netty源碼解析(4.0)-11 Channel NIO實現-概覽

結構設計

　　Channel的NIO實現位於io.netty.channel.nio包和io.netty.channel.socket.nio包中，其中io.netty.channel.nio是抽象實現，io.netty.channel.socket.nio最終實現。下面是Channel NIO相關類的派生圖:

　　NIO實現最終派生出3個類型NioServerSocketChannel實現了tcp server, NioSocketChannel實現了tcp client, NioDatagramChannel實現了udp socket。

　　整個NIO實現分爲三個層次:

　　AbstractNioChannel抽象層

　　對channel進行基本的初始化工作，把channel設置成非阻塞模式。

　　實現Channel.Unsafe的connect方法框架，提供給了doConnection, doFinishConnect兩個抽象方法，把真正的連接操作交給子類實現。

　　覆蓋了AbstractChannel的doRegister，doDeregister方法，正兩個方法實現了Channel的selectionKey的註冊和註銷。

　　實現AbstractChannel的doClose, 這個方法並沒有真正關閉channel動作。

　　形如doXXX的方法是，AbstractChannel提供的擴展點，在<<netty源碼解解析(4.0)-3 Channel的抽象實現>>的末尾，給出了這些擴展點的詳細列表。

　　AbstractNioByteChannel, AbstractNioMessageChannel抽象層

　　這兩個類主要實現read和write的框架，它們的實現大致相同AbstractNioByteChannel讀寫的是byte array，而AbstractNioMessageChannel讀的時候會把byte array轉換成結構化的對象，寫的時候把結構化對象序列化成byte array。

　　AbstractNioByteChannel定義了3個抽象方法用來實現真正的讀寫操作: doReadBytes, doWriteBytes, doWriteFileRegion。

　　AbstractNioMessageChannel第了兩個2個抽象方法用來實現真正的結構化數據類型的讀寫: doReadMessages, doWriteMessage。

　　NioServerSocketChannel, NioSocketChannel, NioDatagramChannel最終實現

　　封裝NIO API調用，真正的I/O操操作和socket相關的api調用都在這一層實現。　　

　　使用方式

　　使用過netty的人都知道，netty提供了ServerBootstrap和Bootstrap類幫助用戶方便地創建服務器端和客戶端應用，但這不是必須的。僅僅使用NioServerSocketChannel, NioSocketChannel, NioDatagramChannel和NioEventLoopGroup就可以用開發tcp的server和client, 及udp應用。

　　爲了能讓讀者能夠更清晰地理解NioEventLoopGroup和Channel直接的關係，下面給出了最原始的使用使用netty框架的代碼。

　　tcp server實現

 1 import io.netty.buffer.ByteBuf;
 2 import io.netty.channel.*;
 3 import io.netty.channel.nio.NioEventLoopGroup;
 4 import io.netty.channel.socket.nio.NioServerSocketChannel;
 5 
 6 import java.net.InetSocketAddress;
 7 import java.nio.charset.Charset;
 8 
 9 public class TcpServer {
10     private NioEventLoopGroup group = new NioEventLoopGroup();
11 
12     public static void main(String[] argc){
13         TcpServer server = new TcpServer();
14         server.start();
15 
16         while(true){
17             try{
18                 Thread.sleep(1000);
19             }catch (Exception e){
20                 break;
21             }
22         }
23 
24         server.stop();
25     }
26 
27     public void start(){
28         NioServerSocketChannel server = new NioServerSocketChannel();
29 
30         ChannelPipeline pipleline = server.pipeline();
31         pipleline.addFirst(new ServerHandler());
32 
33         group.register(server).addListener(new ChannelFutureListener() {
34             @Override
35             public void operationComplete(ChannelFuture future) throws Exception {
36                 server.bind(new InetSocketAddress(9001));
37                 System.out.println("server listen add:"+9001);
38             }
39         });
40     }
41     public void stop(){
42         group.shutdownGracefully();
43     }
44 
45     private class ServerHandler extends ChannelInboundHandlerAdapter{
46 
47         @Override
48         public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception{
49             Channel child = (Channel)msg;
50 
51             child.pipeline().addLast(new ChildHandler());
52 
53             group.register(child);
54 
55         }
56     }
57 
58     private class ChildHandler extends ChannelInboundHandlerAdapter{
59 
60         @Override
61         public void channelActive(ChannelHandlerContext ctx) throws Exception {
62             System.out.println("connected");
63         }
64 
65         @Override
66         public void channelInactive(ChannelHandlerContext ctx) throws Exception {
67             System.out.println("closed");
68         }
69 
70         @Override
71         public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception{
72             Channel chnl = ctx.channel();
73             ByteBuf data = (ByteBuf)msg;
74 
75             System.out.println("recv: "+data.toString(Charset.forName("utf-8")));
76             chnl.write(msg);
77         }
78 
79         @Override
80         public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
81             ctx.channel().flush();
82         }
83 
84     }
85 }

　　一個channel創建之後，首先要做的事就是向pipleline中添加handler，然後纔是把它註冊到NioEventLoopGroup中(第31，33行)。這個順序不能錯，否則，handler的handlerAdded，channelRegistered和channelActive將不會被調用。當NioServerSocketChannel收到一個連接時，ServerHandler的的channelRead方法將會被調用，的新建好的連接當成參數傳遞進來，第49-53行是對新連接的初始化代碼。

　　tcp client實現

import io.netty.buffer.ByteBuf;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;

import java.net.InetSocketAddress;
import java.nio.charset.Charset;

public class TcpClient {

    public static void main(String[] args){
        NioEventLoopGroup group = new NioEventLoopGroup();

