前面几篇文章介绍了使用java.io和java.net类库实现的Socket通信，下面介绍一下使用java.nio类库实现的Socket。

java.nio包是Java在1.4之后增加的，用来提高I/O操作的效率。在nio包中主要包括以下几个类或接口:

* Buffer：缓冲区，用来临时存放输入或输出数据。

* Charset：用来把Unicode字符编码和其它字符编码互转。

* Channel：数据传输通道，用来把Buffer中的数据写入到数据源，或者把数据源中的数据读入到Buffer。

* Selector：用来支持异步I/O操作，也叫非阻塞I/O操作。

nio包中主要通过下面两个方面来提高I/O操作效率:

* 通过Buffer和Channel来提高I/O操作的速度。

* 通过Selector来支持非阻塞I/O操作。

下面来看一下程序中是怎么通过这些类库实现Socket功能。

首先介绍一下几个辅助类

辅助类SerializableUtil，这个类用来把java对象序列化成字节数组，或者把字节数组反序列化成java对象。

package com.googlecode.garbagecan.test.socket;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class SerializableUtil {
	
	public static byte[] toBytes(Object object) {
		ByteArrayOutputStream baos = new ByteArrayOutputStream();
		ObjectOutputStream oos = null;
		try {
			oos = new ObjectOutputStream(baos);
			oos.writeObject(object);
			byte[] bytes = baos.toByteArray();
			return bytes;
		} catch(IOException ex) {
			throw new RuntimeException(ex.getMessage(), ex);
		} finally {
			try {
				oos.close();
			} catch (Exception e) {}
		}
	}
	
	public static Object toObject(byte[] bytes) {
		ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
		ObjectInputStream ois = null;
		try {
			ois = new ObjectInputStream(bais);
			Object object = ois.readObject();
			return object;
		} catch(IOException ex) {
			throw new RuntimeException(ex.getMessage(), ex);
		} catch(ClassNotFoundException ex) {
			throw new RuntimeException(ex.getMessage(), ex);
		} finally {
			try {
				ois.close();
			} catch (Exception e) {}
		}
	}
}

辅助类MyRequestObject和MyResponseObject，这两个类是普通的java对象，实现了Serializable接口。MyRequestObject类是Client发出的请求，MyResponseObject是Server端作出的响应。

package com.googlecode.garbagecan.test.socket.nio;

import java.io.Serializable;

public class MyRequestObject implements Serializable {

	private static final long serialVersionUID = 1L;

	private String name;
	
	private String value;

	private byte[] bytes;
	
	public MyRequestObject(String name, String value) {
		this.name = name;
		this.value = value;
		this.bytes = new byte[1024];
	}
	
	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getValue() {
		return value;
	}

	public void setValue(String value) {
		this.value = value;
	}
	
	@Override
	public String toString() {
		StringBuffer sb = new StringBuffer();
		sb.append("Request [name: " + name  + ", value: " + value + ", bytes: " + bytes.length+ "]");
		return sb.toString();
	}
}

package com.googlecode.garbagecan.test.socket.nio;

import java.io.Serializable;

public class MyResponseObject implements Serializable {

	private static final long serialVersionUID = 1L;

	private String name;
	
	private String value;

	private byte[] bytes;
	
	public MyResponseObject(String name, String value) {
		this.name = name;
		this.value = value;
		this.bytes = new byte[1024];
	}
	
	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getValue() {
		return value;
	}

	public void setValue(String value) {
		this.value = value;
	}
	
	@Override
	public String toString() {
		StringBuffer sb = new StringBuffer();
		sb.append("Response [name: " + name  + ", value: " + value + ", bytes: " + bytes.length+ "]");
		return sb.toString();
	}
}

下面主要看一下Server端的代码，其中有一些英文注释对理解代码很有帮助，注释主要是来源jdk的文档和例子，这里就没有再翻译

package com.googlecode.garbagecan.test.socket.nio;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.ClosedChannelException;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.logging.Level;
import java.util.logging.Logger;

import com.googlecode.garbagecan.test.socket.SerializableUtil;

public class MyServer3 {

	private final static Logger logger = Logger.getLogger(MyServer3.class.getName());
	
	public static void main(String[] args) {
		Selector selector = null;
		ServerSocketChannel serverSocketChannel = null;
		
		try {
			// Selector for incoming time requests
			selector = Selector.open();

			// Create a new server socket and set to non blocking mode
			serverSocketChannel = ServerSocketChannel.open();
			serverSocketChannel.configureBlocking(false);
			
			// Bind the server socket to the local host and port
			serverSocketChannel.socket().setReuseAddress(true);
			serverSocketChannel.socket().bind(new InetSocketAddress(10000));
			
			// Register accepts on the server socket with the selector. This
			// step tells the selector that the socket wants to be put on the
			// ready list when accept operations occur, so allowing multiplexed
			// non-blocking I/O to take place.
			serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
	
			// Here's where everything happens. The select method will
			// return when any operations registered above have occurred, the
			// thread has been interrupted, etc.
			while (selector.select() > 0) {
				// Someone is ready for I/O, get the ready keys
				Iterator<SelectionKey> it = selector.selectedKeys().iterator();
	
				// Walk through the ready keys collection and process date requests.
				while (it.hasNext()) {
					SelectionKey readyKey = it.next();
					it.remove();
					
