• 传统的同步阻塞式I/O编程
  • 基于NIO的非阻塞编程
  • 基于NIO2.0的异步非阻塞(AIO)编程
  • 为什么要使用NIO编程
  • 为什么选择Netty

  第二章 NIO 入门

    2.1 传统的BIO编程

      2.1.1 BIO 通信模型图

      2.1.2 同步阻塞式I/O创建的TimeServer源码分析

package com.phei.netty.bio;

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket; public class TimeServer {
public static void main(String[] args)throws IOException{
int port = 8080;
if(args != null && args.length > 0){
try{
port = Integer.valueOf(port);
}catch(NumberFormatException e){
// port = 8080;
}
}
ServerSocket server = null;
try{
// 如果端口合法且没有被占用,服务端监听成功
server = new ServerSocket(port);
System.out.println("The time server is start in port:" + port);
Socket socket = null;
while(true){
// 如果没有客户端接入,则主线程阻塞在ServerSocket的accept操作上
socket = server.accept();
new Thread(new TimeServerHandler(socket)).start();
}
}finally{
if(server != null){
System.out.println("The time server close");
server.close();
server = null;
}
}
}
}
package com.phei.netty.bio;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.Date; public class TimeServerHandler implements Runnable { private Socket socket; public TimeServerHandler() {
// TODO Auto-generated constructor stub
} public TimeServerHandler(Socket socket) {
super();
this.socket = socket;
} @Override
public void run() {
BufferedReader in = null;
PrintWriter out = null;
try{
// 输入流,获取客户端输出流信息
in = new BufferedReader(new InputStreamReader(this.socket.getInputStream()));
// 输出流,放到客户端输入流中
out = new PrintWriter(this.socket.getOutputStream(),true);
String currentTime = null;
String body = null;
while(true){
// 获取客户端输出的信息
body = in.readLine();
if(body == null){
break;
}
System.out.println("The time server receive order : " + body);
currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body)?new Date(System.currentTimeMillis()).toString():"BAD ORDER";
// 发送信息到客户端输入流中
out.println(currentTime);
}
}catch(Exception e){
if(in != null){
try{
in.close();
}catch(IOException e1){
e1.printStackTrace();
}
}
if(out != null){
out.close();
out = null;
}
if(this.socket != null){
try{
this.socket.close();
}catch(IOException e1){
e1.printStackTrace();
}
this.socket = null;
}
}
} }

      2.1.3 同步阻塞式I/O创建的TimeClient源码分析

package com.phei.netty.bio;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket; public class TimeClient { public static void main(String[] args){
int port = 8080;
if(args != null && args.length > 0){
try{
port = Integer.valueOf(args[0]);
}catch(NumberFormatException e){ }
}
Socket socket = null;
BufferedReader in = null;
PrintWriter out = null;
try{
socket = new Socket("127.0.0.1",port);
// 输入流,获取服务端输出流信息
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
// 输出流,放到服务端输入流中
out = new PrintWriter(socket.getOutputStream(),true);
// 发送信息到服务端
out.println("QUERY TIME ORDER");
System.out.println("Send order 2 server succeed.");
// 读取输入流的信息
String resp = in.readLine();
System.out.println("Now is : " + resp);
}catch(Exception e){ }finally{
if(out != null){
out.close();
out = null;
}
if(in != null){
try{
in.close();
}catch(IOException e){
e.printStackTrace();
}
in = null;
}
if(socket != null){
try{
socket.close();
}catch(IOException e){
e.printStackTrace();
}
socket = null;
}
}
}
}

    2.2 伪异步I/O编程

      2.2.1 伪异步I/O模型图

      2.2.2 伪异步I/O创建的TimeServer源码分析

package com.phei.netty.pio;

