应用 java 进行文件拷贝 信赖很多人都邑用,,不过效力上是否最好呢?
比来看了看NIO决意试一试 java NIO 到底有什么机能的提拔.
第一种办法:古老的体式格式
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);
}
}
办法的2参数分别是原始文件,和拷贝的目标文件.这里不做过多介绍.
实现办法很简单,分别对2个文件构建输入输出流,并且应用一个字节数组作为我们内存的缓存器, 然后应用流从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种办法:应用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++;
}
}
实现办法:在第一种实现办法根蒂根基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
办法3:内存文件景象形象写(读文件没有应用文件景象形象,有爱好的可以归去尝尝,,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();
}
}
实现办法:跟伤2个例子不一样,这里写文件流没有应用管道而是应用内存文件映射(假设文件f2在内存中).在轮回中从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种办法: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);
}
}
这里实现体式格式与第3种实现体式格式很类似,不过没有应用内存暗射.
下面是对49.3MB的文件进行拷贝的测试时候(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!
注:以上文章摘自网络。如有侵权,请联系!一定会在24小时之内删除。。。