Java: How to create SHA-1 for a file?

Question

What is the best way to create a SHA-1 for a very large file in pure Java6? How to implement this method:

public abstract String createSha1(java.io.File file); 

Answer 1

Use the MessageDigest class and supply data piece by piece. The example below ignores details like turning byte[] into string and closing the file, but should give you the general idea.

public byte[] createSha1(File file) throws Exception  {     MessageDigest digest = MessageDigest.getInstance("SHA-1");     InputStream fis = new FileInputStream(file);     int n = 0;     byte[] buffer = new byte[8192];     while (n != -1) {         n = fis.read(buffer);         if (n > 0) {             digest.update(buffer, 0, n);         }     }     return digest.digest(); }