什么是Netty
Netty 是一个利用 Java 的高级网络的能力，隐藏其背后的复杂性而提供一个易于使用的 API 的客户端/服务器框架。
Netty 是一个广泛使用的 Java 网络编程框架（Netty 在 2011 年获得了Duke's Choice Award，见https://www.java.net/dukeschoice/2011）。
它活跃和成长于用户社区，像大型公司 Facebook 和 Instagram 以及流行
开源项目如 Infinispan, HornetQ, Vert.x, Apache Cassandra 和 Elasticsearch 等，
都利用其强大的对于网络抽象的核心代码。
以上是摘自《Essential Netty In Action》这本书，本文的内容也是本人读了这本书之后的一些整理心得，如有不当之处欢迎大虾们指正
Netty和Tomcat有什么区别？
Netty和Tomcat最大的区别就在于通信协议，Tomcat是基于Http协议的，他的实质是一个基于http协议的web容器，但是Netty不一样，他能通过编程自定义各种协议，因为netty能够通过codec自己来编码/解码字节流，完成类似redis访问的功能，这就是netty和tomcat最大的不同。
有人说netty的性能就一定比tomcat性能高，其实不然，tomcat从6.x开始就支持了nio模式，并且后续还有arp模式——一种通过jni调用apache网络库的模式，相比于旧的bio模式，并发性能得到了很大提高，特别是arp模式，而netty是否比tomcat性能更高，则要取决于netty程序作者的技术实力了。
Netty为什么并发高
Netty是一款基于NIO（Nonblocking I/O，非阻塞IO）开发的网络通信框架，对比于BIO（Blocking I/O，阻塞IO），他的并发性能得到了很大提高
五种常见的IO模型
- BIO，同步阻塞IO，阻塞整个步骤，如果连接少，他的延迟是最低的，因为一个线程只处理一个连接，适用于少连接且延迟低的场景，比如说数据库连接
- NIO，同步非阻塞IO，阻塞业务处理但不阻塞数据接收，适用于高并发且处理简单的场景，比如聊天软件
- 多路复用IO，他的两个步骤处理是分开的，也就是说，一个连接可能他的数据接收是线程a完成的，数据处理是线程b完成的，他比BIO能处理更多请求，但是比不上NIO，但是他的处理性能又比BIO更差，因为一个连接他需要两次system call，而BIO只需要一次，所以这种IO模型应用的不多
- 信号驱动IO，这种IO模型主要用在嵌入式开发，不参与讨论
- 异步IO，他的数据请求和数据处理都是异步的，数据请求一次返回一次，适用于长连接的业务场景
内容摘自Linux IO模式及 select、poll、epoll详解
三种IO模式代码比较
- 阻塞IO
public class PlainOioServer {
public void serve(int port) throws IOException {
final ServerSocket socket = new ServerSocket(port); //1
try {
for (;;) {
final Socket clientSocket = socket.accept(); //2
System.out.println("Accepted connection from " + clientSocket);
new Thread(new Runnable() { //3
@Override
public void run() {
OutputStream out;
try {
out = clientSocket.getOutputStream();
out.write("Hi!\r\n".getBytes(Charset.forName("UTF-8"))); //4
out.flush();
clientSocket.close(); //5
} catch (IOException e) {
e.printStackTrace();
try {
clientSocket.close();
} catch (IOException ex) {
// ignore on close
}
}
}
}).start(); //6
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
- 非阻塞IO （NIO）
public class PlainNioServer {
public void serve(int port) throws IOException {
ServerSocketChannel serverChannel = ServerSocketChannel.open();
serverChannel.configureBlocking(false);
ServerSocket ss = serverChannel.socket();
InetSocketAddress address = new InetSocketAddress(port);
ss.bind(address); //1
Selector selector = Selector.open(); //2
serverChannel.register(selector, SelectionKey.OP_ACCEPT); //3
final ByteBuffer msg = ByteBuffer.wrap("Hi!\r\n".getBytes());
for (;;) {
try {
selector.select(); //4
} catch (IOException ex) {
ex.printStackTrace();
// handle exception
break;
}
Set<SelectionKey> readyKeys = selector.selectedKeys(); //5
Iterator<SelectionKey> iterator = readyKeys.iterator();
while (iterator.hasNext()) {
