Netty——BootStrap源码分析

摘要

BootStrap在netty的应用程序中负责引导服务器和客户端。netty包含了两种不同类型的引导：

• 1. 使用服务器的ServerBootStrap，用于接受客户端的连接以及为已接受的连接创建子通道。
• 2. 用于客户端的BootStrap，不接受新的连接，并且是在父通道类完成一些操作。

服务端的代码 SimpleServer.java

/**
 * Created by xjl on 2021/1/9.
 */
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

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

public class SimpleServerInitializer extends ChannelInitializer{

    @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()+"连接上");
    }
}

ServerBootstrap类分析

//使用了链式编程方式

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类的继承结构如下：

该类的参数，有必要列出：

private final Map, Object>();
private final Map, Object>();
private volatile EventLoopGroup childGroup;
private volatile ChannelHandler childHandler; 

其父类AbstractBootstrap的参数

private volatile EventLoopGroup group;
private volatile ChannelFactory, Object> options = new LinkedHashMap, Object> attrs = new LinkedHashMap, Object> options = new LinkedHashMap