Netty源碼分析（二）----- ServerBootstrap

時間 2019-11-11

標籤 netty 源碼分析 serverbootstrap 欄目 Netty 简体版

原文原文鏈接

BootStrap在netty的應用程序中負責引導服務器和客戶端。netty包含了兩種不一樣類型的引導：
1. 使用服務器的ServerBootStrap，用於接受客戶端的鏈接以及爲已接受的鏈接建立子通道。
2. 用於客戶端的BootStrap，不接受新的鏈接，而且是在父通道類完成一些操做。html

通常服務端的代碼以下所示：java

SimpleServer.javabootstrap

/**
 * Created by chenhao on 2019/9/4.
 */
public final class SimpleServer {

    public static void main(String[] args) throws Exception {
        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .handler(new SimpleServerHandler())
                    .childHandler(new SimpleServerInitializer())
                    .option(ChannelOption.SO_BACKLOG, 128)
                    .childOption(ChannelOption.SO_KEEPALIVE, true);

            ChannelFuture f = b.bind(8888).sync();

            f.channel().closeFuture().sync();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

SimpleServerHandler.java數組

private static class SimpleServerHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("channelActive");
    }

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

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

SimpleServerInitializer.java服務器

public class SimpleServerInitializer extends ChannelInitializer<SocketChannel>{

    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();

        pipeline.addLast("framer", new DelimiterBasedFrameDecoder(8192, Delimiters.lineDelimiter()));
        pipeline.addLast("decoder", new StringDecoder());
        pipeline.addLast("encoder", new StringEncoder());
        pipeline.addLast("handler", new SimpleChatServerHandler());

        System.out.println("SimpleChatClient:" + ch.remoteAddress()+"鏈接上");
    }
}

在上篇博文（Netty源碼分析（一）----- NioEventLoopGroup）中剖析了以下的兩行代碼內部的構造函數中幹了些什麼。ide

EventLoopGroup bossGroup = new NioEventLoopGroup(1);
EventLoopGroup workerGroup = new NioEventLoopGroup();

具體能夠見上篇博文，對於如上的兩行代碼獲得的結論是：函數

１、若是不指定線程數，則線程數爲：CPU的核數*２oop

２、根據線程個數是否爲2的冪次方，採用不一樣策略初始化chooser源碼分析

３、產生nThreads個NioEventLoop對象保存在children數組中。post

能夠理解NioEventLoop就是一個線程，線程NioEventLoop中裏面有以下幾個屬性：

一、NioEventLoopGroup　（在父類SingleThreadEventExecutor中）

二、selector

三、provider

四、thread （在父類SingleThreadEventExecutor中）

更通俗點就是： NioEventLoopGroup就是一個線程池，NioEventLoop就是一個線程。NioEventLoopGroup線程池中有N個NioEventLoop線程。

ServerBootstrap類分析

本篇博文將分析以下幾行代碼裏面作了些什麼。

ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                .channel(NioServerSocketChannel.class)
                .handler(new SimpleServerHandler())
                .childHandler(new SimpleServerInitializer())
                .option(ChannelOption.SO_BACKLOG, 128)
                .childOption(ChannelOption.SO_KEEPALIVE, true);

ServerBootstrap類的繼承結構以下：

該類的參數，有必要列出：

private final Map<ChannelOption<?>, Object> childOptions = new LinkedHashMap<ChannelOption<?>, Object>();
private final Map<AttributeKey<?>, Object> childAttrs = new LinkedHashMap<AttributeKey<?>, Object>();
private volatile EventLoopGroup childGroup;
private volatile ChannelHandler childHandler;

其父類AbstractBootstrap的參數

private volatile EventLoopGroup group;
private volatile ChannelFactory<? extends C> channelFactory;
private volatile SocketAddress localAddress;
private final Map<ChannelOption<?>, Object> options = new LinkedHashMap<ChannelOption<?>, Object>();
private final Map<AttributeKey<?>, Object> attrs = new LinkedHashMap<AttributeKey<?>, Object>();
private volatile ChannelHandler handler;

下面主要看下這個鏈式設置相關的參數。

group(bossGroup, workerGroup)

public ServerBootstrap group(EventLoopGroup parentGroup, EventLoopGroup childGroup) {
    super.group(parentGroup);
    if (childGroup == null) {
        throw new NullPointerException("childGroup");
    }
    if (this.childGroup != null) {
        throw new IllegalStateException("childGroup set already");
    }
    this.childGroup = childGroup;
    return this;
}

