Android 基于Netty的消息推送方案之字符串的接收和发送（三）

在上一篇文章中《Android 基于Netty的消息推送方案之概念和工作原理(二)》 ，我们介绍过一些关于Netty的概念和工作原理的内容，今天我们先来介绍一个叫做ChannelBuffer的东东。

ChannelBuffer

 Netty中的消息传递，都必须以字节的形式，以ChannelBuffer为载体传递。简单的说，就是你想直接写个字符串过去，对不起，抛异常。虽然，Netty定义的writer的接口参数是Object的，这可能也是会给新上手的朋友容易造成误会的地方。Netty源码中，是这样判断的。

SendBuffer acquire(Object message) {
        if (message instanceof ChannelBuffer) {
            return acquire((ChannelBuffer) message);
        } else if (message instanceof FileRegion) {
            return acquire((FileRegion) message);
        }

        throw new IllegalArgumentException(
                "unsupported message type: " + message.getClass());
    }

接下来我们写一个Demo来学习它。

服务端代码如下

public class MessageServer {
    public static void main(String args[]){
        //服务启动器
        ServerBootstrap bootstrap = new ServerBootstrap(new NioServerSocketChannelFactory(Executors.newCachedThreadPool(),Executors.newCachedThreadPool()));
        //设置一个处理客户端消息和各种消息事件的类(Handler)
        bootstrap.setPipelineFactory(new ChannelPipelineFactory(){
            @Override
            public ChannelPipeline getPipeline() throws Exception {
                return Channels.pipeline(new BusinessHandler());
            }
        });
        //开放8000端口供客户端连接
        bootstrap.bind(new InetSocketAddress(8000));
    }

    private static class BusinessHandler extends SimpleChannelHandler{
        // 服务端收到客户端发送过来的消息时，触发此方法
        @Override
        public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) throws Exception {
            ChannelBuffer buffer = (ChannelBuffer)e.getMessage();
            System.out.println("Receive:"+buffer.toString(Charset.defaultCharset()));
            String msg = buffer.toString(Charset.defaultCharset()) + "has been processed!";
            ChannelBuffer buffer2 = ChannelBuffers.buffer(msg.length());
            buffer2.writeBytes(msg.getBytes());
            e.getChannel().write(buffer2);
        }
    }
}

客户端代码如下

public class MessageClient {
    public static void main(String args[]) {
        ClientBootstrap bootstrap = new ClientBootstrap(new NioClientSocketChannelFactory(Executors.newCachedThreadPool(), Executors.newCachedThreadPool()));

        bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
            @Override
            public ChannelPipeline getPipeline() throws Exception {
                return Channels.pipeline(new MessageClientHandler());
            }
        });
        bootstrap.connect(new InetSocketAddress("127.0.0.1", 8000));
    }

    private static class MessageClientHandler extends SimpleChannelHandler {
        /**
         * 当绑定到服务端的时候触发，给服务端发消息。
         */
        @Override
        public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e) {
            // 将字符串，构造成ChannelBuffer，传递给服务端
            String msg = "Hello, I'm client.";
            ChannelBuffer buffer = ChannelBuffers.buffer(msg.length());
            buffer.writeBytes(msg.getBytes());
            e.getChannel().write(buffer);
        }
    }
}

先启动服务端，再启动客户端，可以看到服务端打印如下字符串

Receive:Hello, I'm client.

如果你感兴趣，请继续阅读《Android 基于Netty的消息推送方案之对象的传递（四）》