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket; import com.phei.netty.bio.TimeServerHandler; public class TimeServer { public static void main(String[] args) throws IOException{
int port = 8080;
if(args != null && args.length > 0){
try{
port = Integer.valueOf(args[0]);
}catch(NumberFormatException e){ }
}
ServerSocket server = null;
try{
server = new ServerSocket(port);
System.out.println("The time server is start in port:" + port);
Socket socket = null;
//创建I/O任务线程池
TimeServerHandlerExecutePool singleExecutor = new TimeServerHandlerExecutePool(50,10000);
while(true){
socket = server.accept();
// 当接收到新的客户端连接时,将请求Socket封装成一个Task,然后调用线程池的execute方法执行,从而避免了每个请求接入都创建一个新的线程。
singleExecutor.execute(new TimeServerHandler(socket));
}
}finally{
if(server != null){
System.out.println("The time server close");
server.close();
server = null;
}
}
}
}
package com.phei.netty.pio;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit; public class TimeServerHandlerExecutePool {
private ExecutorService executor; public TimeServerHandlerExecutePool(int maxPoolSize,int queueSize){
executor =
new ThreadPoolExecutor(Runtime.getRuntime().availableProcessors(), maxPoolSize, 120L, TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(queueSize));
}
public void execute(Runnable task){
executor.execute(task);
}
}

      2.2.3 伪异步I/O弊端分析

    2.3 NIO编程

      2.3.1 NIO类库简介

        1.缓冲区Buffer

          ByteBuffer

          CharBuffer

          ShortBuffer

          IntBuffer

          LongBuffer

          FloatBuffer

          DoubleBuffer

        2.通道Channel

          网络读写:SelectableChannel

          文件操作:FileChannel

        3.多路复用器Selector

          多路复用器提供选择已经就绪的任务的能力:Selector回不断地轮询注册在其上的Channel,如果某个Channel上面发生读或者写时间,这个Channel就处                               于就绪状态,会被Selector轮询出来,然后通过SelectionKey可以获取就绪Channel的集合,进行后续的I/O操作。

      2.3.2 NIO服务端序列图

      2.3.3 NIO创建的TimeServer源码分析

package com.phei.netty.nio;

