第 8 章 引导

1. 引导类的层次结构包括一个抽象的父类和两个具体的引导子类，服务器致力于使用一个父 Channel 来接受来自客户端的连接，并创建子 Channel 以用于它们之间的通信；而客户端将最可能只需要一个单独的、没有父 Channel 的 Channel 来用于所有的网络交互;Cloneable便于创建相同配置的引导类的浅拷贝

   
   
   

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2. 子类型 B 是其父类型的一个类型参数，可以返回运行时的实例的引用以支持方法的链式调用
   public abstract class AbstractBootstrap ,C extends Channel>
3. ServerBootstrap可分别设置ServerChannel和子Channel的option和attr，而Bootstrap则只创建一个Channel
   
   

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4. 可以从Channel引导客户端，简单的例子就是在服务端连接建立后，再作为客户端去连接其他服务（如数据库等）
   
   

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   public class BootstrapSharingEventLoopGroup {
           public void bootstrap() {
               ServerBootstrap bootstrap = new ServerBootstrap();
               bootstrap.group(new NioEventLoopGroup(), new NioEventLoopGroup())
                   .channel(NioServerSocketChannel.class)
                   .childHandler(
                       new SimpleChannelInboundHandler() {
                           ChannelFuture connectFuture;
                           @Override
                           public void channelActive(ChannelHandlerContext ctx)
                               throws Exception {
                               // 作为客户端连接其他服务
                               Bootstrap bootstrap = new Bootstrap();
                               bootstrap.channel(NioSocketChannel.class).handler(
                                   new SimpleChannelInboundHandler() {
                                       @Override
                                       protected void channelRead0(
                                           ChannelHandlerContext ctx, ByteBuf in)
                                           throws Exception {
                                           System.out.println("Received data");
                                       }
                                   });
                               // 复用 EventLoop
                               bootstrap.group(ctx.channel().eventLoop());
                               connectFuture = bootstrap.connect(
                                   new InetSocketAddress("www.manning.com", 80));
                           }
       
                           @Override
                           protected void channelRead0(
                               ChannelHandlerContext channelHandlerContext,
                                   ByteBuf byteBuf) throws Exception {
                               if (connectFuture.isDone()) {
                                   // do something with the data
                               }
                           }
                       });
               ChannelFuture future = bootstrap.bind(new InetSocketAddress(8080));
               future.addListener(new ChannelFutureListener() {
                   @Override
                   public void operationComplete(ChannelFuture channelFuture)
                       throws Exception {
                       if (channelFuture.isSuccess()) {
                           System.out.println("Server bound");
                       } else {
                           System.err.println("Bind attempt failed");
                           channelFuture.cause().printStackTrace();
                       }
                   }
               });
           }
       }
   

5. 抽象类ChannelInboundHandlerAdapter定义了initChannel方法，可将多个ChannelHandler添加到一个ChannelPipeline中的简便方法，ChannelInitializer为其子类，只需重写该方法即可，一旦Channel被注册到了它的EventLoop之后，就会调用initChannel

   public class BootstrapWithInitializer {
       public void bootstrap() throws InterruptedException {
           ServerBootstrap bootstrap = new ServerBootstrap();
           bootstrap.group(new NioEventLoopGroup(), new NioEventLoopGroup())
               .channel(NioServerSocketChannel.class)
               .childHandler(new ChannelInitializerImpl());
           ChannelFuture future = bootstrap.bind(new InetSocketAddress(8080));
           future.sync();
       }
   
       final class ChannelInitializerImpl extends ChannelInitializer {
           @Override
           protected void initChannel(Channel ch) throws Exception {
               ChannelPipeline pipeline = ch.pipeline();
               pipeline.addLast(new HttpClientCodec());
               pipeline.addLast(new HttpObjectAggregator(Integer.MAX_VALUE));
   
           }
       }
   }
   

6. ChannelOption和AttributeKey将在connect或者bind方法被调用时设置到已创建的Channel上，可在事件处理方法中使用

   public class BootstrapClientWithOptionsAndAttrs {
       public void bootstrap() {
           final AttributeKey id = AttributeKey.newInstance("ID");
           Bootstrap bootstrap = new Bootstrap();
           bootstrap.group(new NioEventLoopGroup())
               .channel(NioSocketChannel.class)
               .handler(
                   new SimpleChannelInboundHandler() {
                       @Override
                       public void channelRegistered(ChannelHandlerContext ctx)
                           throws Exception {
                           Integer idValue = ctx.channel().attr(id).get();
                           // do something with the idValue
                       }
   
                       @Override
                       protected void channelRead0(
                           ChannelHandlerContext channelHandlerContext,
                           ByteBuf byteBuf) throws Exception {
                           System.out.println("Received data");
                       }
                   }
               );
           bootstrap.option(ChannelOption.SO_KEEPALIVE, true)
               .option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 5000);
           bootstrap.attr(id, 123456);
           ChannelFuture future = bootstrap.connect(
               new InetSocketAddress("www.manning.com", 80));
           future.syncUninterruptibly();
       }
   }
   

7. Bootstrap也可用于无连接的协议，Netty 提供了各种DatagramChannel的实现，唯一区别就是不再调用connect，而只调用bind

   public class BootstrapDatagramChannel {
       public void bootstrap() {
           Bootstrap bootstrap = new Bootstrap();
           bootstrap.group(new OioEventLoopGroup()).channel(
               OioDatagramChannel.class).handler(
               new SimpleChannelInboundHandler() {
                   @Override
                   public void channelRead0(ChannelHandlerContext ctx,
                       DatagramPacket msg) throws Exception {
                       // Do something with the packet
                   }
               }
           );
           ChannelFuture future = bootstrap.bind(new InetSocketAddress(0));
           future.addListener(new ChannelFutureListener() {
               @Override
               public void operationComplete(ChannelFuture channelFuture)
                  throws Exception {
                  if (channelFuture.isSuccess()) {
                      System.out.println("Channel bound");
                  } else {
                      System.err.println("Bind attempt failed");
                      channelFuture.cause().printStackTrace();
                  }
               }
           });
       }
   }
   

8. EventLoopGroup.shutdownGracefully()会优雅的关闭Netty应用，关闭EventLoopGroup，处理任何挂起的事件和任务，随后释放所有活动的线程，返回一个Future，在关闭完成时接收通知

   public class GracefulShutdown {
       public static void main(String args[]) {
           GracefulShutdown client = new GracefulShutdown();
           client.bootstrap();
       }
       public void bootstrap() {
           EventLoopGroup group = new NioEventLoopGroup();
           Bootstrap bootstrap = new Bootstrap();
           bootstrap.group(group)
                .channel(NioSocketChannel.class)
                .handler(
                   new SimpleChannelInboundHandler() {
                       @Override
                       protected void channelRead0(
                               ChannelHandlerContext channelHandlerContext,
                               ByteBuf byteBuf) throws Exception {
                           System.out.println("Received data");
                       }
                   }
                );
           bootstrap.connect(new InetSocketAddress("www.manning.com", 80)).syncUninterruptibly();      
           Future future = group.shutdownGracefully();
           // block until the group has shutdown
           future.syncUninterruptibly();
       }
   }