在学习Netty编程之前,我们先了解一下为什么要使用Netty, 通过前几篇的代码,大家发现JDK的NIO API太不好用了。JDK自带的API主要有一下4个贴点:
1) NIO的类库和API繁杂,使用麻烦,你需要熟练掌握Selector、ServerSocketChannel、SocketChannel、ByteBuffer等;
2) 需要具备其它的额外技能做铺垫,例如熟悉Java多线程编程,因为NIO编程涉及到Reactor模式,你必须对多线程和网路编程非常熟悉,才能编写出高质量的NIO程序;
3) 可靠性能力补齐,工作量和难度都非常大。例如客户端面临断连重连、网络闪断、半包读写、失败缓存、网络拥塞和异常码流的处理等等,NIO编程的特点是功能开发相对容易,但是可靠性能力补齐工作量和难度都非常大;
4) JDK NIO的BUG,例如臭名昭著的epoll bug,它会导致Selector空轮询,最终导致CPU 100%。官方声称在JDK1.6版本的update18修复了该问题,但是直到JDK1.7版本该问题仍旧存在,只不过该bug发生概率降低了一些而已,它并没有被根本解决。该BUG以及与该BUG相关的问题单如下:
那Netty的主要好处就是以下几点:
1) API使用简单,开发门槛低;
2) 功能强大,预置了多种编解码功能,支持多种主流协议;
3) 定制能力强,可以通过ChannelHandler对通信框架进行灵活的扩展;
4) 性能高,通过与其它业界主流的NIO框架对比,Netty的综合性能最优;
5) 成熟、稳定,Netty修复了已经发现的所有JDK NIO BUG,业务开发人员不需要再为NIO的BUG而烦恼;
6) 社区活跃,版本迭代周期短,发现的BUG可以被及时修复,同时,更多的新功能会被加入;
7) 经历了大规模的商业应用考验,质量已经得到验证。在互联网、大数据、网络游戏、企业应用、电信软件等众多行业得到成功商用,证明了它可以完全满足不同行业的商业应用。
下面就让代码说明一切吧:
TimeServer 端主要有两个类完成,Server启动类 和消息处理的Handler
package com.techstar.netty; 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 NettyTimeServer { public void bind(int port) { EventLoopGroup bossGroup = new NioEventLoopGroup(); EventLoopGroup workerGroup = new NioEventLoopGroup(); try { ServerBootstrap bootstrap = new ServerBootstrap(); bootstrap.group(bossGroup, workerGroup) .channel(NioServerSocketChannel.class) .option(ChannelOption.SO_BACKLOG, 1024) .childHandler(new ChildChannelHandler()); ChannelFuture syncFuture = bootstrap.bind(port).sync(); System.out.println("time server listener started!"); syncFuture.channel().closeFuture().sync(); } catch (InterruptedException e) { e.printStackTrace(); } finally { bossGroup.shutdownGracefully(); workerGroup.shutdownGracefully(); } } private class ChildChannelHandler extends ChannelInitializer<SocketChannel> { @Override protected void initChannel(SocketChannel channel) throws Exception { channel.pipeline().addLast(new NettyTimeServerHandler()); } } /** * 主函数,启动服务器 * @param args */ public static void main(String[] args) { System.out.println("time server starting.........."); new NettyTimeServer().bind(8081); System.out.println("time server started.........."); } }
package com.techstar.netty; import java.util.Date; import io.netty.buffer.ByteBuf; import io.netty.buffer.Unpooled; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.SimpleChannelInboundHandler; /** * handler * @author mrh * */ public class NettyTimeServerHandler extends SimpleChannelInboundHandler<ByteBuf> { @Override protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception { // TODO Auto-generated method stub byte[] req = new byte[msg.readableBytes()]; msg.readBytes(req); String body = new String(req, "UTF-8"); System.out.println("The time server receive order : " + body); String currentTime = "QUERY TIME ORDER".equals(body)?new Date(System.currentTimeMillis()).toString() : "BAD ORDER"; ByteBuf response = Unpooled.copiedBuffer(currentTime.getBytes()); ctx.write(response); } @Override public void channelReadComplete(ChannelHandlerContext ctx) throws Exception { // TODO Auto-generated method stub ctx.flush(); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { ctx.close(); } }
TimeClient 也是两个类完成, Client启动类和消息处理的Handler
package com.techstar.netty; 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 NettyTimeClient { public void connect (String host, int port) { EventLoopGroup group = new NioEventLoopGroup(); try { Bootstrap bootstrap = new Bootstrap(); bootstrap.group(group).channel(NioSocketChannel.class) .option(ChannelOption.TCP_NODELAY, true) .handler(new ChannelInitializer<SocketChannel>() { @Override protected void initChannel(SocketChannel ch) throws Exception { ch.pipeline().addLast(new NettyTimeClientHandler()); } }); ChannelFuture future = bootstrap.connect(host, port).sync(); future.channel().closeFuture().sync(); } catch (Exception e) { e.printStackTrace(); } finally { group.shutdownGracefully(); } } public static void main(String[] args) { new NettyTimeClient().connect("127.0.0.1", 8081); } }
package com.techstar.netty; import io.netty.buffer.ByteBuf; import io.netty.buffer.Unpooled; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.SimpleChannelInboundHandler; public class NettyTimeClientHandler extends SimpleChannelInboundHandler<ByteBuf>{ private final ByteBuf firstMessage; public NettyTimeClientHandler() { byte[] request = "QUERY TIME ORDER".getBytes(); this.firstMessage = Unpooled.buffer(request.length); this.firstMessage.writeBytes(request); } @Override public void channelActive(ChannelHandlerContext ctx) throws Exception { ctx.writeAndFlush(firstMessage); } @Override protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) throws Exception { byte[] request = new byte[msg.readableBytes()]; msg.readBytes(request); String body = new String(request, "UTF-8"); System.out.println(body); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception { // TODO Auto-generated method stub cause.printStackTrace(); ctx.close(); } }