public class TimeServer {
public static void main(String[] args){
int port = 8080;
if(args != null && args.length > 0){
try{
port = Integer.valueOf(args[0]);
}catch(NumberFormatException e){ }
}
// 创建多路复用类MultiplexerTimeServer。它是一个独立的线程,负责轮询多路复用器Selctor,可以处理多个客户端的并发接入。
MultiplexerTimeServer timeServer = new MultiplexerTimeServer(port);
new Thread(timeServer,"NIO-MultiplexerTimeServer-001").start();
}
}
package com.phei.netty.nio;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Date;
import java.util.Iterator;
import java.util.Set; public class MultiplexerTimeServer implements Runnable { private Selector selector;
private ServerSocketChannel servChannel;
private volatile boolean stop; /*
* 初始化多路复用器,绑定监听端口
* 在构造方法中创建多路复用器Selector、ServerSocketChannel,对Channel和TCP参数进行配置。
* 将ServlerSocketChannel设置为异步非阻塞模式,它的backlog设为1024。
* 系统资源初始化成功后,将ServerSocketChannel注册到Selector,监听SelectionKey.OP_ACCEPT操作位。
* 如果资源初始化失败,则退出。
*/
public MultiplexerTimeServer(int port){
try{
//Opens a selector.
selector = Selector.open();
//Opens a server-socket channel.
servChannel = ServerSocketChannel.open();
// Adjusts this channel's non-blocking mode.
servChannel.configureBlocking(false);
// Retrieves a server socket associated with this channel.
// Binds the ServerSocket to a specific address (IP address and port number).
// 1024 : requested maximum length of the queue of incoming connections.
servChannel.socket().bind(new InetSocketAddress(port),1024);
// Registers this channel with the given selector, returning a selection key.
// SelectionKey.OP_ACCEPT : Operation-set bit for socket-accept operations.
servChannel.register(selector,SelectionKey.OP_ACCEPT);
System.out.println("The time server is start in port:" + port);
}catch(IOException e){
e.printStackTrace();
System.exit(1);
}
} public void stop(){
this.stop = true;
} /**
* 在线程的run方法的while循环体中循环遍历selector,它的休眠时间为1s。
* 无论是否有读写等事件发生,selector每隔1s都被唤醒一次。
* selector也提供了一个无参的select方法:当有处于就绪状态的Channel时,selector将返回该Channel的SelectionKey集合。
* 通过对就绪状态的Channel集合进行迭代,可以进行网络的异步读写操作。
*/
@Override
public void run() {
while(!stop){
try{
// Selects a set of keys whose corresponding channels are ready for I/O operations.
// timeout - If positive, block for up to timeout milliseconds, more or less, while waiting for a channel to become ready;
//          if zero, block indefinitely; must not be negative
selector.select(1000);
// Returns this selector's selected-key set.
Set<SelectionKey> selectedKeys = selector.selectedKeys();
Iterator<SelectionKey> it = selectedKeys.iterator();
SelectionKey key = null;
while(it.hasNext()){
key = it.next();
it.remove();
try{
handleInput(key);
}catch(Exception e){
if(key != null){
// Requests that the registration of this key's channel with its selector be cancelled.
key.cancel();
if(key.channel() != null){
key.channel().close();
}
}
}
}
}catch (Throwable t) {
