转：Java NIO（2）

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。