Java Foundation Multi-threaded copy file for improved file copy performance

Using random Access file randomaccessfile and file channel Filechanne in IO stream to copy files can greatly improve the reading and writing efficiency of files, and make use of multi-thread to copy files to better performance. Depending on the size and requirements of the file, the number of threads can be determined. The approximate principle is that, depending on the number of threads given, the files are segmented, each thread is responsible for the size of the data = file length / number of threads, and the part that cannot be removed is left to the thread that is allocated for the last file. The following is the implementation code and their own understanding of the comments, there are many deviations please forgive me. Here are the brothers and even Java training

Summary of some of the code: for reference.

Program Implementation Class Code:

　　Importjava.io.RandomAccessFile;

　　Importjava.nio.channels.FileChannel;

　　Importjava.nio.channels.FileLock;

　　// define a Copythread class to inherit the Thread class

　　public class Copythreadextends thread{

　　Private String srcpath;// original file address

　　Private String destpath;// destination file address

　　private int Start,end;//start Specifies the starting position , end specifies the ending position

　　// construction Copythread method

　　Public Copythread (Stringsrcpath, String destpath, int start, int end) {

　　"http://blog.51cto.com/viewpic.php?refimg=" + This.srcpath = srcpath;// The source file path to copy

　　This.destpath = destpath;// copied to the file path

　　This.start = start;// copy start position

　　this.end = end;// Copy End location

　　}

　　// rewrite the run () method

　　public void Run () {

　　try {

　　// Create a read-only random Access file

　　Randomaccessfile in = Newrandomaccessfile (Srcpath, "R");

　　// Create a readable and writable random Access file

　　Randomaccessfile out = Newrandomaccessfile (DestPath, "RW");

　　In.seek (start);// jumps the input to the specified position

　　Out.seek (start);// write from specified position

　　FileChannel Inchannel =in.getchannel ();// file input Channel

　　FileChannel Outchannel =out.getchannel ();// file output channel

　　// Lock the area that needs operation , false means lock

　　Filelock lock = Outchannel.lock (Start, (End-start), false);

　　// transfers bytes from this channel to the Outchannel channel of the given writable byte.

　　Inchannel.transferto (Start, (End-start), Outchannel);

　　lock.release ();// release lock

　　out.close ();// close file from inside to outside

　　in.close ();// Close File

　　} catch (Exception e) {

　　E.printstacktrace ();

　　}

　　}

　　}

Test Class Code:

　　Import Java.io.File;

　　public class Testmain {

　　public static Voidmain (string[] args) {

　　// The source file path to copy

　　String srcpath = "f:\\sun\\ class note \\aa.txt";

　　String destpath = "f:\\sun\\ class note \\aa copy . txt";

　　// Get source file length

　　File F = new file (Srcpath);

　　Long len = F.length ();

　　int count = 3;// The number of threads required

　　int onenum = (int) (len/count);// Thread-Responsible file length, cast to int type

　　// use for loop to divide the first part of the file with the second part ( cycles can be adjusted according to the number of threads defined )

　　for (int i = 0; I <count-1; i++) {

　　//onenum * I start position, Onenum * (i + 1) The length of the data to be copied

　　Copythread ct = newcopythread (Srcpath, DestPath, Onenum * i,onenum * (i + 1));

　　Ct.start ();

　　}

　　// the portion of the file length cannot be divisible into the last paragraph of processing

　　Copythread ct = newcopythread (Srcpath, DestPath, Onenum * (count-1), (int) len);

　　Ct.start ();

　　}

　　}

Java Foundation Multi-threaded copy file for improved file copy performance