Handler链调用机制实例

• 使用自定义的编码器和解码器来说明Netty的handler 调用机制，客户端发送long 到服务器

• MyServer

public class MyServer {
    public static void main(String[] args) throws Exception{

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

        try {
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(bossGroup,workerGroup).channel(
                    NioServerSocketChannel.class).childHandler(new MyServerInitializer()); //自定义一个初始化类

            ChannelFuture channelFuture = serverBootstrap.bind(7000).sync();
            channelFuture.channel().closeFuture().sync();

        }finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }

    }
}

• MyServerInitializer

public class MyServerInitializer extends ChannelInitializer<SocketChannel> {

    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();//一会下断点

        //入站的handler进行解码 MyByteToLongDecoder
        pipeline.addLast(new MyByteToLongDecoder());
        
        //自定义的handler 处理业务逻辑
        pipeline.addLast(new MyServerHandler());
    }
}

• MyByteToLongDecoder

public class MyByteToLongDecoder extends ByteToMessageDecoder {
    /**
     *
     * decode 会根据接收的数据，被调用多次, 直到确定没有新的元素被添加到list
     * , 或者是ByteBuf 没有更多的可读字节为止
     * 如果list out 不为空，就会将list的内容传递给下一个 channelinboundhandler处理, 该处理器的方法也会被调用多次
     *
     * @param ctx 上下文对象
     * @param in 入站的 ByteBuf
     * @param out List 集合，将解码后的数据传给下一个handler
     * @throws Exception
     */
    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {

        System.out.println("MyByteToLongDecoder 被调用");
        //因为 long 8个字节, 需要判断有8个字节，才能读取一个long
        if(in.readableBytes() >= 8) {
            out.add(in.readLong());
        }
    }
}

• MyServerHandler

public class MyServerHandler extends SimpleChannelInboundHandler<Long> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, Long msg) throws Exception {

        System.out.println("从客户端" + ctx.channel().remoteAddress() + " 读取到long " + msg);
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
}

• MyClient

public class MyClient {
    public static void main(String[] args)  throws  Exception{

        EventLoopGroup group = new NioEventLoopGroup();

        try {

            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(group).channel(NioSocketChannel.class)
                    .handler(new MyClientInitializer()); //自定义一个初始化类

            ChannelFuture channelFuture =
                    bootstrap.connect("localhost", 7000).sync();

            channelFuture.channel().closeFuture().sync();

        }finally {
            group.shutdownGracefully();
        }
    }
}

• MyClientInitializer

public class MyClientInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {

        ChannelPipeline pipeline = ch.pipeline();

        //加入一个出站的handler 对数据进行一个编码
        pipeline.addLast(new MyLongToByteEncoder());

        //加入一个自定义的handler，处理业务
        pipeline.addLast(new MyClientHandler());
    }
}

• MyLongToByteEncoder

public class MyLongToByteEncoder extends MessageToByteEncoder<Long> {
    //编码方法
    @Override
    protected void encode(ChannelHandlerContext ctx, Long msg, ByteBuf out) throws Exception {

        System.out.println("MyLongToByteEncoder encode 被调用");
        System.out.println("msg=" + msg);
        out.writeLong(msg);

    }
}

• MyClientHandler

public class MyClientHandler  extends SimpleChannelInboundHandler<Long> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, Long msg) throws Exception {

        System.out.println("服务器的ip=" + ctx.channel().remoteAddress());
        System.out.println("收到服务器消息=" + msg);
    }

    //重写channelActive 发送数据
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("MyClientHandler 发送数据");
        //ctx.writeAndFlush(Unpooled.copiedBuffer(""))
        ctx.writeAndFlush(123456L); //发送的是一个long
    }
}

• 先启动服务端，再启动客户端

# 服务端控制台
MyByteToLongDecoder 被调用
从客户端/127.0.0.1:53008 读取到long 123456

# 客户端控制台
MyClientHandler 发送数据
MyLongToByteEncoder encode 被调用
msg=123456

• 服务端发送long 到客户端
  

• MyServerHandler中添加如下

//给客户端发送一个long
ctx.writeAndFlush(98765L);

• MyServerInitializer中添加如下

//出站的handler进行编码
pipeline.addLast(new MyLongToByteEncoder());

• MyClientInitializer中添加如下

//这时一个入站的解码器(入站handler )
pipeline.addLast(new MyByteToLongDecoder());

• 先启动服务端，再启动客户端测试

# 服务端控制台
MyByteToLongDecoder 被调用
从客户端/127.0.0.1:62913 读取到long 123456
MyLongToByteEncoder encode 被调用
msg=98765

# 客户端控制台
MyClientHandler 发送数据
MyLongToByteEncoder encode 被调用
msg=123456
MyByteToLongDecoder 被调用
服务器的ip=localhost/127.0.0.1:7000
收到服务器消息=98765

• 不论解码器handler 还是 编码器handler 即接收的消息类型必须与待处理的消息类型一致，否则该handler不会被执行
• 在解码器 进行数据解码时，需要判断 缓存区(ByteBuf)的数据是否足够 ，否则接收到的结果会期望结果可能不一致