t.printStackTrace();
}
}
// 多路复用器关闭后,所有注册在上面的Channel和Pipe等资源都会被自动去注册并关闭,所以不需要重复释放资源
if(selector != null){
try{
selector.close();
}catch(IOException e){
e.printStackTrace();
}
}
}
/*
* 处理新接入的客户端请求信息,根据SelectionKey的操作位进行判断即可获知网络时间的类型,
* 通过ServerSocketChannel的accept接收客户端的连接请求并创建SocketChannel实例。
* 完成之后相当于完成了TCP的三次握手,TCP物理链路正是建立。
* 需要将新创建的SocketChannel设置为异步非阻塞,同时也可以对其TCP参数进行设置,如TCP接收和发送缓冲区的大小等。
*/
private void handleInput(SelectionKey key) throws IOException{
// Tells whether or not this key is valid.
if(key.isValid()){
// Tests whether this key's channel is ready to accept a new socket connection.
// 处理新接入的请求消息
if(key.isAcceptable()){
// Returns the channel for which this key was created.
ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
// Accepts a connection made to this channel's socket.
SocketChannel sc = ssc.accept();
// Adjusts this channel's blocking mode.
sc.configureBlocking(false);
// Registers this channel with the given selector, returning a selection key.
// The interest set for the resulting key
sc.register(selector, SelectionKey.OP_READ);
}
/*
* 用于读取客户端的请求消息。
* 首先创建一个ByteBuffer,由于事先无法得知客户端发送的码流大小,作为历程,开辟一个1MB的缓冲区。
* 然后调用SocketChannel的read方法读取请求码流。
*/
// Tests whether this key's channel is ready for reading.
if(key.isReadable()){
SocketChannel sc = (SocketChannel) key.channel();
// Allocates a new byte buffer.
ByteBuffer readBuffer = ByteBuffer.allocate(1024);
// Reads a sequence of bytes from this channel into the given buffer.
int readBytes =sc.read(readBuffer);
if(readBytes > 0){
// 对readBuffer进行flip操作,将缓冲区当前的limit设置为position,position设置为0,用于后续对缓冲区的读取操作。
// Flips this buffer.
readBuffer.flip();
// 根据缓冲区刻度的字节个数创建字节数组
// Returns the number of elements between the current position and the limit.
byte[] bytes = new byte[readBuffer.remaining()];
// 调用ByteBuffer的get操作将缓冲区可读字节数组复制到新创建的字节数组中
// Relative bulk get method.
readBuffer.get(bytes);
String body = new String(bytes,"UTF-8");
System.out.println("The time server receive order : " + body);
String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body)?new Date(System.currentTimeMillis()).toString():"BAD ORDER";
doWrite(sc,currentTime);
}else if(readBytes < 0){
// 对端链路关闭
key.cancel();
sc.close();
}else{
// 读到0字节,忽略
;
}
}
}
}
/*
* 将应答消息异步发送给客户端。
* 由于SocketChannel是异步非阻塞的,它并不保证一次能够把需要发送的字节数组发送完,此时会出现“写半包”问题。
* 需要注册写操作,不断轮询Selector将没有发送完的ByteBuffer发送完毕,
* 然后可以通过ByteBuffer的hasRemain()方法判断消息是否发送完成。
*/
private void doWrite(SocketChannel channel,String response) throws IOException{
if(response != null && response.trim().length() > 0){
byte[] bytes = response.getBytes();
ByteBuffer writeBuffer = ByteBuffer.allocate(bytes.length);
// Relative bulk put method (optional operation).
writeBuffer.put(bytes);
writeBuffer.flip();
// 调用SocketChannel的write方法将缓冲区中的字节数组发送出去
// Writes a sequence of bytes to this channel from the given buffer.
channel.write(writeBuffer);
}
}
}

