转：Java NIO（2）

Z时代
2024-01-10
分类：综合

java

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 plain copy

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。

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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 plain copy

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 plain copy

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。

以上是转：Java NIO（2）的全部内容，来源链接： utcz.com/z/394826.html

转：Java NIO（2）

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