当前位置：首页 > news >正文

netty 学习（2）Handler的执行顺序

news 来源：原创 2024/9/21 13:33:26

摘要 Handler在netty中，无疑占据着非常重要的地位。Handler与Servlet中的filter很像，通过Handler可以完成通讯报文的解码编码、拦截指定的报文、统一对日志错误进行处理、统一对请求进行计数、控制Handler执行与否。一句话，没有它做不到的只有你想不到的。参考自：http://blog.csdn.net/u013252773/article/details/21195593

Handler在netty中，无疑占据着非常重要的地位。Handler与Servlet中的filter很像，通过Handler可以完成通讯报文的解码编码、拦截指定的报文、统一对日志错误进行处理、统一对请求进行计数、控制Handler执行与否。一句话，没有它做不到的只有你想不到的。

Netty中的所有handler都实现自ChannelHandler接口。按照输出输出来分，分为ChannelInboundHandler、ChannelOutboundHandler两大类。ChannelInboundHandler对从客户端发往服务器的报文进行处理，一般用来执行解码、读取客户端数据、进行业务处理等；ChannelOutboundHandler对从服务器发往客户端的报文进行处理，一般用来进行编码、发送报文到客户端。

Netty中，可以注册多个handler。ChannelInboundHandler按照注册的先后顺序执行；ChannelOutboundHandler按照注册的先后顺序逆序执行，如下图所示，按照注册的先后顺序对Handler进行排序，request进入Netty后的执行顺序为：

下面例子涉及的类包括：

一、HelloServer：

packagecom.yao.nettyhandler;

importio.netty.bootstrap.ServerBootstrap;

importio.netty.channel.ChannelFuture;

importio.netty.channel.ChannelInitializer;

importio.netty.channel.ChannelOption;

importio.netty.channel.EventLoopGroup;

importio.netty.channel.nio.NioEventLoopGroup;

importio.netty.channel.socket.SocketChannel;

importio.netty.channel.socket.nio.NioServerSocketChannel;

publicclass HelloServer {

publicvoid start(intport) throwsException {

EventLoopGroup bossGroup = newNioEventLoopGroup();

EventLoopGroup workerGroup = newNioEventLoopGroup();

try{

ServerBootstrap b = newServerBootstrap();

b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class)

.childHandler(newChannelInitializer<SocketChannel>() {

@Override

publicvoid initChannel(SocketChannel ch) throwsException {

// 注册两个OutboundHandler，执行顺序为注册顺序的逆序，所以应该是OutboundHandler2 OutboundHandler1

ch.pipeline().addLast(newOutboundHandler1());

ch.pipeline().addLast(newOutboundHandler2());

// 注册两个InboundHandler，执行顺序为注册顺序，所以应该是InboundHandler1 InboundHandler2

ch.pipeline().addLast(newInboundHandler1());

ch.pipeline().addLast(newInboundHandler2());

}

}).option(ChannelOption.SO_BACKLOG,128)

.childOption(ChannelOption.SO_KEEPALIVE,true);

ChannelFuture f = b.bind(port).sync();

f.channel().closeFuture().sync();

}finally{

workerGroup.shutdownGracefully();

bossGroup.shutdownGracefully();

}

publicstatic void main(String[] args) throwsException {

HelloServer server = newHelloServer();

server.start(8000);

}

二、InboundHandler1：

packagecom.yao.nettyhandler;

importio.netty.channel.ChannelHandlerContext;

importio.netty.channel.ChannelInboundHandlerAdapter;

importorg.apache.commons.logging.Log;

importorg.apache.commons.logging.LogFactory;

publicclass InboundHandler1 extendsChannelInboundHandlerAdapter {

privatestatic Log logger = LogFactory.getLog(InboundHandler1.class);

@Override

publicvoid channelRead(ChannelHandlerContext ctx, Object msg) throwsException {

logger.info("InboundHandler1.channelRead: ctx :" + ctx);

// 通知执行下一个InboundHandler

//ctx.fireChannelRead(msg);

}

@Override

publicvoid channelReadComplete(ChannelHandlerContext ctx) throwsException {

logger.info("InboundHandler1.channelReadComplete");

ctx.flush();

}

三、InboundHandler2：

packagecom.yao.nettyhandler;

importio.netty.buffer.ByteBuf;

importio.netty.channel.ChannelHandlerContext;

importio.netty.channel.ChannelInboundHandlerAdapter;

importorg.apache.commons.logging.Log;

importorg.apache.commons.logging.LogFactory;

publicclass InboundHandler2 extendsChannelInboundHandlerAdapter {

privatestatic Log logger = LogFactory.getLog(InboundHandler2.class);

@Override

// 读取Client发送的信息，并打印出来

publicvoid channelRead(ChannelHandlerContext ctx, Object msg) throwsException {

logger.info("InboundHandler2.channelRead: ctx :" + ctx);

ByteBuf result = (ByteBuf) msg;

byte[] result1 = newbyte[result.readableBytes()];

result.readBytes(result1);

