Tutorials Java How to Generate Unique File Name When Saving a File in Java

How to Generate Unique File Name When Saving a File in Java

The following code snippet shows how to get a unique file name when saving the file in java. It first checks if already a file exists with the specified name, then it appends a number to the end.

public static File getUniqueFilePath(String parent, String child, String fileName) {
    File dir = new File(parent, child);
    String uniqueName = getUniqueFileName(parent, child, fileName);
    return new File(dir, uniqueName);
}

public static String getUniqueFileName(String parent, String child, String fileName) {
     final File dir = new File(parent, child);
     if (!dir.exists()) {
         dir.mkdirs();
     }

     int num = 0;
     final String ext = getFileExtension(fileName);
     final String name = getFileName(fileName);
     File file = new File(dir, fileName);
     while (file.exists()) {
         num++;
         file = new File(dir, name + "-" + num + ext);
     }
     return file.getName();
}

public static String getFileExtension(final String path) {
     if (path != null && path.lastIndexOf('.') != -1) {
         return path.substring(path.lastIndexOf('.'));
     }
     return null;
}


public static String getFileName(String fileName) {
     return fileName.substring(0, fileName.lastIndexOf('.'));
}
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  1. So, all that getUniqueFileName is doing is appending an integer to the filename. However it is not very efficient if a large number of files are going to be created and are not deleted. On every call, it starts counting from 0 to look for the next number that creates a unique filename. So, after 1000 files have been created, the next call will again start the while loop counting from 0 incrementing by 1 to reach 1001 that will finally give a unique file name.

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