即將workerGroup保存在 ServerBootstrap對象的childGroup屬性上。 bossGroup保存在ServerBootstrap對象的group屬性上

channel(NioServerSocketChannel.class)

public B channel(Class<? extends C> channelClass) {
    if (channelClass == null) {
        throw new NullPointerException("channelClass");
    }
    return channelFactory(new BootstrapChannelFactory<C>(channelClass));
} 
public B channelFactory(ChannelFactory<? extends C> channelFactory) {
    if (channelFactory == null) {
        throw new NullPointerException("channelFactory");
    }
    if (this.channelFactory != null) {
        throw new IllegalStateException("channelFactory set already");
    }

    this.channelFactory = channelFactory;
    return (B) this;
}

函數功能：設置父類屬性channelFactory 爲： BootstrapChannelFactory類的對象。其中這裏BootstrapChannelFactory對象中包括一個clazz屬性爲：NioServerSocketChannel.class，從以下該類的構造函數中能夠明顯的獲得這一點。

private static final class BootstrapChannelFactory<T extends Channel> implements ChannelFactory<T> {
    private final Class<? extends T> clazz;

    BootstrapChannelFactory(Class<? extends T> clazz) {
        this.clazz = clazz;
    }

    @Override
    public T newChannel() {
        try {
            return clazz.newInstance();
        } catch (Throwable t) {
            throw new ChannelException("Unable to create Channel from class " + clazz, t);
        }
    }

    @Override
    public String toString() {
        return StringUtil.simpleClassName(clazz) + ".class";
    }
}

而且BootstrapChannelFactory中提供 newChannel()方法，咱們能夠看到 clazz.newInstance()，主要是經過反射來實例化NioServerSocketChannel.class

handler(new SimpleServerHandler())

public B handler(ChannelHandler handler) {
    if (handler == null) {
        throw new NullPointerException("handler");
    }
    this.handler = handler; return (B) this;
}

注意：這裏的handler函數的入參類是咱們本身提供的。以下，後面的博文中將會分析這個handler將會在哪裏以及什麼時候被調用，這裏只須要記住這一點便可

private static class SimpleServerHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("channelActive");
    }

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

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

childHandler(new SimpleServerInitializer())

public ServerBootstrap childHandler(ChannelHandler childHandler) {
    if (childHandler == null) {
        throw new NullPointerException("childHandler");
    }
    this.childHandler = childHandler;
    return this;
}

由最後一句可知，其實就是講傳入的childHandler賦值給ServerBootstrap的childHandler屬性。

該函數的主要做用是設置channelHandler來處理客戶端的請求的channel的IO。這裏咱們通常都用ChannelInitializer這個類的實例或則繼承自這個類的實例
這裏我是經過新建類SimpleChatServerInitializer繼承自ChannelInitializer。具體的代碼以下：

public class SimpleChatServerInitializer extends ChannelInitializer<SocketChannel>{

    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();

        pipeline.addLast("framer", new DelimiterBasedFrameDecoder(8192, Delimiters.lineDelimiter()));
        pipeline.addLast("decoder", new StringDecoder());
        pipeline.addLast("encoder", new StringEncoder());
        pipeline.addLast("handler", new SimpleChatServerHandler());

        System.out.println("SimpleChatClient:" + ch.remoteAddress()+"鏈接上");
    }
}

咱們再看看ChannelInitializer這個類的繼承圖可知ChannelInitializer其實就是繼承自ChannelHandler的

可知，這個類其實就是往pipeline中添加了不少的channelHandler。

配置ServerBootstrap的option

這裏調用的是父類的AbstractBootstrap的option()方法，源碼以下：

public <T> B option(ChannelOption<T> option, T value) {
    if (option == null) {
        throw new NullPointerException("option");
    }
    if (value == null) {
        synchronized (options) {
            options.remove(option);
        }
    } else {
        synchronized (options) {
            options.put(option, value);
        }
    }
    return (B) this;
}

其中最重要的一行代碼就是：
options.put(option, value);
這裏用到了options這個參數，在AbstractBootstrap的定義以下：
private final Map<ChannelOption<?>, Object> options = new LinkedHashMap<ChannelOption<?>, Object>();
可知是私有變量，並且是一個Map集合。這個變量主要是設置TCP鏈接中的一些可選項,並且這些屬性是做用於每個鏈接到服務器被建立的channel。

配置ServerBootstrap的childOption

這裏調用的是父類的ServerBootstrap的childOption()方法，源碼以下：

public <T> ServerBootstrap childOption(ChannelOption<T> childOption, T value) {
    if (childOption == null) {
        throw new NullPointerException("childOption");
    }
    if (value == null) {
        synchronized (childOptions) {
            childOptions.remove(childOption);
        }
    } else {
        synchronized (childOptions) {
            childOptions.put(childOption, value);
        }
    }
    return this;
}