How to generate a checksum for an java object

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I'm looking for a solution to generate a checksum for any type of Java object, which remains the same for every execution of an application that produces the same object.

I tried it with Object.hashCode(), but the api says

....This integer need not remain consistent from one execution of an application to another execution of the same application.

I had similar problem (generating good hashcode for XML files) and I found out that the best solution is to use MD5 through MessageDigest or in case you need something faster: Fast MD5. Please notice that even if Object.hashCode would be the same every time it is anyway too short (only 32 bits) to ensure high uniqueness. I think 64 bits is a minimum to compute good hash code. Please be aware that MD5 generates 128 bits long hash code, which should is even more that needed in this situation.

Of course to use MessageDigest you need serialize (in your case marshall) the object first.

Checksum of a Java Object · GitHub, public void bubbleSort(int randValue, int sizeArray) throws NoSuchAlgorithmException, IOException{. CheckObject l = new CheckObject();. BigInteger sum  To create checksum for a file, you will need to read the content of file byte by byte in chunks; and then generate hash for it using below manner. This function takes two arguments: The message digest algorithm’s implementation. A file for which checksum needs to be generated.

public static String getChecksum(Serializable object) throws IOException, NoSuchAlgorithmException {
    ByteArrayOutputStream baos = null;
    ObjectOutputStream oos = null;
    try {
        baos = new ByteArrayOutputStream();
        oos = new ObjectOutputStream(baos);
        oos.writeObject(object);
        MessageDigest md = MessageDigest.getInstance("MD5");
        byte[] thedigest = md.digest(baos.toByteArray());
        return DatatypeConverter.printHexBinary(thedigest);
    } finally {
        oos.close();
        baos.close();
    }
}

MD5 Hashing in Java, Below is another simpler approach for generating MD5 checksums using com.​google.common.io.Files.hash : ? 1. 2. 3. How to unzip files in java? How to generate checksum value for for a file in java? How to compress and store objects using zip utility? How to decompress the compressed objects using zip utility? How to zip a file using ZipFile class? How to compress a file in GZip format? How to uncompress a file from GZip format?

Example

private BigInteger checksum(Object obj) throws IOException, NoSuchAlgorithmException {

    if (obj == null) {
      return BigInteger.ZERO;   
    }

    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    ObjectOutputStream oos = new ObjectOutputStream(baos);
    oos.writeObject(obj);
    oos.close();

    MessageDigest m = MessageDigest.getInstance("SHA1");
    m.update(baos.toByteArray());

    return new BigInteger(1, m.digest());
}

What is an MD5 checksum value and what is it used for?, How do you find the checksum of a string in Java? Java – Create file checksum with SHA and MD5 MD5 algorithm to generate a checksum for a file. hex from a sha 224 and 512 hash.i would love to do it in java

I think you should look at serialization. Serialization mechanism needs to solve similar problem, so you can look how it's implemented.

But if you describe the problem you're trying to solve you'll probably get more precise solution.

Hash Code and Checksum - what's the difference?, Learn how to create checksums in Java. Object – this helps with code re-use and negates the need to create new instances of Checksum. While it's essential to understand the roles that hashCode() and equals() methods play, we don't have to implement them from scratch every time, as most IDEs can generate custom hashCode() and equals() implementations and since Java 7, we got an Objects.hash() utility method for comfortable hashing: Objects.hash(name, email)

If you control the source, you can implement hashCode() so it will be consistent from one execution to another.

Checksums in Java, A checksum hash is an encrypted sequence of characters obtained after applying certain algorithms. In this post, we will learn to generate the checksum hash for  CertUtil is a Windows built-in command line installed as part of certificate services, but it also offers a switch -hashfile that allows you to generate the hash string using a specified algorithm. For example, running the following command generates an SHA-512 checksum for an executable file called lsr.exe. certutil -hashfile z:\desktop\lsr.exe SHA512

Generate SHA or MD5 file checksum hash in java, 1.1 Generate a file checksum with a SHA256 algorithm. FileCheckSumSHA.java. package com.mkyong.hashing; import java.io.FileInputStream  MD5 is a widely used cryptographic hash function, which produces a hash of 128 bit. In this article we shall see how will see different approaches to create MD5 hashes using various Java libraries . 2.

Java - Create file checksum with SHA and MD5, Let's create a Checksum object and use it to filter an input or output stream. When writing a byte to the CheckedOutputStream , the checksum is  A hash is a unique value corresponding to a given data with the following properties, It is impossible to arrive at the original message from hash. Two different messages practically cannot have the same hash. Modifying message changes the corresponding hash. It is easy to generate the hash value with the above properties.

Checksumming, I'm looking for a solution to generate a checksum for any type of Java object, which remains the same for every execution of an application that produces the  On runtime, JVM processes hash code for each object and give it on interest. When we alter an objects’ state, JVM calculates its hash code again which may result in memory leak. To make things work what we have to do is make sure that state change for a key object does not change the hash code of object i.e. the key must have properly

Comments
  • Can you add a link to the quotation?
  • @Roman: java.sun.com/j2se/1.5.0/docs/api/java/lang/…
  • int checksum(Object o) { return 1;} fills your requirements :-)
  • In more detail, I have to check if objects (marshalled xml request) between two application calls are the same or not.
  • @Alex: then why don't you compare the original XML for equality? That would probably be a much easier task than what you are attempting (even if you make it tolerate changes in whitespace or similar slight differences).
  • thank you all for your answers. I calculate a MD5 from the marshalled request.