通过nio的Channel-Buffer来读写文件

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// 通过nio的Channel来读写文件
public class NioFileReadWrite {

 public static void main(String[] args) {
  String file = "d:\\n4.txt";
  String file2 = "d:\\ncc.txt";
  
  // 1.通过Channel-Buffer进行文件读写
//  new Thread(new ReadFileThread(file, file2)).start();
  
  // 2.内存映射文件读取: 速度快                   MappedByteBuffer
  new Thread(new MapFileReadThread(file)).start();
 }

 static class ReadFileThread implements Runnable{
  private String file;
  private String file2;
  
  public ReadFileThread(String file, String file2){
   this.file = file;
   this.file2 = file2;
  }
  
  public void run(){
   try{
    int num = 1024;
    int k =0;
    FileInputStream fis = new FileInputStream(file); 
    FileOutputStream fos = new FileOutputStream(file2);
     
          // 1.从FileInputStream对象获取文件通道FileChannel 
          FileChannel channel = fis.getChannel(); 
          FileChannel channel2 = fos.getChannel();
         
          long size = channel.size(); 
   
          // 2.从通道读取文件内容 
          byte[] bytes = new byte[num]; 
          ByteBuffer byteBuffer = ByteBuffer.allocate(num); 
   
          // 每次read都将读取 allocate 个字节到ByteBuffer 
          int len = -1; 
          while ((len = channel.read(byteBuffer)) != -1) { 
              // 注意先调用flip方法反转Buffer,再从Buffer读取数据 
              byteBuffer.flip(); 
               
              // 有几种方式可以操作ByteBuffer 
              // 1.可以将当前Buffer包含的字节数组全部读取出来 
              //bytes = byteBuffer.array(); 
              // System.out.print(new String(bytes)); 
               
              // 2.类似与InputStrean的read(byte[],offset,len)方法读取  
//              byteBuffer.get(bytes, 0, len); 
//              System.out.print(new String(bytes, 0 ,len)); 

              channel2.write(byteBuffer);
              // 最后注意调用clear方法,将Buffer的位置回归到0 
              byteBuffer.clear(); 
              k++;
          } 
         
          System.out.println("k="+k);
          // 关闭通道和文件流 
          channel.close(); 
          fis.close(); 
          channel2.close();
          fos.close();
   }catch(Exception e){
    e.printStackTrace();
   }
  }
 }
 
 static class MapFileReadThread implements Runnable{
  private String file;
  public MapFileReadThread(String file){
   this.file = file;
  }

  public void run() {
   try{
    int num = 1024;
    RandomAccessFile fis = new RandomAccessFile(new File(file), "rw"); 
          FileChannel channel = fis.getChannel(); 
          long size = channel.size(); 
           
          // 构建一个只读的MappedByteBuffer 
          MappedByteBuffer mappedByteBuffer = channel.map(MapMode.READ_ONLY, 0, size); 
           
          // 如果文件不大,可以选择一次性读取到数组 
          // byte[] all = new byte[(int)size]; 
          // mappedByteBuffer.get(all, 0, (int)size); 
           
          // 如果文件内容很大,可以循环读取,计算应该读取多少次 
          byte[] bytes = new byte[num]; 
          long cycle = size / num; 
          int mode = (int)(size % num); 
          for (int i = 0; i < cycle; i++) { 
              // 每次读取allocate个字节 
              mappedByteBuffer.get(bytes); 
               
              // 打印文件内容,关闭打印速度会很快 
               System.out.print(new String(bytes)); 
          } 
          if(mode > 0) { 
              bytes = new byte[mode]; 
              mappedByteBuffer.get(bytes); 
              System.out.print(new String(bytes));
          } 
   
          // 关闭通道和文件流 
          channel.close(); 
          fis.close();
   }catch(Exception e){
    e.printStackTrace();
   }
  }
  
 }
}