InputStream is=new FileInputStream(new File("xx.txt"));
OutputStream os=new FileOutputStream(nwe File(xx_copy.txt));

int len;	//len是arr数组的有效元素个数
byte[] arr=new byte[1024];
while((len=is.read(arr))!=-1){
	os.write(arr,0,len);
}

is.close();
os.close();



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//普通方法
InputStream is=new FileInputStream(new File("xx.txt"));
OutputStream os=new FileOutputStream(nwe File(xx_copy.txt));

int b;		//接收读取到的字节byte的int
while((b=is.read())!=-1){
	os.write(len);
}

is.close();
os.close();