      2.3.4 NIO客户端序列图

      2.3.5 NIO创建的TimeClient源码分析

package com.phei.netty.nio;

public class TimeClient {

    public static void main(String[] args){
int port = 8080;
if(args != null && args.length > 0){
try{
port = Integer.valueOf(args[0]);
}catch(NumberFormatException e){ }
}
new Thread(new TimeClientHandle("127.0.0.1",port),"TimeClient-001").start();
}
}
package com.phei.netty.nio;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.Set; public class TimeClientHandle implements Runnable { private String host;
private int port;
private Selector selector;
private SocketChannel socketChannel;
private volatile boolean stop; public TimeClientHandle() {
super();
// TODO Auto-generated constructor stub
} /*
* 使用构造函数初始化NIO的多路复用器和SocketChannel对象。
* 创建SocketChannel之后将其设置为异步非阻塞模式。
* 在此可以设置SocketChannel的TCP参数
*/
public TimeClientHandle(String string, int port) {
this.host = host == null ? "127.0.0.1" : host;
this.port = port;
try{
selector = Selector.open();
socketChannel = SocketChannel.open();
socketChannel.configureBlocking(false);
}catch(IOException e){
e.printStackTrace();
System.exit(1);
}
} /*
* 作为示例,连接是成功的,所以不需要做重连操作,因此将其放到循环之前。
*/
@Override
public void run() {
try{
// 如果连接成功、如果没有成功
doConnect();
}catch(IOException e){
e.printStackTrace();
System.exit(1);
}
// 轮询多路复用器Selector。当有就绪的Channel时,执行handleInput(key)方法。
while(!stop){
try{
selector.select(1000);
Set<SelectionKey> selectedKeys = selector.selectedKeys();
Iterator<SelectionKey> it = selectedKeys.iterator();
SelectionKey key = null;
while(it.hasNext()){
key = it.next();
it.remove();
try{
// 当有就绪的Channel时执行
handleInput(key);
}catch(Exception e){
if(key != null){
key.cancel();
if(key.channel() != null){
key.channel().close();
}
}
}
}
}catch(Exception e){
e.printStackTrace();
System.exit(1);
}
}
// 多路复用器关闭后,所有注册在上面的Channel和Pipe等资源都会被自动去注册并关闭,所以不需要重复释放资源
if(selector != null){
try{
selector.close();
}catch(IOException e){
e.printStackTrace();
}
}
} private void handleInput(SelectionKey key) throws IOException{
// Tells whether or not this key is valid.
if(key.isValid()){
// Returns the channel for which this key was created.
SocketChannel sc = (SocketChannel) key.channel();
// 判断是否连接成功
// 如果处于连接状态,说明服务端已经返回ACK应答消息。
// Tests whether this key's channel has either finished, or failed to finish,
// its socket-connection operation.
if(key.isConnectable()){
// 调用SecoketChannel的finishConnect()方法。
// 如果返回值为true,说明客户端连接成功;
// 如果返回值为false或者抛出IOException,说明连接失败
// Finishes the process of connecting a socket channel.
if(sc.finishConnect()){
// 将SocketChannel注册到多路复用器上,注册SelectionKey.OP_READ操作位,监听网络读操作,
// 然后发送请求消息给服务端
sc.register(selector, SelectionKey.OP_READ);
// 构造请求消息体,然后对其编码,写入到发送缓冲区中,最后调用SocketChannel的write方法进行发送。存在"半包写"
// 最后通过hasRemaining()方法对发送结果进行判断
doWrite(sc);
}else{
System.exit(1);//连接失败,进程退出
}
      }
// 测试此键的通道是否已准备好进行读取。
if(key.isReadable()){
ByteBuffer readBuffer = ByteBuffer.allocate(1024);
// 将字节序列从此通道读入给定的缓冲区。
int readBytes = sc.read(readBuffer);
if(readBytes > 0){
// 反转此缓冲区。
readBuffer.flip();
// 返回当前位置与限制之间的元素数。
byte[] bytes = new byte[readBuffer.remaining()];
readBuffer.get(bytes);
String body = new String(bytes,"UTF-8");
System.out.println("Now is : " + body);
this.stop = true;
}else if(readBytes < 0){
//对端链路关闭
key.cancel();
sc.close();
}else{
; //读到0字节,忽略
}
}
}
} private void doConnect() throws IOException{
// 如果直接连接成功,则注册到多路复用器上,发送请求消息,读应答
// 连接此通道的套接字
if(socketChannel.connect(new InetSocketAddress(host, port))){
// 连接成功,将SocketChannel注册到多路复用器Selector上,注册SelectionKey.OP_READ
socketChannel.register(selector, SelectionKey.OP_READ);
doWrite(socketChannel);
}else{
// 如果没有直接连接成功,则说明服务端没有返回TCP握手应答,但这并不代表连接失败。
// 需要将SocketChannel注册到多路复用器Selector上,注册SelectionKey.OP_CONNECT,
// 当服务端返回TCP syn-ack 消息后,Selector就能够轮询到这个SocketChannel处于连接就绪状态。
socketChannel.register(selector, SelectionKey.OP_CONNECT);
}
} private void doWrite(SocketChannel sc) throws IOException{
byte[] req = "QUERY TIME ORDER".getBytes();
// 分配一个新的字节缓冲区。
ByteBuffer writeBuffer = ByteBuffer.allocate(req.length);
writeBuffer.put(req);
writeBuffer.flip();
// 将字节序列从给定的缓冲区中写入此通道。
sc.write(writeBuffer);
// 告知在当前位置和限制之间是否有元素。
if(!writeBuffer.hasRemaining()){
// 如果缓冲区中的消息全部发送完成,打印
System.out.println("Send order 2 server succeed.");
}
}
}

     服务端控制台:

The time server is start in port:8080
The time server receive order : QUERY TIME ORDER

     客户端控制台:

Send order 2 server succeed.

      socketChannel.connect(new InetSocketAddress(host, port):返回false

      key.isReadable():返回false

      WHY????????????????????????????

     2.4 AIO编程

      NIO 2.0 引入了新的异步通道的概念,并提供了异步文件通道和异步套接字通道的实现。

      异步通道提供一下两种方式获取操作结果:

        通过 java.util.concurrent.Future 类来表示异步操作的结果;

        在执行异步操作的时候传入一个 java.nio.channels.CompletionHandler接口的实现类作为操作完成的回调。

      NIO 2.0 的异步套接字通道是真正的异步非阻塞I/O,对应于UNIX网络编程中的事件驱动I/O(AIO)。它不需要通过多路复用器(Selector)对注册的通道进行轮询操作即可实现异步读写,从而简化了NIO的编程模型。

