java 文件复制 四种方法
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
Java代码
publicstaticlong 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=newbyte[length];
while(true){
int ins=in.read(buffer);
if(ins==-1){
in.close();
out.flush();
out.close();
returnnew Date().getTime()-time;
}else
out.write(buffer,0,ins);
}
}
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
Java代码
publicstaticlong 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();
returnnew 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++;
}
}
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)
Java代码
publicstaticlong 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=newbyte[length];
while(true){
if(inC.position()==inC.size()){
inC.close();
outC.force();
out.close();
returnnew Date().getTime()-time;
}
if((inC.size()-inC.position())<length){
length=(int)(inC.size()-inC.position());
}else{
length=20971520;
}
b=newbyte[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();
}
}
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
Java代码
publicstaticlong 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();
returnnew 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);
}
}
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!
解释: 在测试结果中看到 古老方式,和管道向管道传输是最快的,,,,,为什么呢?
我分析是这样的,由于另外2种方法内部都使用了 字节数组作为缓存中转,在加上NIO内部有一个贴近系统的缓存区,这无意就增加了另一个缓存器,所以相对于这2个方法就要慢许多,,如果不使用 字节数组作为数据中转的话相信速度会更快的..
不过比较惊讶的是 管道向管道传输的速度还是真挺吓人,,,
我的机器是 IDE硬盘120G 硬盘缓存2MB, 内存1GB, CPU AMD2800+
