AIO用于文件处理还是比较快乐的，但用AIO来写网络消息处理服务器端与客户端是比较麻烦的事情，当然这只是我个人意见，主要是有几点原因：
一是AIO需要操作系统支持，还好Windows与Linux(模拟)都支持；
二是AIO同时使用递归调用和异步调用容易把程序员搞晕，代码容易出错；
三是CompletionHandler会使用单独的线程跑，容易出现多线程问题，频繁线程上下文切换比较消耗资源；
四是异步写要创建队列来缓存需要写入的数据，否则肯定会遇到WritePendingException。
相对来说，NIO比较清楚直白，容易控制。
另外，笔者使用多线程模拟多个客户场景失败，代码在run方法中调用AsynchronousSocketChannel.connect()没返回，没连接上服务器，不知道为何，请大侠指教，最后只好使用多个进程模拟多个客户端，写个类似下面代码的bat文件，同时运行多个。
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服务器代码：
package aio;
/**
* Created by Administrator on 2016/10/28.
*/
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.StandardSocketOptions;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.AsynchronousChannelGroup;
import java.nio.channels.AsynchronousServerSocketChannel;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.CompletionHandler;
//import java.nio.channels.WritePendingException;
import java.nio.charset.CharacterCodingException;
import java.nio.charset.Charset;
import java.util.LinkedList;
import java.util.Queue;
import java.util.concurrent.Executors;
public class XiaoNa {
private final AsynchronousServerSocketChannel server;
//写队列，因为当前一个异步写调用还没完成之前，调用异步写会抛WritePendingException
//所以需要一个写队列来缓存要写入的数据，这是AIO比较坑的地方
private final Queue<ByteBuffer> queue = new LinkedList<ByteBuffer>();
private boolean writing = false;
public static void main(String[] args) throws IOException{
XiaoNa xiaona = new XiaoNa();
xiaona.listen();
}
public XiaoNa() throws IOException{
//设置线程数为CPU核数
AsynchronousChannelGroup channelGroup = AsynchronousChannelGroup.withFixedThreadPool(Runtime.getRuntime().availableProcessors(), Executors.defaultThreadFactory());
server = AsynchronousServerSocketChannel.open(channelGroup);
//重用端口
server.setOption(StandardSocketOptions.SO_REUSEADDR, true);
//绑定端口并设置连接请求队列长度
server.bind(new InetSocketAddress(8383), 80);
}
public void listen() {
System.out.println(Thread.currentThread().getName() + ": run in listen method" );
//开始接受第一个连接请求
server.accept(null, new CompletionHandler<AsynchronousSocketChannel, Object>(){
@Override
public void completed(AsynchronousSocketChannel channel,
Object attachment) {
System.out.println(Thread.currentThread().getName() + ": run in accept completed method" );
//先安排处理下一个连接请求，异步非阻塞调用，所以不用担心挂住了
//这里传入this是个地雷，小心多线程
server.accept(null, this);
//处理连接读写
handle(channel);
}
private void handle(final AsynchronousSocketChannel channel) {
System.out.println(Thread.currentThread().getName() + ": run in handle method" );
//每个AsynchronousSocketChannel，分配一个缓冲区
final ByteBuffer readBuffer = ByteBuffer.allocateDirect(1024);
readBuffer.clear();
channel.read(readBuffer, null, new CompletionHandler<Integer, Object>(){
@Override
public void completed(Integer count, Object attachment) {
System.out.println(Thread.currentThread().getName() + ": run in read completed method" );
if(count > 0){
try{
readBuffer.flip();
//CharBuffer charBuffer = CharsetHelper.decode(readBuffer);
CharBuffer charBuffer = Charset.forName("UTF-8").newDecoder().decode(readBuffer);
String question = charBuffer.toString();
String answer = Helper.getAnswer(question);
/*//写入也是异步调用，也可以使用传入CompletionHandler对象的方式来处理写入结果
//channel.write(CharsetHelper.encode(CharBuffer.wrap(answer)));
try{
channel.write(Charset.forName("UTF-8").newEncoder().encode(CharBuffer.wrap(answer)));
}
//Unchecked exception thrown when an attempt is made to write to an asynchronous socket channel and a previous write has not completed.
//看来操作系统也不可靠
catch(WritePendingException wpe){
//休息一秒再重试，如果失败就不管了
Helper.sleep(1);
channel.write(Charset.forName("UTF-8").newEncoder().encode(CharBuffer.wrap(answer)));
}*/
writeStringMessage(channel, answer);
readBuffer.clear();
}
catch(IOException e){
e.printStackTrace();
}
}
else{
try {
//如果客户端关闭socket，那么服务器也需要关闭，否则浪费CPU
channel.close();
} catch (IOException e) {
e.printStackTrace();
}
}
//异步调用OS处理下个读取请求
//这里传入this是个地雷，小心多线程
channel.read(readBuffer, null, this);
}
/**
* 服务器读失败处理
* @param exc
* @param attachment
*/
@Override
public void failed(Throwable exc, Object attachment) {
System.out.println("server read failed: " + exc);
if(channel != null){
try {
channel.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
});
}
/**
* 服务器接受连接失败处理
* @param exc
* @param attachment
*/
@Override
public void failed(Throwable exc, Object attachment) {
System.out.println("server accept failed: " + exc);
}
});
}
/**
* Enqueues a write of the buffer to the channel.
