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。
简单的说，NIO1.0 和NIO2.0 相比最大的区别是NIO1.0通过多路复用器轮询来获取读写事件，然后执行具体的操作，NIO2.0采用和Future和回调，使用上更加简洁。
下面是一个例子，客户端向服务端发一个时间查询消息，服务端返回查询的结果。
eg
服务端：
public class TimeServer {
public static void main(String[] args) {
AsyncTimeServerHandler asyncTimeServerHandler=new AsyncTimeServerHandler(8080);
new Thread(asyncTimeServerHandler,"AI0-SERVER").start();
}
}public class AsyncTimeServerHandler implements Runnable {
private int port;
CountDownLatch latch;
AsynchronousServerSocketChannel asynchronousServerSocketChannel;
AsyncTimeServerHandler(int port) {
this.port = port;
try {
//创建一个服务端通道
asynchronousServerSocketChannel = AsynchronousServerSocketChannel.open();
//绑定监听端口
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() {
latch = new CountDownLatch(1);
//接收客户端请求
doAccept();
try {
latch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public void doAccept() {
//注册接收客户端请求，接收到请求会回调acceptCompletionHandler类
asynchronousServerSocketChannel.accept(this, new AcceptCompletionHandler());
}
}public class AcceptCompletionHandler implements CompletionHandler<AsynchronousSocketChannel, AsyncTimeServerHandler> {
@Override
public void completed(AsynchronousSocketChannel result, AsyncTimeServerHandler attachment) {
//接收到客户端请求后，在注册接收请求，用于接收其他客户端的请求
attachment.asynchronousServerSocketChannel.accept(attachment, this);
ByteBuffer buffer = ByteBuffer.allocate(1024);
//监听该客户端连接上的读请求，如果接收到消息，会调用readCompletionHandler
result.read(buffer, buffer, new ReadCompletionHandler(result));
}
@Override
public void failed(Throwable exc, AsyncTimeServerHandler attachment) {
//接收失败的回调
exc.printStackTrace();
attachment.latch.countDown();
}
}public class ReadCompletionHandler implements CompletionHandler<Integer,ByteBuffer>{
private AsynchronousSocketChannel channel;
public ReadCompletionHandler(AsynchronousSocketChannel channel){
this.channel=channel;
}
@Override
public void completed(Integer result, ByteBuffer attachment) {
//读取客户端请求
attachment.flip();
byte[] body=new byte[attachment.remaining()];
attachment.get(body);
try {
String req=new String(body,"UTF-8");
System.out.println("The time server receive order:"+req);
String currentTime="QUERY TIME ORDER".equalsIgnoreCase(req)?
new Date(System.currentTimeMillis()).toString():"BAD ORDER";
//回复客户端消息
doWrite(currentTime);
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
}
@Override
public void failed(Throwable exc, ByteBuffer attachment) {
try {
this.channel.close();
} catch (IOException e) {
e.printStackTrace();
}
}
private void doWrite(String currentTime){
if(currentTime!=null&¤tTime.trim().length()>0){
byte[] bytes=currentTime.getBytes();
ByteBuffer writeBuffer=ByteBuffer.allocate(bytes.length);
writeBuffer.put(bytes);
writeBuffer.flip();
//向客户端回复消息
channel.write(writeBuffer, writeBuffer,
new CompletionHandler<Integer, ByteBuffer>() {
@Override
public void completed(Integer result, ByteBuffer attachment) {
// 如果没有发送完成，继续发送
if(attachment.hasRemaining()){
channel.write(attachment,attachment,this);
}
}
@Override
public void failed(Throwable exc, ByteBuffer attachment) {
try {
channel.close();
} catch (IOException e) {
e.printStackTrace();
}
}
});
}
}
}客户端:
public class TimeClient {
public static void main(String[] args) {
AsyncTimeClientHandler asyncTimeClientHandler = new AsyncTimeClientHandler("127.0.0.1", 8080);
new Thread(asyncTimeClientHandler, "client-1").start();
}
}public class AsyncTimeClientHandler implements CompletionHandler<Void, AsyncTimeClientHandler>, Runnable {
private AsynchronousSocketChannel client;
private String host;
private int port;
private CountDownLatch latch;
public AsyncTimeClientHandler(String host, int port) {
this.host = host;
this.port = port;
try {
//创建一个连接通道
client = AsynchronousSocketChannel.open();
} catch (IOException e) {
e.printStackTrace();
}
}
@Override
public void run() {
latch = new CountDownLatch(1);
//异步连接服务端，连接成功回调this
client.connect(new InetSocketAddress(host, port), this, this);
try {
latch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
try {
client.close();
} catch (IOException e) {
e.printStackTrace();
}
}
@Override
public void completed(Void result, AsyncTimeClientHandler attachment) {
//连接成功发送消息
byte[] req = "QUERY TIME ORDER".getBytes();
ByteBuffer writeBuffer = ByteBuffer.allocate(req.length);
writeBuffer.put(req);
writeBuffer.flip();
client.write(writeBuffer, writeBuffer,
new CompletionHandler<Integer, ByteBuffer>() {
@Override
public void completed(Integer result, ByteBuffer attachment) {
if (attachment.hasRemaining()) {
client.write(attachment, attachment, this);
} else {
ByteBuffer readBuffer = ByteBuffer.allocate(1024);
//发送完消息，监听读消息
client.read(
readBuffer,
readBuffer,
new CompletionHandler<Integer, ByteBuffer>() {
@Override
public void completed(Integer result, ByteBuffer attachment) {
attachment.flip();
byte[] bytes = new byte[attachment.remaining()];
attachment.get(bytes);
String body;
try {
body = new String(bytes, "UTF-8");
System.out.println("Now is :" + body);
latch.countDown();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
}
@Override
public void failed(Throwable exc, ByteBuffer attachment) {
try {
client.close();
latch.countDown();
} catch (IOException e) {
e.printStackTrace();
}
}
}
);
}
}
@Override
public void failed(Throwable exc, ByteBuffer attachment) {
try {
client.close();
latch.countDown();
} catch (IOException e) {
e.printStackTrace();
}
}
});
}
@Override
public void failed(Throwable exc, AsyncTimeClientHandler attachment) {
try {
client.close();
latch.countDown();
} catch (IOException e) {
e.printStackTrace();
}
}
}
