Socket实战之六 使用NIO包实现Socket通信

本文地址：http://blog.youkuaiyun.com/kongxx/article/details/7288896
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。
[java] view plaincopyprint?
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。
[java] view plaincopyprint?
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
[java] view plaincopyprint?
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
[java] view plaincopyprint?
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