JAVA通信系列三：Netty入门总结（转）

一、Netty学习资料

书籍《Netty In Action中文版》

对于Netty的十一个疑问
http://news.cnblogs.com/n/205413/

深入浅出Netty
http://wenku.baidu.com/view/7765bc2db4daa58da0114a4c.html

Netty了解与小试 
http://www.cnblogs.com/xd502djj/archive/2012/06/25/2561318.html

Netty系列之Netty高性能之道【精彩】
http://www.infoq.com/cn/articles/netty-high-performance/

Netty系列之Netty 服务端创建【精彩】
http://www.infoq.com/cn/articles/netty-server-create

Netty 5用户指南
http://ifeve.com/netty5-user-guide/

基于Netty5.0入门案例六之NettyServer群发消息
http://www.bubuko.com/infodetail-575271.html

Netty5入门学习笔记002-TCP粘包/拆包问题的解决之道（上）
http://my.oschina.net/imhoodoo/blog/357290

基于Netty与RabbitMQ的消息服务 
http://www.cnblogs.com/luxiaoxun/archive/2015/01/28/4257105.html

基于Netty5.0入门案例五之NettyServer字符串编码器
http://www.itstack.org/?post=9

二、代码示例

Hello world
1.编写处理器 DiscardServerHandler extends ChannelHandlerAdapter
2.编写Main方法，启动DiscardServerHandler

Echo
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) {
    ByteBuf in = (ByteBuf) msg;
    try {
        while (in.isReadable()) { // (1)
            System.out.print((char) in.readByte());
            System.out.flush();
        }
    } finally {
        ReferenceCountUtil.release(msg); // (2)
    }
}

Time
@Override
    public void channelActive(final ChannelHandlerContext ctx) { // (1)
        final ByteBuf time = ctx.alloc().buffer(4); // (2)
        time.writeInt((int) (System.currentTimeMillis() / 1000L + 2208988800L));

        final ChannelFuture f = ctx.writeAndFlush(time); // (3)
        f.addListener(new ChannelFutureListener() {
            @Override
            public void operationComplete(ChannelFuture future) {
                assert f == future;
                ctx.close();
            }
        }); // (4)
    }

流数据的传输处理【分包，黏包】
1.ChannelHandler有2个生命周期的监听方法：handlerAdded()和handlerRemoved()。你可以完成任意初始化任务只要他不会被阻塞很长的时间。
public class TimeClientHandler extends ChannelHandlerAdapter {
    private ByteBuf buf;

    @Override
    public void handlerAdded(ChannelHandlerContext ctx) {
        buf = ctx.alloc().buffer(4); // (1)
    }

    @Override
    public void handlerRemoved(ChannelHandlerContext ctx) {
        buf.release(); // (1)
        buf = null;
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) {
        ByteBuf m = (ByteBuf) msg;
        buf.writeBytes(m); // (2)
        m.release();

        if (buf.readableBytes() >= 4) { // (3)
            long currentTimeMillis = (buf.readInt() - 2208988800L) * 1000L;
            System.out.println(new Date(currentTimeMillis));
            ctx.close();
        }
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
        cause.printStackTrace();
        ctx.close();
    }
}
2.TimeClientHandler拆分成2个处理器：TimeDecoder处理数据拆分的问题，TimeClientHandler原始版本的实现

public class TimeDecoder extends ByteToMessageDecoder { // (1)
    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) { // (2)
        if (in.readableBytes() < 4) {
            return; // (3)
        }

        out.add(in.readBytes(4)); // (4)
    }
}

用POJO代替ByteBuf