String resultStr = newString(result1);

System.out.println("Client said:" + resultStr);

result.release();

ctx.write(msg);

}

@Override

publicvoid channelReadComplete(ChannelHandlerContext ctx) throwsException {

logger.info("InboundHandler2.channelReadComplete");

ctx.flush();

}

四、OutboundHandler1 ：

packagecom.yao.nettyhandler;

importio.netty.buffer.ByteBuf;

importio.netty.channel.ChannelHandlerContext;

importio.netty.channel.ChannelOutboundHandlerAdapter;

importio.netty.channel.ChannelPromise;

importorg.apache.commons.logging.Log;

importorg.apache.commons.logging.LogFactory;

publicclass OutboundHandler1 extendsChannelOutboundHandlerAdapter {

privatestatic Log logger = LogFactory.getLog(OutboundHandler1.class);

@Override

// 向client发送消息

publicvoid write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throwsException {

logger.info("OutboundHandler1.write");

String response = "I am ok!";

ByteBuf encoded = ctx.alloc().buffer(4* response.length());

encoded.writeBytes(response.getBytes());

ctx.write(encoded);

ctx.flush();

}

五、OutboundHandler2：

packagecom.yao.nettyhandler;

importio.netty.channel.ChannelHandlerContext;

importio.netty.channel.ChannelOutboundHandlerAdapter;

importio.netty.channel.ChannelPromise;

importorg.apache.commons.logging.Log;

importorg.apache.commons.logging.LogFactory;

publicclass OutboundHandler2 extendsChannelOutboundHandlerAdapter {

privatestatic Log logger = LogFactory.getLog(OutboundHandler2.class);

@Override

publicvoid write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throwsException {

logger.info("OutboundHandler2.write");

// 执行下一个OutboundHandler

super.write(ctx, msg, promise);

}

下面是客户端

六、HelloClient：

packagecom.yao.nettyhandler;

importio.netty.bootstrap.Bootstrap;

importio.netty.channel.ChannelFuture;

importio.netty.channel.ChannelInitializer;

importio.netty.channel.ChannelOption;

importio.netty.channel.EventLoopGroup;

importio.netty.channel.nio.NioEventLoopGroup;

importio.netty.channel.socket.SocketChannel;

importio.netty.channel.socket.nio.NioSocketChannel;

publicclass HelloClient {

publicvoid connect(String host, intport) throwsException {

EventLoopGroup workerGroup = newNioEventLoopGroup();

try{

Bootstrap b = newBootstrap();

b.group(workerGroup);

b.channel(NioSocketChannel.class);

b.option(ChannelOption.SO_KEEPALIVE,true);

b.handler(newChannelInitializer<SocketChannel>() {

@Override

publicvoid initChannel(SocketChannel ch) throwsException {

ch.pipeline().addLast(newHelloClientIntHandler());

}

});

// Start the client.

ChannelFuture f = b.connect(host, port).sync();

f.channel().closeFuture().sync();

}finally{

workerGroup.shutdownGracefully();

}

publicstatic void main(String[] args) throwsException {

HelloClient client = newHelloClient();

client.connect("127.0.0.1",8000);

}

七、HelloClientIntHandler：

packagecom.yao.nettyhandler;

importio.netty.buffer.ByteBuf;

importio.netty.channel.ChannelHandlerContext;

importio.netty.channel.ChannelInboundHandlerAdapter;

importorg.apache.commons.logging.Log;

importorg.apache.commons.logging.LogFactory;

publicclass HelloClientIntHandler extendsChannelInboundHandlerAdapter {

privatestatic Log logger = LogFactory.getLog(HelloClientIntHandler.class);

@Override

// 读取服务端的信息

publicvoid channelRead(ChannelHandlerContext ctx, Object msg) throwsException {

logger.info("HelloClientIntHandler.channelRead");

ByteBuf result = (ByteBuf) msg;

byte[] result1 = newbyte[result.readableBytes()];

result.readBytes(result1);

result.release();

ctx.close();

System.out.println("Server said:" + newString(result1));

}

@Override

// 当连接建立的时候向服务端发送消息，channelActive 事件当连接建立的时候会触发

publicvoid channelActive(ChannelHandlerContext ctx) throwsException {

logger.info("HelloClientIntHandler.channelActive");

String msg = "Are you ok?";

ByteBuf encoded = ctx.alloc().buffer(4* msg.length());

encoded.writeBytes(msg.getBytes());

ctx.write(encoded);

ctx.flush();

}

八、总结：

在使用Handler的过程中，需要注意：
1、ChannelInboundHandler之间的传递，通过调用 ctx.fireChannelRead(msg) 实现；调用ctx.write(msg) 将传递到ChannelOutboundHandler。
2、ctx.write()方法执行后，需要调用flush()方法才能令它立即执行。
3、ChannelOutboundHandler 在注册的时候需要放在最后一个ChannelInboundHandler之前，否则将无法传递到ChannelOutboundHandler。
4、Handler的消费处理放在最后一个处理。