Java实现文件拷贝的4种方法.-优快云博客

本文链接：https://blog.youkuaiyun.com/pyzheng/article/details/84539645

本文介绍了四种不同的文件复制方法，包括传统方式、NIO管道传输、内存映射文件写入及通道对通道复制，并对比了它们的实现细节。

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[url]http://blog.youkuaiyun.com/ta8210/article/details/2073817[/url]
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);
  }
 }

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++;
        }
    }

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();
        }
    }

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);
        }
    }