      2.4.1 AIO创建的TimeServer源码分析

package com.phei.netty.aio;

public class TimeServer {

    public static void main(String[] args){
int port = 8080;
if(args != null && args.length > 0){
try{
port = Integer.valueOf(args[0]);
}catch(NumberFormatException e){
//采用默认值
}
}
// 创建异步的时间服务器处理类
AsyncTimeServerHandler timeServer = new AsyncTimeServerHandler(port);
// 启动线程
new Thread(timeServer,"AIO-AsyncTimeServerHandler-001").start();
}
}
package com.phei.netty.aio;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.channels.AsynchronousServerSocketChannel;
import java.util.concurrent.CountDownLatch; public class AsyncTimeServerHandler implements Runnable { private int port;
CountDownLatch latch;
AsynchronousServerSocketChannel asynchronousServerSocketChannel; // 创建一个异步的服务端通道AsynchronousServerSocketChannel,然后调用它的bind方法绑定监听端口。
public AsyncTimeServerHandler(int port){
this.port = port;
try{
asynchronousServerSocketChannel = AsynchronousServerSocketChannel.open();
asynchronousServerSocketChannel.bind(new InetSocketAddress(port));
System.out.println("The time server is start in port : " + port);
}catch(IOException e){
e.printStackTrace();
}
}
@Override
public void run() {
// 在完成一组正在执行的操作之前,允许当前的线程一直阻塞。
// 在本例中,我们让线程在此阻塞,防止服务端执行完成退出。
// 在实际项目应用中,不需要启动独立的线程来处理AsynchronousServerSocketChannel,这里仅仅是个demo演示
latch = new CountDownLatch(1);
// 用于接收客户端的连接,由于是异步操作,可以传递一个CompletionHandler<SsynchronousSocketChannel,? super A>类型的handler实例接收accept操作成功的通知消息
doAccept();
try{
latch.await();
}catch(InterruptedException e){
e.printStackTrace();
}
}
private void doAccept() {
asynchronousServerSocketChannel.accept(this, new AcceptCompletionHandler());
} }
package com.phei.netty.aio;

