为什么要用Netty开发NIO程序
ＪＡＶＡ原生的ＮＩＯ程序包，不担编程麻烦，而且ＢＵＧ很多，性能差，所以就需要很多第三方工具包来实现ＮＩＯ网络通信。
Netty 是一个基于NIO的客户，服务器端编程框架，使用Netty 可以确保你快速和简单的开发出一个网络应用，例如实现了某种协议的客户，服务端应用。Netty相当简化和流线化了网络应用的编程开发过程，例如，TCP和UDP的socket服务开发。Netty现在版本是4.1，开发工具包下载链接：http://netty.io/downloads.html
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Reactor通信调度层
主要职责：监听网络的读写和连接操作，负责将网络层的数据读取到内存缓冲区中，然后触发各种网络事件，例如连接创建、连接激活、读事件、写事件等，将这些事件触发到Pipeline中，由Pipeline管理的职责链进行后续处理。
由一系列的辅助类完成，包括Reactor线程NioeventLoop以及父类、NioSocketChannel、ButeBuffer等。 -
职责链ChannelPipeline
负责事件在职责链中有序传播，同时负责动态地编排职责链。职责链可以选择监听和处理自己关心的事件，可以拦截处理和向后/向前传播事件。
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业务逻辑编排层（service ChannelHandler）
分为两类，一类是纯粹的业务逻辑编排，一类是其他的应用层协议插件。
下面是Ｎｅｔｔｙ开发的例子程序，运行环境Win10，JDK7，Netty4.1.6，程序功能从服务器端取得时间，在客户端显示
服务端：
package nettyTest;
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;
/**
* Discards any incoming data.
*/
public class DiscardServer {
private int port;
public DiscardServer(int port) {
this.port = port;
}
public void run() throws Exception {
EventLoopGroup bossGroup = new NioEventLoopGroup(); // (1)
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap b = new ServerBootstrap(); // (2)
b.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class) // (3)
.childHandler(new ChannelInitializer<SocketChannel>() { // (4)
@Override
public void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new TimeServerHandler());
}
})
.option(ChannelOption.SO_BACKLOG, 128) // (5)
.childOption(ChannelOption.SO_KEEPALIVE, true); // (6)
// Bind and start to accept incoming connections.
ChannelFuture f = b.bind(port).sync(); // (7)
System.out.println("Server Starting :"+port);
// Wait until the server socket is closed.
// In this example, this does not happen, but you can do that to gracefully
// shut down your server.
f.channel().closeFuture().sync();
} finally {
workerGroup.shutdownGracefully();
bossGroup.shutdownGracefully();
}
}
public static void main(String[] args) throws Exception {
int port;
if (args.length > 0) {
port = Integer.parseInt(args[0]);
} else {
port = 8080;
}
new DiscardServer(port).run();
}
}
====================================================================
package nettyTest;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
public class TimeServerHandler extends ChannelInboundHandlerAdapter {
@Override
public void channelActive(final ChannelHandlerContext ctx) { // (1)
final ByteBuf time = ctx.alloc().buffer(4); // (2)
time.writeInt((int) (System.currentTimeMillis() / 1000L + 2208988800L));
final ChannelFuture f = ctx.writeAndFlush(time); // (3)
System.out.println("Server return :"+time.toString());
f.addListener(new ChannelFutureListener() {
@Override
public void operationComplete(ChannelFuture future) {
assert f == future;
ctx.close();
}
}); // (4)
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
cause.printStackTrace();
ctx.close();
}
}
客户端程序：
package NET;
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 TimeClient {
public static void main(String[] args) throws Exception {
String host = "127.0.0.1";
int port = Integer.parseInt("8080");
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
Bootstrap b = new Bootstrap(); // (1)
b.group(workerGroup); // (2)
b.channel(NioSocketChannel.class); // (3)
b.option(ChannelOption.SO_KEEPALIVE, true); // (4)
b.handler(new ChannelInitializer<SocketChannel>() {
@Override
public void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new TimeClientHandler());
}
});
// Start the client.
