7.4 jvm之nio文件操作

NIO相比普通的IO,多的内容在于指定缓冲区和通道。这种和底层直接交互的流操作方式，相比普通流而言，在效率上有所提升。以下为完整的NIO操作实例。

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.Buffer;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class NIOOperDemo {
 public void readFileByIO(String fileName){
  FileInputStream fis=null;
  try {
    fis=new FileInputStream(fileName);
    byte[] buffer=new byte[1024];
    int len=0;
    while((len=fis.read(buffer))!=-1){
     System.out.write(buffer,0,len);
    }
  } catch (FileNotFoundException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } catch (IOException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }finally{
   try {
    fis.close();
   } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   }
  }
 }
 
 public void readByNIO(String file){
  //第一步 获取通道
  FileInputStream fis = null;
  FileChannel channel=null;
  try {
   fis = new FileInputStream(file);
   channel=fis.getChannel();
   //文件内容的大小
   int size=(int) channel.size();
   
   //第二步 指定缓冲区
      ByteBuffer buffer=ByteBuffer.allocate(1024);
   //第三步 将通道中的数据读取到缓冲区中
   channel.read(buffer);
   
   Buffer bf= buffer.flip();
   System.out.println("limt:"+bf.limit());
   
   byte[] bt=buffer.array();
   System.out.println(new String(bt,0,size));
   
   buffer.clear();
   buffer=null;
  } catch (FileNotFoundException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } catch (IOException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }finally{
   try {
    channel.close();
    fis.close();
    
   } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   }
  
   
  }
  
 }
 /**
  * 利用NIO将内容输出到文件中
  * @param file
  */
 public void writeFileByNIO(String file){
         FileOutputStream fos=null;
         FileChannel fc=null;
         ByteBuffer buffer=null;
         try {
   fos=new FileOutputStream(file);
    //第一步 获取一个通道
   fc=fos.getChannel();
   //buffer=ByteBuffer.allocate(1024);
    //第二步 定义缓冲区
   buffer=ByteBuffer.wrap("Hello World 2".getBytes());
    //将内容写到缓冲区
   fos.flush();
   fc.write(buffer);
   
  } catch (FileNotFoundException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } catch (IOException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }finally{
   try {
    fc.close();
    fos.close();
   } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   }
   
  }
 }
 public static void main(String[] args) {
  NIOOperDemo nood=new NIOOperDemo();
  String fileName="c:\\hello.txt";
  //nood.readFileByIO(fileName);
  //nood.readByNIO(fileName);
  nood.writeFileByNIO(fileName);
 }
}