import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.CompletionHandler; public class AcceptCompletionHandler implements CompletionHandler<AsynchronousSocketChannel,AsyncTimeServerHandler> { @Override
public void completed(AsynchronousSocketChannel result, AsyncTimeServerHandler attachment) {
// 从attachment获取成员变量AsynchronousServerSocketChannel,然后继续调用她的accept方法
// 调用AsynchronousServerSocketChannel的accept方法后,
// 如果有新的客户端连接接入,系统将回调传入的CompletionHandler实例的completed方法,表示新的客户端已经接入成功。
// 因为一个AsynchronousServerSocketChannel可以接收成千上万个客户端,所以需要继续调用它的accept方法,
// 接收其他的客户端连接,最终形成一个循环。每当接收一个客户读连接成功之后,在异步连接新的客户端连接。
attachment.asynchronousServerSocketChannel.accept(attachment, this);
// 链路建立成功之后,服务端需要接收客户端的请求消息。
// 创建新的ByteBuffer,预分配1MB的缓冲区。
ByteBuffer buffer = ByteBuffer.allocate(1024);
// 通过调用AsynchronousSocketChannel的read方法进行异步读操作。
// ByteBuffer dst : 接收缓冲区,用于从异步Channel中读取数据包;
// A attachment : 异步Channel携带的附件,通知回调的时候作为入参使用;
// CompletionHandler<Integer,? super A> : 接收通知回调的业务Handler,在例程中为ReadCOmpletionHandler
result.read(buffer,buffer,new ReadCompletionHandler(result));
} @Override
public void failed(Throwable exc, AsyncTimeServerHandler attachment) {
exc.printStackTrace();
attachment.latch.countDown();
} }
package com.phei.netty.aio;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.CompletionHandler;
import java.util.Date; public class ReadCompletionHandler implements CompletionHandler<Integer, ByteBuffer> { private AsynchronousSocketChannel channel; // 将AsynchronousSocketChannel通过参数传递到ReadCompletionHandler中,
// 当作成员变量来使用,主要用于读取半包消息和发送应答
public ReadCompletionHandler(AsynchronousSocketChannel channel) {
if(this.channel == null){
this.channel = channel;
}
} // 读取到消息后的处理
@Override
public void completed(Integer result, ByteBuffer attachment) {
// 对attachment进行flip操作,为后续冲缓冲区读取数据做准备。
attachment.flip();
// 根据缓冲区的刻度字节数创建byte数组
byte[] body = new byte[attachment.remaining()];
attachment.get(body);
try{
// 通过new String方法创建请求消息,对请求消息进行判断
String req = new String(body,"UTF-8");
System.out.print("The time server receive order : " + req);
String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(req) ? new Date(System.currentTimeMillis()).toString() : "BAD ORDER";
// 调用doWrite方法发送给客户端
doWriter(currentTime);
}catch(UnsupportedEncodingException e){
e.printStackTrace();
}
} private void doWriter(String currentTime) {
// 对当前事件进行合法性校验
if(currentTime != null && currentTime.trim().length() > 0){
// 调用字符串的解码方法将应答消息编码成字节数组,然后将它复制到发送缓冲区writeBuffer中
byte[] bytes = currentTime.getBytes();
ByteBuffer writerBuffer = ByteBuffer.allocate(bytes.length);
writerBuffer.put(bytes);
writerBuffer.flip();
// 调用AsynchronousSocketChannel的异步write方法
channel.write(writerBuffer,writerBuffer,new CompletionHandler<Integer, ByteBuffer>() { @Override
public void completed(Integer result, ByteBuffer buffer) {
// 如果没有发送完成,继续发送,知道发送成功
if(buffer.hasRemaining()){
channel.write(buffer,buffer,this);
}
} @Override
public void failed(Throwable exc, ByteBuffer attachment) {
try{
channel.close();
}catch(IOException e){
//ingonre on close
}
}
});
}
} // 当发送异常的时候,对异常Throwable进行判断:如果I/O异常,就关闭链路,释放资源;
// 如果是其他异常,按照业务自己的逻辑进行处理。本例程作为简单的demo,没有对异常进行分类判断,只要发生了读写异常,就关闭链路,释放资源。
@Override
public void failed(Throwable exc, ByteBuffer attachment) {
try{
this.channel.close();
}catch(IOException e){
e.printStackTrace();
}
} }

      2.4.2 AIO创建的TimeClient源码分析

        Class :TimeClient

package com.phei.netty.aio;

public class TimeClient {

    public static void main(String[] args){
int port = 8080;
if(args != null && args.length > 0){
try{
port = Integer.valueOf(args[0]);
}catch(NumberFormatException e){ }
}
// 通过一个独立的I/O线程常见异步时间服务器客户端Handler。
// 在实际项目中,我们不需要独立的线程创建异步连接对象,因为底层都是通过JDK的系统回调实现的,
// 在后面运行时间服务器程序的时候,我们会抓取线程调用堆栈给大家展示
new Thread(new AsyncTimeClientHandler("127.0.0.1",port),"AIO-AsyncTimeClientHandler-001").start();
}
}