ChannelFuture f = b.connect(host, port).sync(); // (5)
// Wait until the connection is closed.
f.channel().closeFuture().sync();
} finally {
workerGroup.shutdownGracefully();
}
}
}
====================================================================
package NET;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import java.util.Date;
public class TimeClientHandler extends ChannelInboundHandlerAdapter {
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) {
ByteBuf m = (ByteBuf) msg; // (1)
try {
long currentTimeMillis = (m.readUnsignedInt() - 2208988800L) * 1000L;
System.out.println(new Date(currentTimeMillis));
ctx.close();
} finally {
m.release();
}
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
cause.printStackTrace();
ctx.close();
}
}
运行结果：
服务器端输出：
Server Starting :8080
Server return :PooledUnsafeDirectByteBuf(freed)
客户端输出：
Thu Nov 03 17:03:20 CST 2016
====================================================================================
下面第二个程序，功能是建立一个服务器和客户端的聊天室
服务端程序：
package SecChat;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.example.telnet.TelnetServer;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import io.netty.handler.ssl.SslContext;
import io.netty.handler.ssl.SslContextBuilder;
import io.netty.handler.ssl.util.SelfSignedCertificate;
/**
* Simple SSL chat server modified from {@link TelnetServer}.
*/
public final class SecureChatServer {
static final int PORT = Integer.parseInt(System.getProperty("port", "8992"));
public static void main(String[] args) throws Exception {
SelfSignedCertificate ssc = new SelfSignedCertificate();
SslContext sslCtx = SslContextBuilder.forServer(ssc.certificate(), ssc.privateKey())
.build();
EventLoopGroup bossGroup = new NioEventLoopGroup(1);
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap b = new ServerBootstrap();
b.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class)
.handler(new LoggingHandler(LogLevel.INFO))
.childHandler(new SecureChatServerInitializer(sslCtx));
b.bind(PORT).sync().channel().closeFuture().sync();
} finally {
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
}
====================================================================================
package SecChat;
import io.netty.channel.Channel;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.channel.group.ChannelGroup;
import io.netty.channel.group.DefaultChannelGroup;
import io.netty.handler.ssl.SslHandler;
import io.netty.util.concurrent.Future;
import io.netty.util.concurrent.GenericFutureListener;
import io.netty.util.concurrent.GlobalEventExecutor;
import java.net.InetAddress;
/**
* Handles a server-side channel.
*/
public class SecureChatServerHandler extends SimpleChannelInboundHandler<String> {
static final ChannelGroup channels = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);
@Override
public void channelActive(final ChannelHandlerContext ctx) {
// Once session is secured, send a greeting and register the channel to the global channel
// list so the channel received the messages from others.
ctx.pipeline().get(SslHandler.class).handshakeFuture().addListener(
new GenericFutureListener<Future<Channel>>() {
@Override
public void operationComplete(Future<Channel> future) throws Exception {
ctx.writeAndFlush(
"Welcome to " + InetAddress.getLocalHost().getHostName() + " secure chat service!\n");
ctx.writeAndFlush(
"Your session is protected by " +
ctx.pipeline().get(SslHandler.class).engine().getSession().getCipherSuite() +
" cipher suite.\n");
channels.add(ctx.channel());
}
});
}
@Override
public void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
// Send the received message to all channels but the current one.
for (Channel c: channels) {
if (c != ctx.channel()) {
c.writeAndFlush("[" + ctx.channel().remoteAddress() + "] " + msg + '\n');
} else {
c.writeAndFlush("[you] " + msg + '\n');
}
System.out.println("Server recieve:"+msg);
}
// Close the connection if the client has sent 'bye'.
if ("bye".equals(msg.toLowerCase())) {
ctx.close();
}
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
cause.printStackTrace();
ctx.close();
}
}
====================================================================================
package SecChat;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
import io.netty.handler.codec.DelimiterBasedFrameDecoder;
import io.netty.handler.codec.Delimiters;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;
import io.netty.handler.ssl.SslContext;
/**
* Creates a newly configured {@link ChannelPipeline} for a new channel.
*/
public class SecureChatServerInitializer extends ChannelInitializer<SocketChannel> {
private final SslContext sslCtx;
public SecureChatServerInitializer(SslContext sslCtx) {
this.sslCtx = sslCtx;
}
@Override
public void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
// Add SSL handler first to encrypt and decrypt everything.
// In this example, we use a bogus certificate in the server side
// and accept any invalid certificates in the client side.
// You will need something more complicated to identify both
// and server in the real world.
pipeline.addLast(sslCtx.newHandler(ch.alloc()));
// On top of the SSL handler, add the text line codec.
pipeline.addLast(new DelimiterBasedFrameDecoder(8192, Delimiters.lineDelimiter()));
pipeline.addLast(new StringDecoder());
pipeline.addLast(new StringEncoder());
// and then business logic.
pipeline.addLast(new SecureChatServerHandler());
}
}
====================================================================================
客户端程序：
package SecChat;
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.example.telnet.TelnetClient;
import io.netty.handler.ssl.SslContext;
import io.netty.handler.ssl.SslContextBuilder;
import io.netty.handler.ssl.util.InsecureTrustManagerFactory;
import java.io.BufferedReader;
import java.io.InputStreamReader;
/**
* Simple SSL chat client modified from {@link TelnetClient}.
