Copying files from one directory to another in Java

Question

Hello,

I want to copy files from one directory to another (subdirectory) using Java. I have a directory, dir, with text files. I iterate over the first 20 files in dir, and want to copy them to another directory in the dir directory, which I have created right before the iteration. In the code, I want to copy the review (which represents the ith text file or review) to trainingDir. How can I do this? There seems not to be such a function (or I couldn't find). Thank you.

boolean success = false;
File[] reviews = dir.listFiles();
String trainingDir = dir.getAbsolutePath() + "/trainingData";
File trDir = new File(trainingDir);
success = trDir.mkdir();
for(int i = 1; i <= 20; i++) {
    File review = reviews[i];

}

Answer 1

you use renameTo() – not obvious, I know ... but it's the Java equivalent of move ...

Answer 2

There is no file copy method in the Standard API (yet). Your options are:

• Write it yourself, using a FileInputStream, a FileOutputStream and a buffer to copy bytes from one to the other - or better yet, use FileChannel.transferTo()
• User Apache Commons' FileUtils
• Wait for NIO2 in Java 7

Answer 3

The NIO classes make this pretty simple.

http://www.javalobby.org/java/forums/t17036.html

Answer 4

If you want to copy a file and not move it you can code like this.

private static void copyFile(File sourceFile, File destFile)
  throws IOException {
 if (!sourceFile.exists()) {
  return;
 }
 if (!destFile.exists()) {
  destFile.createNewFile();
 }
 FileChannel source = null;
 FileChannel destination = null;
 source = new FileInputStream(sourceFile).getChannel();
 destination = new FileOutputStream(destFile).getChannel();
 if (destination != null && source != null) {
  destination.transferFrom(source, 0, source.size());
 }
 if (source != null) {
  source.close();
 }
 if (destination != null) {
  destination.close();
 }

}

Answer 5

The example below from Java Tips is rather straight forward. I have since switched to Groovy for operations dealing with the file system - much easier and elegant. But here is the Java Tips one I used in the past. It lacks the robust exception handling that is required to make it fool-proof.

 public void copyDirectory(File sourceLocation , File targetLocation)
    throws IOException {

        if (sourceLocation.isDirectory()) {
            if (!targetLocation.exists()) {
                targetLocation.mkdir();
            }

            String[] children = sourceLocation.list();
            for (int i=0; i<children.length; i++) {
                copyDirectory(new File(sourceLocation, children[i]),
                        new File(targetLocation, children[i]));
            }
        } else {

            InputStream in = new FileInputStream(sourceLocation);
            OutputStream out = new FileOutputStream(targetLocation);

            // Copy the bits from instream to outstream
            byte[] buf = new byte[1024];
            int len;
            while ((len = in.read(buf)) > 0) {
                out.write(buf, 0, len);
            }
            in.close();
            out.close();
        }
    }

Answer 6

For now this should solve your problem

File source = new File("H:\\work-temp\\file");
File desc = new File("H:\\work-temp\\file2");
try {
    FileUtils.copyDirectory(source, desc);
} catch (IOException e) {
    e.printStackTrace();
}

Using third party tools instead of writing all utilities by ourself seems to be a better idea. It can save time and other valuable resources.

Answer 7

You seem to be looking for the simple solution (a good thing), to which I would recommend using Apache Common's FileUtil.copyDirectory

Copies a whole directory to a new location preserving the file dates.

This method copies the specified directory and all its child directories and files to the specified destination. The destination is the new location and name of the directory.

The destination directory is created if it does not exist. If the destination directory did exist, then this method merges the source with the destination, with the source taking precedence.

Your code could like nice and simple like this:

File trgDir = new File("/tmp/myTarget/");
File srcDir = new File("/tmp/mySource/");

FileUtils.copyDirectory(srcDir, trgDir);

Answer 8

Use org.apache.commons.io.FileUtils. It's so handy