How to Calculate an MD5 File Checksum in Java?

Obtaining an MD5 File Checksum Utilizing Java

Despite the extensive capabilities of Java, a query concerning the computation of MD5 checksums for files initially garnered no straightforward solutions. To address this gap, we present a detailed illustration outlining the process using the DigestInputStream class.

The DigestInputStream functions as an input stream decorator, allowing for the simultaneous calculation of a digest while accessing the input stream as usual. This obviates the need for a separate data pass.

The following code snippet exemplifies the use of DigestInputStream:

MessageDigest md = MessageDigest.getInstance("MD5");
try (InputStream is = Files.newInputStream(Paths.get("file.txt"));
     DigestInputStream dis = new DigestInputStream(is, md)) 
{
  /* Read decorated stream (dis) to EOF as normal... */
}
byte[] digest = md.digest();

In this code:

• md represents an instance of the MD5 message digest algorithm.
• is is an input stream for the target file.
• dis is the DigestInputStream object that wraps is, performing MD5 calculation while reading the file.
• md.digest() retrieves the computed MD5 digest as an array of bytes.

Using this approach, you can effortlessly obtain the MD5 checksum of a file in Java.

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