*/
public final class SecureChatClient {
static final String HOST = System.getProperty("host", "127.0.0.1");
static final int PORT = Integer.parseInt(System.getProperty("port", "8992"));
public static void main(String[] args) throws Exception {
// Configure SSL.
final SslContext sslCtx = SslContextBuilder.forClient()
.trustManager(InsecureTrustManagerFactory.INSTANCE).build();
EventLoopGroup group = new NioEventLoopGroup();
try {
Bootstrap b = new Bootstrap();
b.group(group)
.channel(NioSocketChannel.class)
.handler(new SecureChatClientInitializer(sslCtx));
// Start the connection attempt.
Channel ch = b.connect(HOST, PORT).sync().channel();
// Read commands from the stdin.
ChannelFuture lastWriteFuture = null;
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
for (;;) {
String line = in.readLine();
if (line == null) {
break;
}
// Sends the received line to the server.
lastWriteFuture = ch.writeAndFlush(line + "\r\n");
// If user typed the 'bye' command, wait until the server closes
// the connection.
if ("bye".equals(line.toLowerCase())) {
ch.closeFuture().sync();
break;
}
}
// Wait until all messages are flushed before closing the channel.
if (lastWriteFuture != null) {
lastWriteFuture.sync();
}
} finally {
// The connection is closed automatically on shutdown.
group.shutdownGracefully();
}
}
}
====================================================================================
package SecChat;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
/**
* Handles a client-side channel.
*/
public class SecureChatClientHandler extends SimpleChannelInboundHandler<String> {
@Override
public void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
System.err.println(msg);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
cause.printStackTrace();
ctx.close();
}
}
====================================================================================
package SecChat;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.socket.SocketChannel;
import io.netty.handler.codec.DelimiterBasedFrameDecoder;
import io.netty.handler.codec.Delimiters;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;
import io.netty.handler.ssl.SslContext;
/**
* Creates a newly configured {@link ChannelPipeline} for a new channel.
*/
public class SecureChatClientInitializer extends ChannelInitializer<SocketChannel> {
private final SslContext sslCtx;
public SecureChatClientInitializer(SslContext sslCtx) {
this.sslCtx = sslCtx;
}
@Override
public void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
// Add SSL handler first to encrypt and decrypt everything.
// In this example, we use a bogus certificate in the server side
// and accept any invalid certificates in the client side.
// You will need something more complicated to identify both
// and server in the real world.
pipeline.addLast(sslCtx.newHandler(ch.alloc(), SecureChatClient.HOST, SecureChatClient.PORT));
// On top of the SSL handler, add the text line codec.
pipeline.addLast(new DelimiterBasedFrameDecoder(8192, Delimiters.lineDelimiter()));
pipeline.addLast(new StringDecoder());
pipeline.addLast(new StringEncoder());
// and then business logic.
pipeline.addLast(new SecureChatClientHandler());
}
}
====================================================================================
程序运行结果（注意这是个交互的界面，客户端可以输入聊天的内容）：
服务器端输出：
十一月 04, 2016 1:37:21 下午 io.netty.handler.logging.LoggingHandler channelRegistered
信息: [id: 0x0b0140a6] REGISTERED
十一月 04, 2016 1:37:21 下午 io.netty.handler.logging.LoggingHandler bind
信息: [id: 0x0b0140a6] BIND: 0.0.0.0/0.0.0.0:8992
十一月 04, 2016 1:37:21 下午 io.netty.handler.logging.LoggingHandler channelActive
信息: [id: 0x0b0140a6, L:/0:0:0:0:0:0:0:0:8992] ACTIVE
十一月 04, 2016 1:37:42 下午 io.netty.handler.logging.LoggingHandler channelRead
信息: [id: 0x0b0140a6, L:/0:0:0:0:0:0:0:0:8992] RECEIVED: [id: 0xe31c8862, L:/127.0.0.1:8992 - R:/127.0.0.1:49653]
Server recieve:
Server recieve:ni hao ,Tom !
客户端输出：
Welcome to USER-20150114VP secure chat service!
Your session is protected by TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA cipher suite.
[you]
ni hao ,Tom !
[you] ni hao ,Tom !