SelectionKey key = iterator.next();
iterator.remove();
try {
if (key.isAcceptable()) { //6
ServerSocketChannel server =
(ServerSocketChannel)key.channel();
SocketChannel client = server.accept();
client.configureBlocking(false);
client.register(selector, SelectionKey.OP_WRITE |
SelectionKey.OP_READ, msg.duplicate()); //7
System.out.println(
"Accepted connection from " + client);
}
if (key.isWritable()) { //8
SocketChannel client =
(SocketChannel)key.channel();
ByteBuffer buffer =
(ByteBuffer)key.attachment();
while (buffer.hasRemaining()) {
if (client.write(buffer) == 0) { //9
break;
}
}
client.close(); //10
}
} catch (IOException ex) {
key.cancel();
try {
key.channel().close();
} catch (IOException cex) {
// 在关闭时忽略
}
}
}
}
}
}
- netty 实现
public class NettyOioServer {
public void server(int port) throws Exception {
final ByteBuf buf = Unpooled.unreleasableBuffer(
Unpooled.copiedBuffer("Hi!\r\n", Charset.forName("UTF-8")));
EventLoopGroup group = new OioEventLoopGroup();
try {
ServerBootstrap b = new ServerBootstrap(); //1
b.group(group) //2
.channel(OioServerSocketChannel.class)
.localAddress(new InetSocketAddress(port))
.childHandler(new ChannelInitializer<SocketChannel>() {//3
@Override
public void initChannel(SocketChannel ch)
throws Exception {
ch.pipeline().addLast(new ChannelInboundHandlerAdapter() { //4
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
ctx.writeAndFlush(buf.duplicate()).addListener(ChannelFutureListener.CLOSE);//5
}
});
}
});
ChannelFuture f = b.bind().sync(); //6
f.channel().closeFuture().sync();
} finally {
group.shutdownGracefully().sync(); //7
}
}
}
netty 功能点介绍
- Channel 表示一个连接通道，可以理解为每一个请求，就是一个Channel
- ChanelHandler 处理业务
- ChannelHandlerContext 用于传输业务数据
- ChannelPipeline 用于保存处理过程需要用到的ChannelHandler和ChannelHandlerContext
动手搭建Netty实战
- TCP服务处理代码
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import org.apache.log4j.Logger;
/**
* @author create by yingjie.chen on 2018/3/26.
* @version 2018/3/26 17:03
*/
public class TcpServerHandler extends SimpleChannelInboundHandler<Object>{
private static final Logger logger = Logger.getLogger(TcpServerHandler.class);
@Override
protected void channelRead0(ChannelHandlerContext ctx, Object msg) throws Exception {
logger.info("SERVER接收到消息:"+msg);
ctx.channel().writeAndFlush("yes, server is accepted you ,nice !"+msg);
}
}
- TCP服务端
import org.apache.log4j.Logger;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.LengthFieldBasedFrameDecoder;
import io.netty.handler.codec.LengthFieldPrepender;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;
import io.netty.util.CharsetUtil;
/**
* @author create by yingjie.chen on 2018/3/26.
