netty入门03

本文来源：http://blog.csdn.net/zxhoo/article/details/17532857

感谢博主。本文仅供参考学习。

 

目录(?)[+]

这篇文章接着上一篇，分析一下Netty4的ServerBootstrp是如何工作的。

EchoServer

先看看Netty自带的EchoServer例子：

/**
 * Echoes back any received data from a client.
 */
public class EchoServer {

    private final int port;

    public EchoServer(int port) {
        this.port = port;
    }

    public void run() throws Exception {
        // Configure the server.
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
             .channel(NioServerSocketChannel.class)
             .option(ChannelOption.SO_BACKLOG, 100)
             .handler(new LoggingHandler(LogLevel.INFO))
             .childHandler(new ChannelInitializer<SocketChannel>() {
                 @Override
                 public void initChannel(SocketChannel ch) throws Exception {
                     ch.pipeline().addLast(
                             //new LoggingHandler(LogLevel.INFO),
                             new EchoServerHandler());
                 }
             });

            // Start the server.
            ChannelFuture f = b.bind(port).sync();

            // Wait until the server socket is closed.
            f.channel().closeFuture().sync();
        } finally {
            // Shut down all event loops to terminate all threads.
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        int port;
        if (args.length > 0) {
            port = Integer.parseInt(args[0]);
        } else {
            port = 8080;
        }
        new EchoServer(port).run();
    }
}

可以看出，用法和Bootstrap差不多。

作为Builder的ServerBootstrap

public final class ServerBootstrap extends AbstractBootstrap<ServerBootstrap, ServerChannel> {

    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;
    // ...
}

看代码可以知道，ServerBootstrap比它的超类多了四个Part，如下图所示：

从bind()方法入手

bind()方法实际上是在AbstractBootstrap里定义的，bind()先调用validate()方法检查各个Part是否准备就 绪，然后把工作交给了doBind()方法。doBind()方法首先调用initAndRegister()方法，然后把工作交给doBind0()。 initAndRegister()会调用模板方法init()来初始化Channel，initAndRegister()方法的细节上篇文章分析过了，这里不再复述。下面是整个方法调用过程的示意图：

init()方法

@Override
void init(Channel channel) throws Exception {
    final Map<ChannelOption<?>, Object> options = options();
    synchronized (options) {
        channel.config().setOptions(options);
    }

    final Map<AttributeKey<?>, Object> attrs = attrs();
    synchronized (attrs) {
        for (Entry<AttributeKey<?>, Object> e: attrs.entrySet()) {
            @SuppressWarnings("unchecked")
            AttributeKey<Object> key = (AttributeKey<Object>) e.getKey();
            channel.attr(key).set(e.getValue());
        }
    }

    ChannelPipeline p = channel.pipeline();
    if (handler() != null) {
        p.addLast(handler());
    }

    final EventLoopGroup currentChildGroup = childGroup;
    final ChannelHandler currentChildHandler = childHandler;
    final Entry<ChannelOption<?>, Object>[] currentChildOptions;
    final Entry<AttributeKey<?>, Object>[] currentChildAttrs;
    synchronized (childOptions) {
        currentChildOptions = childOptions.entrySet().toArray(newOptionArray(childOptions.size()));
    }
    synchronized (childAttrs) {
        currentChildAttrs = childAttrs.entrySet().toArray(newAttrArray(childAttrs.size()));
    }

    p.addLast(new ChannelInitializer<Channel>() {
        @Override
        public void initChannel(Channel ch) throws Exception {
            ch.pipeline().addLast(new ServerBootstrapAcceptor(
                    currentChildGroup, currentChildHandler, currentChildOptions, currentChildAttrs));
        }
    });
}

ServerBootstrap类的init()方法虽然很长，但是却不难理解。首先是给Channel设置options和attrs，然后把User 提供的针对NioServerSocketChannel的Handler添加到Pipeline的末尾。接下来复制childOptions和 childAttrs，最后实例化一个ChannelInitializer，添加到Pipeline的末尾。init()方法执行完毕之 后，AbstractBootstrap的initAndRegister()方法会将NioServerSocketChannel注册到group 里。到此为止，NioServerSocketChannel的状态如下图所示：

ChannelInitializer在channelRegistered事件触发后会调用initChannel()方法，随后把自己从Pipeline里删除：

@Sharable
public abstract class ChannelInitializer<C extends Channel> extends ChannelInboundHandlerAdapter {

    private static final InternalLogger logger = InternalLoggerFactory.getInstance(ChannelInitializer.class);

    /**
     * This method will be called once the {@link Channel} was registered. After the method returns this instance
     * will be removed from the {@link ChannelPipeline} of the {@link Channel}.
     *
     * @param ch            the {@link Channel} which was registered.
     * @throws Exception    is thrown if an error occurs. In that case the {@link Channel} will be closed.
     */
    protected abstract void initChannel(C ch) throws Exception;

    @SuppressWarnings("unchecked")
    @Override
    public final void channelRegistered(ChannelHandlerContext ctx)
            throws Exception {
        boolean removed = false;
        boolean success = false;
        try {
            initChannel((C) ctx.channel());
            ctx.pipeline().remove(this);
            removed = true;
            ctx.fireChannelRegistered();
            success = true;
        } catch (Throwable t) {
            logger.warn("Failed to initialize a channel. Closing: " + ctx.channel(), t);
        } finally {
            if (!removed) {
                ctx.pipeline().remove(this);
            }
            if (!success) {
                ctx.close();
            }
        }
    }
}

所以注册之后的NioServerSocketChannel状态如下图所示：

ServerBootstrapAcceptor

private static class ServerBootstrapAcceptor extends ChannelInboundHandlerAdapter {

    private final EventLoopGroup childGroup;
    private final ChannelHandler childHandler;
    private final Entry<ChannelOption<?>, Object>[] childOptions;
    private final Entry<AttributeKey<?>, Object>[] childAttrs;

    @SuppressWarnings("unchecked")
    ServerBootstrapAcceptor(
            EventLoopGroup childGroup, ChannelHandler childHandler,
            Entry<ChannelOption<?>, Object>[] childOptions, Entry<AttributeKey<?>, Object>[] childAttrs) {
        this.childGroup = childGroup;
        this.childHandler = childHandler;
        this.childOptions = childOptions;
        this.childAttrs = childAttrs;
    }

    @Override
    @SuppressWarnings("unchecked")
    public void channelRead(ChannelHandlerContext ctx, Object msg) {
        Channel child = (Channel) msg;

        child.pipeline().addLast(childHandler);

        for (Entry<ChannelOption<?>, Object> e: childOptions) {
            try {
                if (!child.config().setOption((ChannelOption<Object>) e.getKey(), e.getValue())) {
                    logger.warn("Unknown channel option: " + e);
                }
            } catch (Throwable t) {
                logger.warn("Failed to set a channel option: " + child, t);
            }
        }

        for (Entry<AttributeKey<?>, Object> e: childAttrs) {
            child.attr((AttributeKey<Object>) e.getKey()).set(e.getValue());
        }

        try {
            childGroup.register(child);
        } catch (Throwable t) {
            child.unsafe().closeForcibly();
            logger.warn("Failed to register an accepted channel: " + child, t);
        }
    }
    // ...
}

ServerBootstrapAcceptor在channelRead事件触发的时候（也就有客户端连接的时候），把childHandler加到 childChannel Pipeline的末尾，设置childHandler的options和attrs，最后把childHandler注册进childGroup，如下 图所示：