netty 学习 Handler的执行顺序
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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:
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package com.yao.nettyhandler; ?
import io.netty.bootstrap.ServerBootstrap; import io.netty.channel.ChannelFuture; import io.netty.channel.ChannelInitializer; import io.netty.channel.ChannelOption; import io.netty.channel.EventLoopGroup; import io.netty.channel.nio.NioEventLoopGroup; import io.netty.channel.socket.SocketChannel; import io.netty.channel.socket.nio.NioServerSocketChannel; ?
public class HelloServer { ???? public void start( int port) throws Exception { ???????? EventLoopGroup bossGroup = new NioEventLoopGroup(); ???????? EventLoopGroup workerGroup = new NioEventLoopGroup(); ???????? try { ???????????? ServerBootstrap b = new ServerBootstrap(); ???????????? b.group(bossGroup, workerGroup).channel(NioServerSocketChannel. class ) ???????????????????? .childHandler( new ChannelInitializer ???????????????????????????????? @Override ???????????????????????????????? public void initChannel(SocketChannel ch) throws Exception { ???????????????????????????????????? // 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( new OutboundHandler1()); ???????????????????????????????????? ch.pipeline().addLast( new OutboundHandler2()); ???????????????????????????????????? // 注册两个InboundHandler,执行顺序为注册顺序,所以应该是InboundHandler1 InboundHandler2 ???????????????????????????????????? ch.pipeline().addLast( new InboundHandler1()); ???????????????????????????????????? ch.pipeline().addLast( new InboundHandler2()); ???????????????????????????????? } ???????????????????????????? }).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(); ???????? } ???? } ?
???? public static void main(String[] args) throws Exception { ???????? HelloServer server = new HelloServer(); ???????? server.start( 8000 ); ???? } } |
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package com.yao.nettyhandler; ?
import io.netty.channel.ChannelHandlerContext; import io.netty.channel.ChannelInboundHandlerAdapter; ?
import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; ?
public class InboundHandler1 extends ChannelInboundHandlerAdapter { ???? private static Log logger = LogFactory.getLog(InboundHandler1. class ); ?
???? @Override ???? public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { ???????? logger.info( "InboundHandler1.channelRead: ctx :" + ctx); ???????? ????????? // 通知执行下一个InboundHandler ???????? //ctx.fireChannelRead(msg); ???? } ?
???? @Override ???? public void channelReadComplete(ChannelHandlerContext ctx) throws Exception { ???????? logger.info( "InboundHandler1.channelReadComplete" ); ???????? ctx.flush(); ???? } } |
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package com.yao.nettyhandler; ?
import io.netty.buffer.ByteBuf; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.ChannelInboundHandlerAdapter; ?
import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; ?
public class InboundHandler2 extends ChannelInboundHandlerAdapter { ???? private static Log? logger? = LogFactory.getLog(InboundHandler2. class ); ?
???? @Override ???? // 读取Client发送的信息,并打印出来 ???? public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { ???????? logger.info( "InboundHandler2.channelRead: ctx :" + ctx); ???????? ByteBuf result = (ByteBuf) msg; ???????? byte [] result1 = new byte [result.readableBytes()]; ???????? result.readBytes(result1); ???????? String resultStr = new String(result1); ???????? System.out.println( "Client said:" + resultStr); ???????? result.release(); ?
???????? ctx.write(msg); ???? } ?
???? @Override ???? public void channelReadComplete(ChannelHandlerContext ctx) throws Exception { ???????? logger.info( "InboundHandler2.channelReadComplete" ); ???????? ctx.flush(); ???? } ?
} |
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package com.yao.nettyhandler; ?
import io.netty.buffer.ByteBuf; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.ChannelOutboundHandlerAdapter; import io.netty.channel.ChannelPromise; ?
import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; ?
public class OutboundHandler1 extends ChannelOutboundHandlerAdapter { ???? private static Log? logger? = LogFactory.getLog(OutboundHandler1. class ); ???? @Override ???? // 向client发送消息 ???? public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception { ???????? 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:
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package com.yao.nettyhandler; ?
import io.netty.channel.ChannelHandlerContext; import io.netty.channel.ChannelOutboundHandlerAdapter; import io.netty.channel.ChannelPromise; ?
import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; ?
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public class OutboundHandler2 extends ChannelOutboundHandlerAdapter { ???? private static Log? logger? = LogFactory.getLog(OutboundHandler2. class ); ???? ????? @Override ???? public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception { ???????? logger.info( "OutboundHandler2.write" ); ???????? // 执行下一个OutboundHandler ???????? super .write(ctx, msg, promise); ???? } } |
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下面是客户端?
六、HelloClient:
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package com.yao.nettyhandler; ?
import io.netty.bootstrap.Bootstrap; import io.netty.channel.ChannelFuture; import io.netty.channel.ChannelInitializer; import io.netty.channel.ChannelOption; import io.netty.channel.EventLoopGroup; import io.netty.channel.nio.NioEventLoopGroup; import io.netty.channel.socket.SocketChannel; import io.netty.channel.socket.nio.NioSocketChannel; ?
public class HelloClient { ???? public void connect(String host, int port) throws Exception { ???????? EventLoopGroup workerGroup = new NioEventLoopGroup(); ?
???????? try { ???????????? Bootstrap b = new Bootstrap(); ???????????? b.group(workerGroup); ???????????? b.channel(NioSocketChannel. class ); ???????????? b.option(ChannelOption.SO_KEEPALIVE, true ); ???????????? b.handler( new ChannelInitializer ???????????????? @Override ???????????????? public void initChannel(SocketChannel ch) throws Exception { ???????????????????? ch.pipeline().addLast( new HelloClientIntHandler()); ???????????????? } ???????????? }); ?
???????????? // Start the client. ???????????? ChannelFuture f = b.connect(host, port).sync(); ???????????? f.channel().closeFuture().sync(); ???????? } finally { ???????????? workerGroup.shutdownGracefully(); ???????? } ???? } ?
???? public static void main(String[] args) throws Exception { ???????? HelloClient client = new HelloClient(); ???????? client.connect( "127.0.0.1" , 8000 ); ???? } } |
七、HelloClientIntHandler:
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package com.yao.nettyhandler; ?
import io.netty.buffer.ByteBuf; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.ChannelInboundHandlerAdapter; ?
import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; ?
public class HelloClientIntHandler extends ChannelInboundHandlerAdapter { ???? private static Log? logger? = LogFactory.getLog(HelloClientIntHandler. class ); ???? @Override ???? // 读取服务端的信息 ???? public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { ???????? logger.info( "HelloClientIntHandler.channelRead" ); ???????? ByteBuf result = (ByteBuf) msg; ???????? byte [] result1 = new byte [result.readableBytes()]; ???????? result.readBytes(result1); ???????? result.release(); ???????? ctx.close(); ???????? System.out.println( "Server said:" + new String(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 ???? public void channelActive(ChannelHandlerContext ctx) throws Exception { ???????? 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(); ???? } } |
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。