File copy is stuck in an infinite loop

Question

The below code seems to be stuck in an infinate loop. I have to terminate the program to stop it running.

Here's the output & the code -

File copied from c:\projects\test\buildlist.txt to c:\projects\test\newtest\buildlist.txt
File copied from c:\projects\test\GHTELE5S605A.jad to c:\projects\test\newtest\GHTELE5S605A.jad
File copied from c:\projects\test\GHTELE5S605A.jar to c:\projects\test\newtest\GHTELE5S605A.jar
File copied from c:\projects\test\GHTele5T240w400h.jad to c:\projects\test\newtest\GHTele5T240w400h.jad
File copied from c:\projects\test\GHTele5T240w400h.jar to c:\projects\test\newtest\GHTele5T240w400h.jar
File copied from c:\projects\test\newtest\buildlist.txt to c:\projects\test\newtest\newtest\buildlist.txt
File copied from c:\projects\test\newtest\GHTELE5S605A.jad to c:\projects\test\newtest\newtest\GHTELE5S605A.jad
File copied from c:\projects\test\newtest\GHTELE5S605A.jar to c:\projects\test\newtest\newtest\GHTELE5S605A.jar
File copied from c:\projects\test\newtest\GHTele5T240w400h.jad to c:\projects\test\newtest\newtest\GHTele5T240w400h.jad
File copied from c:\projects\test\newtest\GHTele5T240w400h.jar to c:\projects\test\newtest\newtest\GHTele5T240w400h.jar
File copied from c:\projects\test\newtest\newtest\buildlist.txt to c:\projects\test\newtest\newtest\newtest\buildlist.txt
File copied from c:\projects\test\newtest\newtest\GHTELE5S605A.jad to c:\projects\test\newtest\newtest\newtest\GHTELE5S605A.jad
File copied from c:\projects\test\newtest\newtest\GHTELE5S605A.jar to c:\projects\test\newtest\newtest\newtest\GHTELE5S605A.jar
File copied from c:\projects\test\newtest\newtest\GHTele5T240w400h.jad to c:\projects\test\newtest\newtest\newtest\GHTele5T240w400h.jad
File copied from c:\projects\test\newtest\newtest\GHTele5T240w400h.jar to c:\projects\test\newtest\newtest\newtest\GHTele5T240w400h.jar
File copied from c:\projects\test\newtest\newtest\newtest\buildlist.txt to c:\projects\test\newtest\newtest\newtest\newtest\buildlist.txt
File copied from c:\projects\test\newtest\newtest\newtest\GHTELE5S605A.jad to c:\projects\test\newtest\newtest\newtest\newtest\GHTELE5S605A.jad
File copied from c:\projects\test\newtest\newtest\newtest\GHTELE5S605A.jar to c:\projects\test\newtest\newtest\newtest\newtest\GHTELE5S605A.jar
File copied from c:\projects\test\newtest\newtest\newtest\GHTele5T240w400h.jad to c:\projects\test\newtest\newtest\newtest\newtest\GHTele5T240w400h.jad
File copied from c:\projects\test\newtest\newtest\newtest\GHTele5T240w400h.jar to c:\projects\test\newtest\newtest\newtest\newtest\GHTele5T240w400h.jar
File copied from c:\projects\test\newtest\newtest\newtest\newtest\buildlist.txt to c:\projects\test\newtest\newtest\newtest\newtest\newtest\buildlist.txt
File copied from c:\projects\test\newtest\newtest\newtest\newtest\GHTELE5S605A.jad to c:\projects\test\newtest\newtest\newtest\newtest\newtest\GHTELE5S605A.jad
File copied from c:\projects\test\newtest\newtest\newtest\newtest\GHTELE5S605A.jar to c:\projects\test\newtest\newtest\newtest\newtest\newtest\GHTELE5S605A.jar
File copied from c:\projects\test\newtest\newtest\newtest\newtest\GHTele5T240w400h.jad to c:\projects\test\newtest\newtest\newtest\newtest\newtest\GHTele5T240w400h.jad
File copied from c:\projects\test\newtest\newtest\newtest\newtest\GHTele5T240w400h.jar to c:\projects\test\newtest\newtest\newtest\newtest\newtest\GHTele5T240w400h.jar
File copied from c:\projects\test\newtest\newtest\newtest\newtest\newtest\buildlist.txt to c:\projects\test\newtest\newtest\newtest\newtest\newtest\newtest\buildlist.txt
File copied from c:\projects\test\newtest\newtest\newtest\newtest\newtest\GHTELE5S605A.jad to c:\projects\test\newtest\newtest\newtest\newtest\newtest\newtest\GHTELE5S605A.jad
File copied from c:\projects\test\newtest\newtest\newtest\newtest\newtest\GHTELE5S605A.jar to c:\projects\test\newtest\newtest\newtest\newtest\newtest\newtest\GHTELE5S605A.jar
File copied from c:\projects\test\newtest\newtest\newtest\newtest\newtest\GHTele5T240w400h.jad to c:\projects\test\newtest\newtest\newtest\newtest\newtest\newtest\GHTele5T240w400h.jad
File copied from c:\projects\test\newtest\newtest\newtest\newtest\newtest\GHTele5T240w400h.jar to c:\projects\test\newtest\newtest\newtest\newtest\newtest\newtest\GHTele5T240w400h.jar
File copied from c:\projects\test\newtest\newtest\newtest\newtest\newtest\newtest\buildlist.txt to c:\projects\test\newtest\newtest\newtest\newtest\newtest\newtest\newtest\buildlist.txt
File copied from c:\projects\test\newtest\newtest\newtest\newtest\newtest\newtest\GHTELE5S605A.jad to c:\projects\test\newtest\newtest\newtest\newtest\newtest\newtest\newtest\GHTELE5S605A.jad
File copied from c:\projects\test\newtest\newtest\newtest\newtest\newtest\newtest\GHTELE5S605A.jar to c:\projects\test\newtest\newtest\newtest\newtest\newtest\newtest\newtest\GHTELE5S605A.jar
File copied from c:\projects\test\newtest\newtest\newtest\newtest\newtest\newtest\GHTele5T240w400h.jad to c:\projects\test\newtest\newtest\newtest\newtest\newtest\newtest\newtest\GHTele5T240w400h.jad
File copied from c:\projects\test\newtest\newtest\newtest\newtest\newtest\newtest\GHTele5T240w400h.jar to c:\projects\test\newtest\newtest\newtest\newtest\newtest\newtest\newtest\GHTele5T240w400h.jar
File copied from c:\projects\test\newtest\newtest\newtest\newtest\newtest\newtest\newtest\buildlist.txt to c:\projects\test\newtest\newtest\newtest\newtest\newtest\newtest\newtest\newtest\buildlist.txt