* @version 2018/3/26 17:07
*/
public class TcpServer {
private static final Logger logger = Logger.getLogger(TcpServer.class);
private static final String IP = "127.0.0.1";
private static final int PORT = 9999;
/**用于分配处理业务线程的线程组个数 */
protected static final int BIZGROUPSIZE = Runtime.getRuntime().availableProcessors()*2; //默认
/** 业务出现线程大小*/
protected static final int BIZTHREADSIZE = 4;
/*
* NioEventLoopGroup实际上就是个线程池,
* NioEventLoopGroup在后台启动了n个NioEventLoop来处理Channel事件,
* 每一个NioEventLoop负责处理m个Channel,
* NioEventLoopGroup从NioEventLoop数组里挨个取出NioEventLoop来处理Channel
*/
private static final EventLoopGroup bossGroup = new NioEventLoopGroup(BIZGROUPSIZE);
private static final EventLoopGroup workerGroup = new NioEventLoopGroup(BIZTHREADSIZE);
protected static void run() throws Exception {
ServerBootstrap b = new ServerBootstrap();
b.group(bossGroup, workerGroup);
b.channel(NioServerSocketChannel.class);
b.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
public void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast("frameDecoder", new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE, 0, 4, 0, 4));
pipeline.addLast("frameEncoder", new LengthFieldPrepender(4));
pipeline.addLast("decoder", new StringDecoder(CharsetUtil.UTF_8));
pipeline.addLast("encoder", new StringEncoder(CharsetUtil.UTF_8));
pipeline.addLast(new TcpServerHandler());
}
});
b.bind(IP, PORT).sync();
logger.info("TCP服务器已启动");
}
protected static void shutdown() {
workerGroup.shutdownGracefully();
bossGroup.shutdownGracefully();
}
public static void main(String[] args) throws Exception {
logger.info("开始启动TCP服务器...");
TcpServer.run();
// TcpServer.shutdown();
}
}
- TCP客户端处理代码
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import org.apache.log4j.Logger;
/**
* @author create by yingjie.chen on 2018/3/26.
* @version 2018/3/26 17:08
*/
public class TcpClientHandler extends SimpleChannelInboundHandler<Object> {
private static final Logger logger = Logger.getLogger(TcpClientHandler.class);
@Override
protected void channelRead0(ChannelHandlerContext ctx, Object msg)
throws Exception {
//messageReceived方法,名称很别扭，像是一个内部方法.
logger.info("client接收到服务器返回的消息:"+msg);
}
}
- TCP客户端
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.LengthFieldBasedFrameDecoder;
import io.netty.handler.codec.LengthFieldPrepender;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;
import io.netty.util.CharsetUtil;
import org.apache.log4j.Logger;
/**
* @author create by yingjie.chen on 2018/3/26.
* @version 2018/3/26 17:08
*/
public class TcpClient {
private static final Logger logger = Logger.getLogger(TcpClient.class);
public static String HOST = "127.0.0.1";
public static int PORT = 9999;
public static Bootstrap bootstrap = getBootstrap();
public static Channel channel = getChannel(HOST,PORT);
/**
* 初始化Bootstrap
* @return
*/
public static final Bootstrap getBootstrap(){
EventLoopGroup group = new NioEventLoopGroup();
Bootstrap b = new Bootstrap();
b.group(group).channel(NioSocketChannel.class);
b.handler(new ChannelInitializer<Channel>() {
@Override
protected void initChannel(Channel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
pipeline.addLast("frameDecoder", new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE, 0, 4, 0, 4));
pipeline.addLast("frameEncoder", new LengthFieldPrepender(4));
pipeline.addLast("decoder", new StringDecoder(CharsetUtil.UTF_8));
pipeline.addLast("encoder", new StringEncoder(CharsetUtil.UTF_8));
pipeline.addLast("handler", new TcpClientHandler());
}
});
b.option(ChannelOption.SO_KEEPALIVE, true);
return b;
}
public static final Channel getChannel(String host,int port){
Channel channel = null;
try {
channel = bootstrap.connect(host, port).sync().channel();
} catch (Exception e) {
logger.error(String.format("连接Server(IP[%s],PORT[%s])失败", host,port),e);
return null;
}
return channel;
}
public static void sendMsg(String msg) throws Exception {
if(channel!=null){
channel.writeAndFlush(msg).sync();
}else{
logger.warn("消息发送失败,连接尚未建立!");
}
}
public static void main(String[] args) throws Exception {
try {
long t0 = System.nanoTime();
for (int i = 0; i < 100000; i++) {
TcpClient.sendMsg(i+"你好1");
}
long t1 = System.nanoTime();
System.out.println((t1-t0)/1000000.0);
} catch (Exception e) {
e.printStackTrace();
}
}
}
