Detect changed files in a directory (java 8) from digest or checksum

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I'm looking for a simple way to detect if files have changed in a directory between reboots to avoid unnecessary synchronization. What would be the simplest way to do this in java 8 libraries? Should I XOR the md5 digest of each file or XOR the checksums of each file?

ATM we don't need to handle going into sub directories.

Also we should not be using an OS event to detect this change as the method to detect will only be called at startup. The number of files in the directory can change between different versions of the application but these files will not generally change between reboots.

This looks like a relevant post:

Generate SHA or MD5 file checksum hash in java, In this post, we will learn to generate the checksum hash for files. You can also create checksum of file to detect any possible change in file by third party e.g. license files. private static String getFileChecksum(MessageDigest digest, File file) throws IOException How to Copy Directories in Java� You can also create checksum of file to detect any possible change in file by third party e.g. license files. You provide licenses to clients which they may upload to your server. You can cross verify the checksum of file to verify that license file has not been modified after creation. Read More : MD5, SHA, PBKDF2, BCrypt examples. 2.

Is the file's modified time useful in your situation? Md5sum is a preciser way for some situations.

Would md5 hashes allow detection of synced files?, Yes, MD5 is almost guaranteed to detect any change in files you produce. to Windows) that synchronizes files and directories from one location to another while I used the following Java code to find the difference (and demo the usage of both i < noOfLoopIterations; i++) { md5Digest = md5.digest( randomByteBuffer); }� Calculate File Checksum. Here is a class that will generate a checksum hash in one of the registered hash algorithms like MD5 or SHA. This class allows you to simply create a checksum of a file using one of the popular hashing algorithms.

Here's a routine I'm looking to generate a hash from all files in a directory.

 * Recursively compute a single md5 signature of all files in a directory. Is typically 
 * used to determine if a file in a directory or any of the sub directories have been 
 * modified since the last digest was taken.
public class DirectoryDigest {

    MessageDigest md = null;

    public DirectoryDigest() {
        try {
            md = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException e) {

    public void update(Path dirPath) {
        update(dirPath, null);

    public synchronized void update(Path dirPath, String extension) {

        try {
            Files.newDirectoryStream(dirPath).forEach(file -> {
                if (!Files.isDirectory(file) && file.getFileName().toString().endsWith(extension)) {
                    if (extension != null && !file.getFileName().toString().endsWith(extension)) {
                        System.out.println("not processing: " + file.getFileName());
                    try {
                        byte[] bytes = Files.readAllBytes(file);
                    } catch (IOException e) {
                } else {
                    update(file, extension);
        } catch (IOException e) {

     * Returns md5 digest signature and resets the digest object.
     * @return
    public String digest() {
        return String.format("%032X", new BigInteger(1, md.digest()));

It is used like this:

DirectoryDigest dd = new DirectoryDigest();
dd.update(csConfigDirPath, ".xml");
String currentPeripheralHash = dd.digest();

Java 8 release changes, In order to determine if a release is the latest, the following Security Baseline page Other notes: New Oracle Specific JDK 8 Updates System Property to Fallback to and the legacy JCE jurisdiction files don't exist in the legacy lib/ security directory, Signed by "CN=weak_signer" Digest algorithm: MD5 (weak) Signature� The MD5 checksum for a file is a 128-bit value, something like a fingerprint of the file. It can be useful both for comparing the files and their integrity control. It can be useful both for comparing the files and their integrity control.

How to Generate MD5 checksum for Files in Java, You can generate MD 5 checksums for files in Java using MessageDigest or any open source library like Apache commons For those who are not familiar with checksum, it's a fixed-size datum generated from a block of data to detect any accidental change in Anonymous July 17, 2014 at 8:04 AM. If two files have the same MD5 checksum value, then there is a high probability that the two files are the same. After downloading an MQ software installation package, you can compute the MD5 checksum on the installation file. The MD5 checksum or MD5 hash is a more secure alternative to the checksums obtained from the "sum" or "cksum" commands.

Java - Create file checksum with SHA and MD5, In this article, we will show you how to use a SHA-256 and MD5 algorithm to generate a checksum for a file. MessageDigest. i have been asked to produce a software which demands a person to enter either a text,file etc and produces in return hex from a sha 224 and 512 hash.i would love to do it in java but not only don’t i know how to call a file in a java program and i don’t how to go about writing the sha 224 and 512 programs.please help me

How to get MD5 checksum for any given file in Java? Use commons , Use commons-codec's DigestUtils. if some unauthorized person changes the value of that file without your The MD5 checksum for a file is a 128-bit value , something like a Java program which creates and returns MD5 values for a given file. Tutorial on File and Directory Operations Check it out. The above function can be called multiple times when say you are reading a long file. Then finally we need to use digest function to generate a hash code: public byte[] digest()

  • Would this help?
  • @LyjuIEdwinson Thanks but I'm specifically not looking to detect file changes by OS events as this routine will only be triggered at system startup.
  • What exactly is meant by "to avoid unnecessary synchronization"? Are you mirroring files to another directory? Then maybe you shuold better just use rsync instead of rolling your own.
  • @Axel It's specific to our application, when these files are modified we need to resync our controller to our database and this process takes a while. Basically there is a large file that is being refactored into smaller xml files via xinclude statements and now I want to dynamically detect if these smaller files have been modified instead of maintaining a list of files in the code. We previously just cached a copy of the md5 of our large file.
  • @simgineer You should carefully read the file notification, as it not only fired at system startup.
  • Appreciate the insight. BTW - This isn't a file sync scenario. we parse configs files (which are large) and then if there is a change there is a DB update (which takes time). It is a legacy program. Not something where it makes sense to use rsync.
  • You can handle that with rsync. It just takes a bit of imagination. Alternatively, if this is not a (remote) file system sync problem you could simply compare files in an "old" and "new" file tree. There are Linux / UNIX utilities to do that too.
  • Yes, and if you go with @StephenC's suggestion, and you are using at least Java 12 (I know, it's not quite common for production code), you should check out Files.mismatch(Path, Path) which was introduced in Java 12.
  • Hi @StephenC and Axel, I believe what is being suggested w rsync requires the original directory structure to be available and we don't have access to the old file system, all we store from the old file system is a catch or checksum of the files that matter. The synchronization routine runs after the old configuration files have been overwritten with the new configuration files. To clarify the synchronization is not between two file systems but a set of configuration files and a settings matrix engine backed by mysql tables. The xml define setting types and the DB stores data per profile.
  • I think we prefer checksums or digest to timestamps in case the systems time is not correctly set.