DigestOutputStream not reporting the correct digest value

Question

I have the following inside a unit test to try and figure out why my DigestOutputStream is not calculating the correct digest for a test .jpg I have in the classpath.

The assertArrayEquals() passes but the final assertEquals() fails with different results.

// the .jpg is 32394 bytes

final MessageDigest md5 = MessageDigest.getInstance("md5");
md5.update(ByteStreams.toByteArray(getInputStream()));
final String h0 = DatatypeConverter.printHexBinary(md5.digest());
System.out.println("MD5 = " + h0); // MD5 = 98BE96C5B9C8D0E41723BBA6E508AADC

// raw MessageDigest from InputStream to ByteArrayOutputStream
final MessageDigest md5a = MessageDigest.getInstance("md5");
final ByteArrayOutputStream baosa = new ByteArrayOutputStream(32394);
ByteStreams.copy(getInputStream(), baosa);
md5a.update(baosa.toByteArray());
final String ha = DatatypeConverter.printHexBinary(md5a.digest());
assertArrayEquals(ByteStreams.toByteArray(getInputStream()),baosa.toByteArray());
assertEquals(h0,ha);

// raw DigestOutputStream to ByteArrayOutputStream
final ByteArrayOutputStream baosb = new ByteArrayOutputStream(32394);
final DigestOutputStream dos = new DigestOutputStream(baosb, MessageDigest.getInstance("md5"));
ByteStreams.copy(getInputStream(), dos);
final String hb = DatatypeConverter.printHexBinary(dos.getMessageDigest().digest());
assertArrayEquals(baosa.toByteArray(), baosb.toByteArray());
assertEquals(h0,hb);  // <-- this is where it fails

Failure:

MD5 = 98BE96C5B9C8D0E41723BBA6E508AADC

org.junit.ComparisonFailure: 
Expected :98BE96C5B9C8D0E41723BBA6E508AADC
Actual   :D41D8CD98F00B204E9800998ECF8427E

Why isn't the DigestOutputStream returning the correct value?

And for completeness here is what I am reading in for each of the cases:

private InputStream getInputStream()
{
    return Thread.currentThread().getContextClassLoader().getResourceAsStream("Al_Bundy_Shoot_Me_$12.jpg");
}

Here is the image I am reading in off the classpath in all cases:

Answer 1

Solution

I needed to close the DigestOutputStream before trying to get the .digest() off of it.

final DigestOutputStream dos = new DigestOutputStream(baosb, MessageDigest.getInstance("md5"));
ByteStreams.copy(getInputStream(), dos);
dos.close(); // <-- this fixed the problem!
final String hb = DatatypeConverter.printHexBinary(dos.getMessageDigest().digest());

Apparently .flush() makes it behave correctly as well.