        Class : AsyncTimeClientHandler

package com.phei.netty.aio;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.CompletionHandler;
import java.util.concurrent.CountDownLatch; public class AsyncTimeClientHandler implements
CompletionHandler<Void, AsyncTimeClientHandler> , Runnable { private AsynchronousSocketChannel client;
private String host;
private int port;
private CountDownLatch latch; public AsyncTimeClientHandler() {
super();
} public AsyncTimeClientHandler(String host, int port) {
super();
this.host = host;
this.port = port;
try{
// 1.通过AsynchronousSocketChannel的open方法创建一个新的AsynchronousSocketChannel对象。
client = AsynchronousSocketChannel.open();
}catch(IOException e){
e.printStackTrace();
}
} public void run() {
// 2.创建CountDownLatch进行等待,防止异步操作没有执行完成线程就退出
latch = new CountDownLatch(1);
// 3.通过connect方法发起异步操作
// A attachment : AsynchronousSocketChannel 的附件,用于回调通知时作为入参被传递,调用者可自定义。
// CompletionHandler<Void,? super A> handler : 异步操作回调通知接口,由调用者实现
// 在本例程中,这两个参数都使用AsyncTimeClientHandler类本身,因为它实现了CompletionHandler接口
client.connect(new InetSocketAddress(host,port),this,this);
try{
latch.await();
}catch(InterruptedException e1){
e1.printStackTrace();
}
try{
client.close();
}catch(IOException e){
e.printStackTrace();
}
} // 4.异步连接成功之后的方法回调completed。
public void completed(Void result, AsyncTimeClientHandler attachment) {
// 创建请求消息体,对其进行编码。
byte[] req ="QUERY TIME ORDER".getBytes();
ByteBuffer writeBuffer = ByteBuffer.allocate(req.length);
// 复制到发送缓冲区writeBuffer中,
writeBuffer.put(req);
writeBuffer.flip();
// 调用AsynchronousSocketChannel的write方法进行异步写。
// 实现CompletionHandler<Integer,ByteBuffer>接口用于写操作完成后的回调
client.write(writeBuffer,writeBuffer,new CompletionHandler<Integer,ByteBuffer>(){ public void completed(Integer result, ByteBuffer buffer) {
if(buffer.hasRemaining()){
client.write(buffer,buffer,this);
}else{
ByteBuffer readBuffer = ByteBuffer.allocate(1024);
// 5.客户端异步读取时间服务器服务端应答消息的处理逻辑。
// 调用AsynchronousSocketChannel的read方法异步读取服务端的响应消息
// 由于read操作是异步的,所以我们通过内部匿名类实现CompletionHandler<Integer,ByteBuffer>接口,
// 当读取完成被JDK回调时,构造应答消息。
client.read(readBuffer,readBuffer,new CompletionHandler<Integer,ByteBuffer>(){ public void completed(Integer result,
ByteBuffer buffer) {
buffer.flip();
byte[] bytes = new byte[buffer.remaining()];
buffer.get(bytes);
String body;
try{
body = new String(bytes,"UTF-8");
System.out.println("Now is : " + body);
latch.countDown();
}catch(UnsupportedEncodingException e){
e.printStackTrace();
}
} public void failed(Throwable exc, ByteBuffer attachment) {
try{
client.close();
latch.countDown();
}catch(IOException e){
// ingnore on close
}
}
});
}
} // 当读取发生异常时,关闭链路,同时调用CountDownLatch的countDown方法让AsyncTimeClientHandler线程执行完毕,客户端退出执行
public void failed(Throwable exc, ByteBuffer attachment) {
try{
client.close();
latch.countDown();
}catch(IOException e){
//ingnore on close
}
}
});
} public void failed(Throwable exc, AsyncTimeClientHandler attachment) {
exc.printStackTrace();
try{
client.close();
latch.countDown();
}catch(IOException e){
e.printStackTrace();
}
}
}

      2.4.3 AIO版本时服务器的运行结果

    2.5 4中I/O的对比

      2.5.1 概念澄清

        1.异步非阻塞I/O

        2.多路复用器Selector

        3.伪异步I/O

      2.5.2 不同I/O模型对比

  同步阻塞I/O(BIO) 伪异步I/O 非阻塞I/O(NIO) 异步I/O(AIO)
客户端个数:I/O线程 1:1 M:N(其中M可以大于N) M:1(1个I/O线程处理多个客户端连接) M:0(不需要启动额外的I/O线程,被动回调)
I/O类型(阻塞) 阻塞I/O 阻塞I/O 非阻塞I/O 非阻塞I/O
I/O类型(同步) 同步I/O 同步I/O 同步I/O(I/O多路复用) 异步I/O
API使用难度 简单 简单 非常复杂 复杂
调试难度 简单 简单
可靠性 非常差
吞吐量

    2.6 选择Netty的理由

      2.6.1 不选择Java原生NIO编程的原因

      2.6.2 为什么选择Netty

    2.7 总结