Netty介绍
按照定义来说,Netty是一个异步、事件驱动的用来做高性能、高可靠性的网络应用框架。主要的优点有:
- 框架设计优雅,底层模型随意切换适应不同的网络协议要求
- 提供很多标准的协议、安全、编码解码的支持
- 解决了很多NIO不易用的问题
- 社区更为活跃,在很多开源框架中使用,如Dubbo、RocketMQ、Spark等
主要支持的功能或者特性有:
image
- 底层核心有:Zero-Copy-Capable Buffer,非常易用的灵拷贝Buffer(这个内容很有意思,稍后专门来说);统一的API;标准可扩展的时间模型
- 传输方面的支持有:管道通信(具体不知道干啥的,还请老司机指教);Http隧道;TCP与UDP
- 协议方面的支持有:基于原始文本和二进制的协议;解压缩;大文件传输;流媒体传输;protobuf编解码;安全认证;http和websocket
总之提供了很多现成的功能可以直接供开发者使用。
Netty服务器小例子
基于Netty的服务器编程可以看做是Reactor模型:
image
即包含一个接收连接的线程池(也有可能是单个线程,boss线程池)以及一个处理连接的线程池(worker线程池)。boss负责接收连接,并进行IO监听;worker负责后续的处理。为了便于理解Netty,直接看看代码:
package cn.xingoo.book.netty.chap04;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import java.net.InetSocketAddress;
import java.nio.charset.Charset;
public class NettyNioServer {
public void serve(int port) throws InterruptedException {
final ByteBuf buffer = Unpooled.unreleasableBuffer(Unpooled.copiedBuffer("Hi\r\n", Charset.forName("UTF-8")));
// 第一步,创建线程池
EventLoopGroup bossGroup = new NioEventLoopGroup(1);
EventLoopGroup workerGroup = new NioEventLoopGroup();
try{
// 第二步,创建启动类
ServerBootstrap b = new ServerBootstrap();
// 第三步,配置各组件
b.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class)
.localAddress(new InetSocketAddress(port))
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel socketChannel) throws Exception {
socketChannel.pipeline().addLast(new ChannelInboundHandlerAdapter(){
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
ctx.writeAndFlush(buffer.duplicate()).addListener(ChannelFutureListener.CLOSE);
}
});
}
});
// 第四步,开启监听
ChannelFuture f = b.bind().sync();
f.channel().closeFuture().sync();
} finally {
bossGroup.shutdownGracefully().sync();
workerGroup.shutdownGracefully().sync();
}
}
public static void main(String[] args) throws InterruptedException {
NettyNioServer server = new NettyNioServer();
server.serve(5555);
}
}
代码非常少,而且想要换成阻塞IO,只需要替换Channel里面的工厂类即可:
public class NettyOioServer {
public void serve(int port) throws InterruptedException {
final ByteBuf buf = Unpooled.unreleasableBuffer(Unpooled.copiedBuffer("Hi\r\b", Charset.forName("UTF-8")));
EventLoopGroup bossGroup = new OioEventLoopGroup(1);
EventLoopGroup workerGroup = new OioEventLoopGroup();
try{
ServerBootstrap b = new ServerBootstrap();
b.group(bossGroup, workerGroup)//配置boss和worker
.channel(OioServerSocketChannel.class) // 使用阻塞的SocketChannel
....
概括来说,在Netty中包含下面几个主要的组件:
- Bootstrap:netty的组件容器,用于把其他各个部分连接起来;如果是TCP的Server端,则为ServerBootstrap.
- Channel:代表一个Socket的连接
- EventLoopGroup:一个Group包含多个EventLoop,可以理解为线程池
- EventLoop:处理具体的Channel,一个EventLoop可以处理多个Channel
- ChannelPipeline:每个Channel绑定一个pipeline,在上面注册处理逻辑handler
- Handler:具体的对消息或连接的处理,有两种类型,Inbound和Outbound。分别代表消息接收的处理和消息发送的处理。
- ChannelFuture:注解回调方法
了解上面的基本组件后,就看一下几个重要的内容。
Netty的Buffer和零拷贝
在Unix操作系统中,系统底层可以基于mmap实现内核空间和用户空间的内存映射。但是在Netty中并不是这个意思,它主要来自于下面几个功能:
image- 通过Composite和slice实现逻辑上的Buffer的组合和拆分,重新维护索引,避免内存拷贝过程。
- 通过DirectBuffer申请堆外内存,避免用户空间的拷贝。不过堆外内存的申请和释放都很麻烦,推荐小心使用。关于堆外内存的一些研究,还可以参考执勤的分享:Java堆外内存之突破JVM枷锁 以及 Java直接内存与非直接内存性能测试
- 通过FileRegion包装FileChannel,直接实现channel到channel的传输。
另外,Netty自己封装实现了ByteBuf,相比于Nio原生的ByteBuffer,API上更易用了;同时支持容量的动态扩容;另外还支持Buffer的池化,高效复用Buffer。
public class ByteBufTest {
public static void main(String[] args) {
//创建bytebuf
ByteBuf buf = Unpooled.copiedBuffer("hello".getBytes());
System.out.println(buf);
// 读取一个字节
buf.readByte();
System.out.println(buf);
// 读取一个字节
buf.readByte();
System.out.println(buf);
// 丢弃无用数据
buf.discardReadBytes();
System.out.println(buf);
// 清空
buf.clear();
System.out.println(buf);
// 写入
buf.writeBytes("123".getBytes());
System.out.println(buf);
buf.markReaderIndex();
System.out.println("mark:"+buf);
buf.readByte();
buf.readByte();
System.out.println("read:"+buf);
buf.resetReaderIndex();
