FileNameUtils.java

public class FileNameUtils {

    private static final String[] ILLEGAL_CHARACTERS =
            { "/", "\n", "\r", "\t", "\0", "\f", "`", "?", "*", "\\", "<", ">", "|", "\"", ":" };

    private static final String DEFAULT_SEPARATOR = "_";

    public static String normalizeFileName(String fileName, String separator){
        for (String illegalCharacter : ILLEGAL_CHARACTERS) {
            fileName = fileName.replace(illegalCharacter, separator);
        }
        return fileName;
    }

    public static String normalizeFileName(String fileName){
        return normalizeFileName(fileName, DEFAULT_SEPARATOR);
    }

    public static void main (String args[]){
        System.out.println(normalizeFileName("t?test:testk<.jpg", "*"));
        System.out.println(normalizeFileName("t?test:testk<.jpg"));
    }

}