* The call is asynchronous so the buffer is not safe to modify after
* passing the buffer here.
*
* @param buffer the buffer to send to the channel
*/
private void writeMessage(final AsynchronousSocketChannel channel, final ByteBuffer buffer) {
boolean threadShouldWrite = false;
synchronized(queue) {
queue.add(buffer);
// Currently no thread writing, make this thread dispatch a write
if (!writing) {
writing = true;
threadShouldWrite = true;
}
}
if (threadShouldWrite) {
writeFromQueue(channel);
}
}
private void writeFromQueue(final AsynchronousSocketChannel channel) {
ByteBuffer buffer;
synchronized (queue) {
buffer = queue.poll();
if (buffer == null) {
writing = false;
}
}
// No new data in buffer to write
if (writing) {
writeBuffer(channel, buffer);
}
}
private void writeBuffer(final AsynchronousSocketChannel channel, ByteBuffer buffer) {
channel.write(buffer, buffer, new CompletionHandler<Integer, ByteBuffer>() {
@Override
public void completed(Integer result, ByteBuffer buffer) {
if (buffer.hasRemaining()) {
channel.write(buffer, buffer, this);
} else {
// Go back and check if there is new data to write
writeFromQueue(channel);
}
}
@Override
public void failed(Throwable exc, ByteBuffer attachment) {
System.out.println("server write failed: " + exc);
}
});
}
/**
* Sends a message
* @param msg
* @throws CharacterCodingException
*/
private void writeStringMessage(final AsynchronousSocketChannel channel, String msg) throws CharacterCodingException {
writeMessage(channel, Charset.forName("UTF-8").newEncoder().encode(CharBuffer.wrap(msg)));
}
}客户端代码：
package aio;
/**
* Created by Administrator on 2016/10/28.
*/
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.StandardSocketOptions;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.AsynchronousChannelGroup;
import java.nio.channels.AsynchronousSocketChannel;
import java.nio.channels.CompletionHandler;
import java.nio.charset.CharacterCodingException;
import java.nio.charset.Charset;
import java.util.LinkedList;
import java.util.Queue;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Executors;
public class Client implements Runnable{
private AsynchronousSocketChannel channel;
private Helper helper;
private CountDownLatch latch;
private final Queue<ByteBuffer> queue = new LinkedList<ByteBuffer>();
private boolean writing = false;
public Client(AsynchronousChannelGroup channelGroup, CountDownLatch latch) throws IOException, InterruptedException{
this.latch = latch;
helper = new Helper();
initChannel(channelGroup);
}
private void initChannel(AsynchronousChannelGroup channelGroup) throws IOException {
//在默认channel group下创建一个socket channel
channel = AsynchronousSocketChannel.open(channelGroup);
//设置Socket选项
channel.setOption(StandardSocketOptions.TCP_NODELAY, true);
channel.setOption(StandardSocketOptions.SO_KEEPALIVE, true);
channel.setOption(StandardSocketOptions.SO_REUSEADDR, true);
}
public static void main(String[] args) throws IOException, InterruptedException {
int sleepTime = Integer.parseInt(args[0]);
Helper.sleep(sleepTime);
AsynchronousChannelGroup channelGroup = AsynchronousChannelGroup.withFixedThreadPool(Runtime.getRuntime().availableProcessors(), Executors.defaultThreadFactory());
//只能跑一个线程，第二个线程connect会挂住，暂时不明原因
final int THREAD_NUM = 1;
CountDownLatch latch = new CountDownLatch(THREAD_NUM);
//创建个多线程模拟多个客户端，模拟失败，无效
//只能通过命令行同时运行多个进程来模拟多个客户端
for(int i=0; i<THREAD_NUM; i++){
Client c = new Client(channelGroup, latch);
Thread t = new Thread(c);
System.out.println(t.getName() + "---start");
t.start();
//让主线程等待子线程处理再退出, 这对于异步调用无效
//t.join();
}
latch.await();
if(channelGroup !=null){
channelGroup.shutdown();
}
}
@Override
public void run() {
System.out.println(Thread.currentThread().getName() + "---run");
//连接服务器
channel.connect(new InetSocketAddress("localhost", 8383), null, new CompletionHandler<Void, Void>(){
final ByteBuffer readBuffer = ByteBuffer.allocateDirect(1024);
@Override
public void completed(Void result, Void attachment) {
//连接成功后, 异步调用OS向服务器写一条消息
try {
//channel.write(CharsetHelper.encode(CharBuffer.wrap(helper.getWord())));
writeStringMessage(helper.getWord());
} catch (CharacterCodingException e) {
e.printStackTrace();
}
//helper.sleep();//等待写异步调用完成
readBuffer.clear();
//异步调用OS读取服务器发送的消息
channel.read(readBuffer, null, new CompletionHandler<Integer, Object>(){
@Override
public void completed(Integer result, Object attachment) {