-

public static void main(String args[]) throws IOException{

    args = new String[2];
    args[0] = "c:\\projects\\test";
    args[1] = "c:\\projects\\test\\newtest";

        File srcFolder = new File(args[0]);
        File destFolder = new File(args[1]);

        //make sure source exists
        if(!srcFolder.exists()){

           System.out.println("Directory does not exist.");
           //just exit
           System.exit(0);

        }else{

           try{
            copyFolder(srcFolder,destFolder);
           }catch(IOException e){
            e.printStackTrace();
            //error, just exit
                System.exit(0);
           }
        }

        System.out.println("Done");
    }

    public static void copyFolder(File src, File dest)
        throws IOException{

        if(src.isDirectory()){

            //if directory not exists, create it
            if(!dest.exists()){
               dest.mkdir();
               System.out.println("Directory copied from " 
                              + src + "  to " + dest);
            }

            //list all the directory contents
            String files[] = src.list();

            for (String file : files) {
               //construct the src and dest file structure
               File srcFile = new File(src, file);
               File destFile = new File(dest, file);
               //recursive copy
               copyFolder(srcFile,destFile);
            }

        }else{
            //if file, then copy it
            //Use bytes stream to support all file types
            InputStream in = new FileInputStream(src);
                OutputStream out = new FileOutputStream(dest); 

                byte[] buffer = new byte[1024];

                int length;
                //copy the file content in bytes 
                while ((length = in.read(buffer)) > 0){
                   out.write(buffer, 0, length);
                }

                in.close();
                out.close();
                System.out.println("File copied from " + src + " to " + dest);
        }
    }
}

Thank you for an help.

Answer 1

If you are not required to write the copy function yourself, you should use a library to do that. Like the Apache commons IO.

Otherwise check if you are not copying the destination (as source) to the destination.

Answer 2

Filter out the destination directory when looping over the listed files.

if (src.equals(destFolder)) {
    continue;
}

I recommend you use File[] files = src.listFiles(); instead of src.list().

And note that it is better style to put the array brackets on the type instead of the variable, that is File[] files instead of File files[].

Also note: You have a bug when reading files. InputStream.read(byte[]) may return 0 even if end of file hasn't been reached, check for != -1 instead of > 0.

Answer 3

The problem comes from the fact that you are copying files to a sub-directory of the source directory.

When listing the files and directories to copy, you should exclude the target directory, or else you'll indeed get stuck in an infinite loop :

String files[] = src.list();
for (String file : files) {
    // Test if the file is equal to the destination directory;
    // - if so, just skip it ! (continue)
    // - if not so, you can process the file
}

Answer 4

try{
    copyFolder(srcFolder,destFolder);     //  <-- this is where your problem lies
}catch(IOException e){

Your program goes into infinite recursion because inside this method, you're calling it once again for newly created directories.

You should rewrite it so it only recursively traverses the source directory.