					// The key indexes into the selector so you
					// can retrieve the socket that's ready for I/O
					execute((ServerSocketChannel) readyKey.channel());
				}
			}
		} catch (ClosedChannelException ex) {
			logger.log(Level.SEVERE, null, ex);
		} catch (IOException ex) {
			logger.log(Level.SEVERE, null, ex);
		} finally {
			try {
				selector.close();
			} catch(Exception ex) {}
			try {
				serverSocketChannel.close();
			} catch(Exception ex) {}
		}
	}

	private static void execute(ServerSocketChannel serverSocketChannel) throws IOException {
		SocketChannel socketChannel = null;
		try {
			socketChannel = serverSocketChannel.accept();
			MyRequestObject myRequestObject = receiveData(socketChannel);
			logger.log(Level.INFO, myRequestObject.toString());
			
			MyResponseObject myResponseObject = new MyResponseObject(
					"response for " + myRequestObject.getName(), 
					"response for " + myRequestObject.getValue());
			sendData(socketChannel, myResponseObject);
			logger.log(Level.INFO, myResponseObject.toString());
		} finally {
			try {
				socketChannel.close();
			} catch(Exception ex) {}
		}
	}
	
	private static MyRequestObject receiveData(SocketChannel socketChannel) throws IOException {
		MyRequestObject myRequestObject = null;
		ByteArrayOutputStream baos = new ByteArrayOutputStream();
		ByteBuffer buffer = ByteBuffer.allocate(1024);
		
		try {
			byte[] bytes;
			int size = 0;
			while ((size = socketChannel.read(buffer)) >= 0) {
				buffer.flip();
				bytes = new byte[size];
				buffer.get(bytes);
				baos.write(bytes);
				buffer.clear();
			}
			bytes = baos.toByteArray();
			Object obj = SerializableUtil.toObject(bytes);
			myRequestObject = (MyRequestObject)obj;
		} finally {
			try {
				baos.close();
			} catch(Exception ex) {}
		}
		return myRequestObject;
	}

	private static void sendData(SocketChannel socketChannel, MyResponseObject myResponseObject) throws IOException {
		byte[] bytes = SerializableUtil.toBytes(myResponseObject);
		ByteBuffer buffer = ByteBuffer.wrap(bytes);
		socketChannel.write(buffer);
	}
}

下面是Client的代码，代码比较简单就是启动了100个线程来访问Server

package com.googlecode.garbagecan.test.socket.nio;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SocketChannel;
import java.util.logging.Level;
import java.util.logging.Logger;

import com.googlecode.garbagecan.test.socket.SerializableUtil;

public class MyClient3 {

	private final static Logger logger = Logger.getLogger(MyClient3.class.getName());
	
	public static void main(String[] args) throws Exception {
		for (int i = 0; i < 100; i++) {
			final int idx = i;
			new Thread(new MyRunnable(idx)).start();
		}
	}
	
	private static final class MyRunnable implements Runnable {
		
		private final int idx;

		private MyRunnable(int idx) {
			this.idx = idx;
		}

		public void run() {
			SocketChannel socketChannel = null;
			try {
				socketChannel = SocketChannel.open();
				SocketAddress socketAddress = new InetSocketAddress("localhost", 10000);
				socketChannel.connect(socketAddress);

				MyRequestObject myRequestObject = new MyRequestObject("request_" + idx, "request_" + idx);
				logger.log(Level.INFO, myRequestObject.toString());
				sendData(socketChannel, myRequestObject);
				
				MyResponseObject myResponseObject = receiveData(socketChannel);
				logger.log(Level.INFO, myResponseObject.toString());
			} catch (Exception ex) {
				logger.log(Level.SEVERE, null, ex);
			} finally {
				try {
					socketChannel.close();
				} catch(Exception ex) {}
			}
		}

		private void sendData(SocketChannel socketChannel, MyRequestObject myRequestObject) throws IOException {
			byte[] bytes = SerializableUtil.toBytes(myRequestObject);
			ByteBuffer buffer = ByteBuffer.wrap(bytes);
			socketChannel.write(buffer);
			socketChannel.socket().shutdownOutput();
		}

		private MyResponseObject receiveData(SocketChannel socketChannel) throws IOException {
			MyResponseObject myResponseObject = null;
			ByteArrayOutputStream baos = new ByteArrayOutputStream();
			
			try {
				ByteBuffer buffer = ByteBuffer.allocateDirect(1024);
				byte[] bytes;
				int count = 0;
				while ((count = socketChannel.read(buffer)) >= 0) {
					buffer.flip();
					bytes = new byte[count];
					buffer.get(bytes);
					baos.write(bytes);
					buffer.clear();
				}
				bytes = baos.toByteArray();
				Object obj = SerializableUtil.toObject(bytes);
				myResponseObject = (MyResponseObject) obj;
				socketChannel.socket().shutdownInput();
			} finally {
				try {
					baos.close();
				} catch(Exception ex) {}
			}
			return myResponseObject;
		}
	}
}

最后测试上面的代码，首先运行Server类，然后运行Client类，就可以分别在Server端和Client端控制台看到发送或接收到的MyRequestObject或MyResponseObject对象了。

关于NIO和IO的比较，下面的两篇文章对理解很有帮助，可以参考一下。

http://tutorials.jenkov.com/java-nio/nio-vs-io.html

https://blogs.oracle.com/slc/entry/javanio_vs_javaio

posted @ 2012-02-23 22:32 程序员天下阅读(378) 评论(0) 编辑收藏举报

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