Java实现文件拷贝的4种方法

使用 java 进行文件拷贝 相信很多人都会用,不过效率上是否最好呢?最近看了看NIO决定试一试 java  NIO 到底有什么性能的提升.

第一种方法:古老的方式

  public   static   long  forJava(File f1,File f2)  throws  Exception{
   long  time = new  Date().getTime();
   int  length = 2097152 ;
  FileInputStream in = new  FileInputStream(f1);
  FileOutputStream out = new  FileOutputStream(f2);
   byte [] buffer = new   byte [length];
   while ( true ){
    int  ins = in.read(buffer);
    if (ins ==- 1 ){
    in.close();
    out.flush();
    out.close();
     return   new  Date().getTime() - time;
   } else
    out.write(buffer, 0 ,ins);
  }
 }

方法的2参数分别是原始文件,和拷贝的目的文件.这里不做过多介绍.

实现方法很简单,分别对2个文件构建输入输出流,并且使用一个字节数组作为我们内存的缓存器, 然后使用流从f1 中读出数据到缓存里,在将缓存数据写到f2里面去.这里的缓存是2MB的字节数组

第2种方法:使用NIO中的管道到管道传输

     public   static   long  forTransfer(File f1,File f2)  throws  Exception{
         long  time = new  Date().getTime();
         int  length = 2097152 ;
        FileInputStream in = new  FileInputStream(f1);
        FileOutputStream out = new  FileOutputStream(f2);
        FileChannel inC = in.getChannel();
        FileChannel outC = out.getChannel();
         int  i = 0 ;
         while ( true ){
             if (inC.position() == inC.size()){
                inC.close();
                outC.close();
                 return   new  Date().getTime() - time;
            }
             if ((inC.size() - inC.position()) < 20971520 )
                length = ( int )(inC.size() - inC.position());
             else
                length = 20971520 ;
            inC.transferTo(inC.position(),length,outC);
            inC.position(inC.position() + length);
            i ++ ;
        }
    }

实现方法:在第一种实现方法基础上对输入输出流获得其管道,然后分批次的从f1的管道中像f2的管道中输入数据每次输入的数据最大为2MB

方法3:内存文件景象写(读文件没有使用文件景象,有兴趣的可以回去试试,,我就不试了,估计会更快)

     public   static   long  forImage(File f1,File f2)  throws  Exception{
         long  time = new  Date().getTime();
         int  length = 2097152 ;
        FileInputStream in = new  FileInputStream(f1);
        RandomAccessFile out = new  RandomAccessFile(f2, " rw " );
        FileChannel inC = in.getChannel();
        MappedByteBuffer outC = null ;
        MappedByteBuffer inbuffer = null ;
         byte [] b = new   byte [length];
         while ( true ){
             if (inC.position() == inC.size()){
                inC.close();
                outC.force();
                out.close();
                 return   new  Date().getTime() - time;
            }
             if ((inC.size() - inC.position()) < length){
                length = ( int )(inC.size() - inC.position());
            } else {
                length = 20971520 ;
            }
            b = new   byte [length];
            inbuffer = inC.map(MapMode.READ_ONLY,inC.position(),length);
            inbuffer.load();
            inbuffer.get(b);
            outC = out.getChannel().map(MapMode.READ_WRITE,inC.position(),length);
            inC.position(b.length + inC.position());
            outC.put(b);
            outC.force();
        }
    }

实现方法:跟伤2个例子不一样,这里写文件流没有使用管道而是使用内存文件映射(假设文件f2在内存中).在循环中从f1的管道中读取数据到字节数组里,然后在像内存映射的f2文件中写数据.

第4种方法:管道对管道

     public   static   long  forChannel(File f1,File f2)  throws  Exception{
         long  time = new  Date().getTime();
         int  length = 2097152 ;
        FileInputStream in = new  FileInputStream(f1);
        FileOutputStream out = new  FileOutputStream(f2);
        FileChannel inC = in.getChannel();
        FileChannel outC = out.getChannel();
        ByteBuffer b = null ;
         while ( true ){
             if (inC.position() == inC.size()){
                inC.close();
                outC.close();
                 return   new  Date().getTime() - time;
            }
             if ((inC.size() - inC.position()) < length){
                length = ( int )(inC.size() - inC.position());
            } else
                length = 2097152 ;
            b = ByteBuffer.allocateDirect(length);
            inC.read(b);
            b.flip();
            outC.write(b);
            outC.force( false );
        }
    }

这里实现方式与第3种实现方式很类似,不过没有使用内存影射.

 

下面是对49.3MB的文件进行拷贝的测试时间(毫秒)

Start Copy File...  file size:50290KB
CopyFile:b1.rmvb mode:forChannel  RunTime:3203
CopyFile:b1.rmvb mode:forImage  RunTime:3328
CopyFile:b1.rmvb mode:forJava  RunTime:2172
CopyFile:b1.rmvb mode:forTransfer RunTime:1406
End Copy File!