JAVA netty 簡單使用

實現一個功能，客戶端和服務器 輪流對一個數加+1
服務器

public class Server {
	public static void main(String[] args) {
		NioEventLoopGroup boss=new NioEventLoopGroup(1);
		NioEventLoopGroup worker=new NioEventLoopGroup(3);
		try {
			final ServerBootstrap server=new ServerBootstrap();
			server.group(boss,worker).channel(NioServerSocketChannel.class)
					.childHandler(new ChannelInitializer<SocketChannel>() {
						@Override
						protected void initChannel(SocketChannel ch) throws Exception {
							ChannelPipeline pipeline = ch.pipeline();
							pipeline.addLast(new ServerHandler());
						}
					});
			ChannelFuture future = server.bind(8881).sync();
			future.channel().closeFuture().sync();
		}catch (Exception e){
			e.printStackTrace();
		}
		finally {
			boss.shutdownGracefully();
			worker.shutdownGracefully();
		}
	}
}

服務器handler

netty ChannelHandler 類似 spring mvc的filter，使用的是責任鏈模式，可以對客戶端傳來的數據進行層層解析，解碼等操作。
在沒有任何特殊操作下，默認傳遞在責任中的對象是ByteBuf

public class ServerHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {//msg 其實就是個ByteBuf 對象
        ByteBuf buf=(ByteBuf) msg;
        int i = buf.readInt();
        System.out.println("服務器收到客戶端消息"+ctx.channel().remoteAddress()+" "+i);
        ByteBuf newbuf=ctx.alloc().buffer(1024);
        newbuf.writeInt(i+1);
        ctx.writeAndFlush(newbuf);
        buf.release();
    }

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

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

客戶端

public class Client {
    public static void main(String[] args) {
        NioEventLoopGroup boss=new NioEventLoopGroup(1);
        try {
            final Bootstrap client=new Bootstrap();
            client.group(boss).channel(NioSocketChannel.class)
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ChannelPipeline pipeline = ch.pipeline();
                            pipeline.addLast(new ClientHandler());
                        }
                    });
            ChannelFuture future = client.connect("127.0.0.1",8881).sync();
            future.channel().closeFuture().sync();
        }catch (Exception e){
            e.printStackTrace();
        }
        finally {
            boss.shutdownGracefully();
        }
    }
}

客戶端handlr

public class ClientHandler extends SimpleChannelInboundHandler {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {
        ByteBuf buf=(ByteBuf)msg;
        int i=buf.readInt();
        System.out.println("客服端收到服務器"+ctx.channel().remoteAddress()+"---> "+i);
        Thread.sleep(2000);
        ByteBuf newbuf = ctx.alloc().buffer(1024);
        newbuf.writeInt(i+1);
        ctx.writeAndFlush(newbuf);
    }

    @Override
    public void channelRegistered(ChannelHandlerContext ctx) throws Exception {
        System.out.println("連接服務器成功");
    }

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

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ByteBuf buffer = ctx.alloc().buffer(1024);
        buffer.writeInt(1);
        ctx.writeAndFlush(buffer);
    }
}

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一開始很疑惑，channelRead0(ChannelHandlerContext ctx, Object msg) 方法里的msg 到底是個什么對象？ 在添加其它handler之后，比如一個StringDecode，netty會自動的把ByteBuf里的字節轉String，並傳遞在Object對象中。這是Object就是一個String。 翻了下源碼，還是很清晰的 在ChannelHandlerContext 接口中有一個fireChannelRead 方法，這個方法的解釋如下 > ChannelHandlerContext fireChannelRead(java.lang.Object msg) Description copied from interface: ChannelInboundInvoker A Channel received a message. This will result in having the ChannelInboundHandler.channelRead(ChannelHandlerContext, Object) method called of the next ChannelInboundHandler contained in the ChannelPipeline of the Channel. Specified by: fireChannelRead in interface ChannelInboundInvoker

簡單來就是會調用handler 責任鏈的下一個處理類。同過fireChannelRead方法，可以給下一個責任鏈傳遞一個對象msg，這個msg會傳遞到下一個處理類的 ChannelRead方法上。例如，StringDecode把ByteBuf轉為一個String對象msg，在調用fireChannelRead(msg),就把這個String傳到下一個handler去了。
channelRead0也是同樣的意思

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netty是基於nio的框架，要是理解了nio，其實操作起來也不是很費勁。