JavaIO学习

参考：

Java IO:  http://www.ibm.com/developerworks/cn/java/j-lo-javaio/

Java NIO: http://www.ibm.com/developerworks/cn/education/java/j-nio/

这里写的东西为自己的总结，学习的话建议大家仔细去读上面提到的两篇文章。

Java IO分为两种：Blocking IO(BIO) & Non blocking IO(NIO)

BIO

Java中BIO包括基于字节的Stream，基于字符的Writer&Reader等，在使用时优先使用Reader&Writer。BIO经常用于与Property类一起使用读取properties文件，如下所示：

public class StreamProps {public void testStream() throws IOException{Properties props = new Properties();String path = Thread.currentThread().getContextClassLoader().getResource("").getPath().substring(1);File testFile = new File(path + "test.txt");FileReader rd = new FileReader(testFile);props.load(rd);FileWriter wt = new FileWriter(testFile);props.store(wt, "Write finished");wt.close();}public static void main(String[] args) throws IOException{Stream stream = new Stream();stream.testStream();}}

NIO

NIO的好处从名字可以看出来，可以节省资源，尤其是对于服务器，这种方式是几乎是必需的。与BIO基于流的方式不同，NIO是基于块的IO，这样对提升读取效率。NIO中这几个部分是基础：Channel，Buffer和Server端常用的Selector。

Channel：双向，用于数据传输。

Buffer：用于缓存数据

Selector：根据监听的端口来寻找注册的Channel

下面这段代码用于实现文件拷贝，使用了Channel和Buffer：

public class  NIO {private FileInputStream fin;private FileOutputStream fout;public void copyFile() throws IOException{String path = Thread.currentThread().getContextClassLoader().getResource("").getPath().substring(1);File beforeFile = new File(path + "before.txt");fin = new FileInputStream(beforeFile);File afterFile = new File(path + "after.txt");fout = new FileOutputStream(afterFile);FileChannel fcin = fin.getChannel();FileChannel fcout = fout.getChannel();ByteBuffer buffer = ByteBuffer.allocate(1024);while(true){buffer.clear();if( fcin.read(buffer) == -1 ) break;buffer.flip();fcout.write(buffer);}}public static void main(String[] args) throws IOException{NIO nio = new NIO();nio.copyFile();}}

下面这个例子介绍了Server端NIO的使用，源码来自：http://www.ibm.com/developerworks/cn/education/java/j-nio/

import java.io.*;import java.net.*;import java.nio.*;import java.nio.channels.*;import java.util.*;public class MultiPortEcho{  private int ports[];  private ByteBuffer echoBuffer = ByteBuffer.allocate( 1024 );  public MultiPortEcho( int ports[] ) throws IOException {    this.ports = ports;    go();  }  private void go() throws IOException {    // Create a new selector    Selector selector = Selector.open();    // Open a listener on each port, and register each one    // with the selector    for (int i=0; i<ports.length; ++i) {      ServerSocketChannel ssc = ServerSocketChannel.open();      ssc.configureBlocking( false );      ServerSocket ss = ssc.socket();      InetSocketAddress address = new InetSocketAddress( ports[i] );      ss.bind( address );      SelectionKey key = ssc.register( selector, SelectionKey.OP_ACCEPT );      System.out.println( "Going to listen on "+ports[i] );    }    while (true) {      int num = selector.select();      Set selectedKeys = selector.selectedKeys();      Iterator it = selectedKeys.iterator();      while (it.hasNext()) {        SelectionKey key = (SelectionKey)it.next();        if ((key.readyOps() & SelectionKey.OP_ACCEPT)          == SelectionKey.OP_ACCEPT) {          // Accept the new connection          ServerSocketChannel ssc = (ServerSocketChannel)key.channel();          SocketChannel sc = ssc.accept();          sc.configureBlocking( false );          // Add the new connection to the selector          SelectionKey newKey = sc.register( selector, SelectionKey.OP_READ );          it.remove();          System.out.println( "Got connection from "+sc );        } else if ((key.readyOps() & SelectionKey.OP_READ)          == SelectionKey.OP_READ) {          // Read the data          SocketChannel sc = (SocketChannel)key.channel();          // Echo data          int bytesEchoed = 0;          while (true) {            echoBuffer.clear();            int r = sc.read( echoBuffer );            if (r<=0) {              break;            }            echoBuffer.flip();            sc.write( echoBuffer );            bytesEchoed += r;          }          System.out.println( "Echoed "+bytesEchoed+" from "+sc );          it.remove();        }      }//System.out.println( "going to clear" );//      selectedKeys.clear();//System.out.println( "cleared" );    }  }  static public void main( String args[] ) throws Exception {    if (args.length<=0) {      System.err.println( "Usage: java MultiPortEcho port [port port ...]" );      System.exit( 1 );    }    int ports[] = new int[args.length];    for (int i=0; i<args.length; ++i) {      ports[i] = Integer.parseInt( args[i] );    }    new MultiPortEcho( ports );  }}