        NioSocketChannel client = new NioSocketChannel();
        client.pipeline().addLast(new ClientInboundHandler());

        group.register(client);

        client.connect(new InetSocketAddress(9001));

        try{
            Thread.sleep(3000);
        }catch (Exception e){

        }
        group.shutdownGracefully();
    }

    private static class ClientInboundHandler extends ChannelInboundHandlerAdapter{
        @Override
        public void channelActive(ChannelHandlerContext ctx) throws Exception {
            System.out.println("connected");
            Channel chnl = ctx.channel();
            ByteBuf buf = chnl.alloc().buffer();
            buf.writeBytes( "this is test".getBytes());
            chnl.writeAndFlush(buf);
        }

        @Override
        public void channelInactive(ChannelHandlerContext ctx) throws Exception {
            System.out.println("closed");
        }

        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception{
            ByteBuf data = (ByteBuf)msg;
            System.out.println("recv: "+data.toString(Charset.forName("utf-8")));
            ctx.channel().close();
        }
    }

}

　　client的實現比server實現相對簡單，添加handler，register順序和server一致。只有把一個channel註冊到gruop中之後才能調用它的方法，應爲channel的大多數方法都需要通過pipleline調用，而pipleline需要在eventLoop中執行。

　　udp沒有server和client的區別，這裏爲了使代碼更加清晰，把server和client代碼區分開來。

　　udp server

import io.netty.buffer.ByteBuf;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.DatagramPacket;
import io.netty.channel.socket.nio.NioDatagramChannel;

import java.net.InetSocketAddress;
import java.nio.charset.Charset;

public class UdpServer {

    public static void main(String[] args){
        NioEventLoopGroup group = new NioEventLoopGroup();

        NioDatagramChannel chnl = new NioDatagramChannel();
        chnl.pipeline().addLast(new UdpHandler());

        group.register(chnl).addListener(new ChannelFutureListener() {
            @Override
            public void operationComplete(ChannelFuture future) throws Exception {
                chnl.bind(new InetSocketAddress(9002));
                System.out.println("udp bind at:"+9002);
            }
        });

        while(true){
            try{
                Thread.sleep(1000);
            }catch (Exception e){
                break;
            }
        }
        group.shutdownGracefully();
    }
    private static class UdpHandler extends ChannelInboundHandlerAdapter {

        @Override
        public void channelActive(ChannelHandlerContext ctx) throws Exception {
            System.out.print("udp channel active");
        }

        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception{
            Channel chnl = ctx.channel();
            DatagramPacket pkg = (DatagramPacket)msg;
            ByteBuf content = pkg.content();
            InetSocketAddress from = pkg.sender();
            System.out.println("recv: "+content.toString(Charset.forName("utf-8"))+" from:"+from.toString());
            pkg = new DatagramPacket(content, from);
            chnl.write(pkg);
        }

        @Override
        public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
            ctx.channel().flush();
        }
    }
}

　　udp client

import io.netty.buffer.ByteBuf;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.DatagramPacket;
import io.netty.channel.socket.nio.NioDatagramChannel;

import java.net.InetSocketAddress;
import java.nio.charset.Charset;

public class UdpClient {

    public static void main(String[] args){
        NioEventLoopGroup group = new NioEventLoopGroup();

        NioDatagramChannel chnl = new NioDatagramChannel();
        chnl.pipeline().addLast(new UdpHandler());

        group.register(chnl).addListener(new ChannelFutureListener() {
            @Override
            public void operationComplete(ChannelFuture future) throws Exception {
                chnl.bind(new InetSocketAddress(0));
            }
        });

        try{
            Thread.sleep(3000);
        }catch (Exception e){
        }
        group.shutdownGracefully();
    }

    private static class UdpHandler extends ChannelInboundHandlerAdapter {

        @Override
        public void channelActive(ChannelHandlerContext ctx) throws Exception {
            System.out.print("udp channel active");
            Channel chnl = ctx.channel();
            ByteBuf content = chnl.alloc().buffer();
            content.writeBytes("udp message".getBytes());
            chnl.writeAndFlush(new DatagramPacket(content, new InetSocketAddress("127.0.0.1", 9002)));
            System.out.println("send message");
        }

        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception{
            DatagramPacket pkg = (DatagramPacket)msg;
            ByteBuf content = pkg.content();
            InetSocketAddress from = pkg.sender();
            System.out.println("recv: "+content.toString(Charset.forName("utf-8"))+" from:"+from.toString());
        }
    }
}

　　NioDatagramChannel和NioSocketChannel的初始化過程大致相同。它們的不同點是，NioSocketChannel在connect之後處於active狀態，NioDatagramChannel是在bind之後處於才處於active狀態。

netty源碼解析(4.0)-11 Channel NIO實現-概覽

netty源碼解析(4.0)-20 ChannelHandler: 自己實現一個自定義協議的服務器和客戶端

netty源碼解析(4.0)-11 Channel NIO實現-概覽

netty源碼解析(4.0)-23 ByteBuf內存管理:分配和釋放

netty源碼解析(4.0)-27 ByteBuf內存池:PoolArena-PoolThreadCache

netty源碼解析(4.0)-16 ChannelHandler概覽

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