try{
//异步读取完成后处理
if(result > 0){
readBuffer.flip();
CharBuffer charBuffer = CharsetHelper.decode(readBuffer);
String answer = charBuffer.toString();
System.out.println(Thread.currentThread().getName() + "---" + answer);
readBuffer.clear();
String word = helper.getWord();
if(word != null){
//异步写
//channel.write(CharsetHelper.encode(CharBuffer.wrap(word)));
writeStringMessage(word);
//helper.sleep();//等待异步操作
channel.read(readBuffer, null, this);
}
else{
//不想发消息了，主动关闭channel
shutdown();
}
}
else{
//对方已经关闭channel，自己被动关闭，避免空循环
shutdown();
}
}
catch(Exception e){
e.printStackTrace();
}
}
/**
* 读取失败处理
* @param exc
* @param attachment
*/
@Override
public void failed(Throwable exc, Object attachment) {
System.out.println("client read failed: " + exc);
try {
shutdown();
} catch (IOException e) {
e.printStackTrace();
}
}
});
}
/**
* 连接失败处理
* @param exc
* @param attachment
*/
@Override
public void failed(Throwable exc, Void attachment) {
System.out.println("client connect to server failed: " + exc);
try {
shutdown();
} catch (IOException e) {
e.printStackTrace();
}
}
});
}
private void shutdown() throws IOException {
if(channel != null){
channel.close();
}
latch.countDown();
}
/**
* Enqueues a write of the buffer to the channel.
* The call is asynchronous so the buffer is not safe to modify after
* passing the buffer here.
*
* @param buffer the buffer to send to the channel
*/
private void writeMessage(final ByteBuffer buffer) {
boolean threadShouldWrite = false;
synchronized(queue) {
queue.add(buffer);
// Currently no thread writing, make this thread dispatch a write
if (!writing) {
writing = true;
threadShouldWrite = true;
}
}
if (threadShouldWrite) {
writeFromQueue();
}
}
private void writeFromQueue() {
ByteBuffer buffer;
synchronized (queue) {
buffer = queue.poll();
if (buffer == null) {
writing = false;
}
}
// No new data in buffer to write
if (writing) {
writeBuffer(buffer);
}
}
private void writeBuffer(ByteBuffer buffer) {
channel.write(buffer, buffer, new CompletionHandler<Integer, ByteBuffer>() {
@Override
public void completed(Integer result, ByteBuffer buffer) {
if (buffer.hasRemaining()) {
channel.write(buffer, buffer, this);
} else {
// Go back and check if there is new data to write
writeFromQueue();
}
}
@Override
public void failed(Throwable exc, ByteBuffer attachment) {
}
});
}
/**
* Sends a message
* @param msg
* @throws CharacterCodingException
*/
public void writeStringMessage(String msg) throws CharacterCodingException {
writeMessage(Charset.forName("UTF-8").newEncoder().encode(CharBuffer.wrap(msg)));
}
} 工具类：
package aio;
/**
* Created by Administrator on 2016/10/28.
*/
import java.util.Random;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;
public class Helper {
private static BlockingQueue<String> words;
private static Random random;
public Helper() throws InterruptedException{
words = new ArrayBlockingQueue<String>(5);
words.put("hi");
words.put("who");
words.put("what");
words.put("where");
words.put("bye");
random = new Random();
}
public String getWord(){
return words.poll();
}
public void sleep() {
try {
TimeUnit.SECONDS.sleep(random.nextInt(3));
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public static void sleep(long l) {
try {
TimeUnit.SECONDS.sleep(l);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public static String getAnswer(String question){
String answer = null;
switch(question){
case "who":
answer = "我是小娜\n";
break;
case "what":
answer = "我是来帮你解闷的\n";
break;
case "where":
answer = "我来自外太空\n";
break;
case "hi":
answer = "hello\n";
break;
case "bye":
answer = "88\n";
break;
default:
answer = "请输入 who， 或者what， 或者where";
}
return answer;
}
}
package aio;
/**
* Created by Administrator on 2016/10/28.
*/
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.CharacterCodingException;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CharsetEncoder;
public class CharsetHelper {
private static final String UTF_8 = "UTF-8";
private static CharsetEncoder encoder = Charset.forName(UTF_8).newEncoder();
private static CharsetDecoder decoder = Charset.forName(UTF_8).newDecoder();
public static ByteBuffer encode(CharBuffer in) throws CharacterCodingException{
return encoder.encode(in);
}
public static CharBuffer decode(ByteBuffer in) throws CharacterCodingException{
return decoder.decode(in);
}
}
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