System.out.println("reset:"+buf);
}
}
输出为:
UnpooledHeapByteBuf(ridx: 0, widx: 5, cap: 5/5)
UnpooledHeapByteBuf(ridx: 1, widx: 5, cap: 5/5)
UnpooledHeapByteBuf(ridx: 2, widx: 5, cap: 5/5)
UnpooledHeapByteBuf(ridx: 0, widx: 3, cap: 5/5)
UnpooledHeapByteBuf(ridx: 0, widx: 0, cap: 5/5)
UnpooledHeapByteBuf(ridx: 0, widx: 3, cap: 5/5)
mark:UnpooledHeapByteBuf(ridx: 0, widx: 3, cap: 5/5)
read:UnpooledHeapByteBuf(ridx: 2, widx: 3, cap: 5/5)
reset:UnpooledHeapByteBuf(ridx: 0, widx: 3, cap: 5/5)
有兴趣的可以看一下上一篇分享的ByteBuffer,对比一下,就能发现在Netty中通过独立的读写索引维护,避免读写模式的切换,更加方便了。
Handler的使用
前面介绍了Handler包含了Inbound和Outbound两种,他们统一放在一个双向链表中:
image当接收消息的时候,会从链表的表头开始遍历,如果是inbound就调用对应的方法;如果发送消息则从链表的尾巴开始遍历。那么上面途中的例子,接收消息就会输出:
InboundA --> InboundB --> InboundC
输出消息,则会输出:
OutboundC --> OutboundB --> OutboundA
这里有段代码,可以直接复制下来,试试看:
package cn.xingoo.book.netty.pipeline;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.nio.charset.Charset;
/**
* 注意:
*
* 1 ChannelOutboundHandler要在最后一个Inbound之前
*
*/
public class NettyNioServerHandlerTest {
final static ByteBuf buffer = Unpooled.unreleasableBuffer(Unpooled.copiedBuffer("Hi\r\n", Charset.forName("UTF-8")));
public void serve(int port) throws InterruptedException {
EventLoopGroup bossGroup = new NioEventLoopGroup(1);
EventLoopGroup workerGroup = new NioEventLoopGroup();
try{
ServerBootstrap b = new ServerBootstrap();
b.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class)
.localAddress(new InetSocketAddress(port))
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel socketChannel) throws Exception {
ChannelPipeline pipeline = socketChannel.pipeline();
pipeline.addLast("1",new InboundA());
pipeline.addLast("2",new OutboundA());
pipeline.addLast("3",new InboundB());
pipeline.addLast("4",new OutboundB());
pipeline.addLast("5",new OutboundC());
pipeline.addLast("6",new InboundC());
}
});
ChannelFuture f = b.bind().sync();
f.channel().closeFuture().sync();
} finally {
bossGroup.shutdownGracefully().sync();
workerGroup.shutdownGracefully().sync();
}
}
public static void main(String[] args) throws InterruptedException {
NettyNioServerHandlerTest server = new NettyNioServerHandlerTest();
server.serve(5555);
}
private static class InboundA extends ChannelInboundHandlerAdapter {
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
ByteBuf buf = (ByteBuf)msg;
System.out.println("InboundA read"+buf.toString(Charset.forName("UTF-8")));
super.channelRead(ctx, msg);
}
}
private static class InboundB extends ChannelInboundHandlerAdapter {
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
ByteBuf buf = (ByteBuf)msg;
System.out.println("InboundB read"+buf.toString(Charset.forName("UTF-8")));
super.channelRead(ctx, msg);
// 从pipeline的尾巴开始找outbound
ctx.channel().writeAndFlush(buffer);
}
}
private static class InboundC extends ChannelInboundHandlerAdapter {
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
ByteBuf buf = (ByteBuf)msg;
System.out.println("InboundC read"+buf.toString(Charset.forName("UTF-8")));
super.channelRead(ctx, msg);
// 这样会从当前的handler向前找outbound
//ctx.writeAndFlush(buffer);
}
}
private static class OutboundA extends ChannelOutboundHandlerAdapter {
@Override
public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
System.out.println("OutboundA write");
super.write(ctx, msg, promise);
}
}
private static class OutboundB extends ChannelOutboundHandlerAdapter {
@Override
public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
System.out.println("OutboundB write");
super.write(ctx, msg, promise);
}
}
private static class OutboundC extends ChannelOutboundHandlerAdapter {
@Override
public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
System.out.println("OutboundC write");
super.write(ctx, msg, promise);
}
}
}
网友评论