Copy data from one csv file to another csv file using java

You can simply use the Java 7 NIO2:

Eg:
If you want to copy a file from one location to another, simply call:

Files.copy(fromPath, toPath);

If you want to move:

Files.move(fromPath, toPath);

With Java 7 features, you don't need to write hard code for files handling.
Hope it help.

Java 7 NIO2 Tutorial Link

Edited:
But your requirement is not file copy but you want to write uploaded file contents to existing file, you can also simply use the Java 7 NIO2 features.

Eg:

private static void writeFileAsAppend() throws IOException {
        List<String> lines = readFileAsSequencesOfLines();
        Path path = getWriteFilePath();         
        Files.write(path, lines, StandardOpenOption.APPEND);
}

private static List<String> readFileAsSequencesOfLines() throws IOException {
        Path path = getReadFilePath();          
        List<String> lines = Files.readAllLines(path);    
        return lines;
}

private static Path getReadFilePath() {
        Path path = Paths
                .get(".\\ReadMe.csv");    
        return path.normalize();
}

private static Path getWriteFilePath() {
        Path path = Paths
                .get(".\\WriteMe.csv");    
        return path;
}