', accepts an incoming connection. The second one, often called 'worker', handles the traffic of the accepted connection once the boss accepts the connection and registers the accepted connection to the worker

2. ServerBootStrap

netty的server啟動幫助類

3. NioServerSocketChannel

use the NioServerSocketChannel class which is used to instantiate a new Channel to accept incoming connections.

4. ChannelInitializer

help a user configure a new Channel
configure the ChannelPipeline of the new Channel

Congratulations! You've just finished your first server on top of Netty.

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