StandardHasher.java

package ch.unibe.scg.cc;

import static com.google.common.base.Preconditions.checkNotNull;

import java.io.IOException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

import javax.inject.Inject;

import com.google.common.base.Charsets;

/** Performs no normalization. Simply computes the cryptographic hash of a string */
public class StandardHasher implements Hasher {
	final private static long serialVersionUID = 1L;

	/** Package private so that ShingleHasher can learn num of bytes. */
	transient MessageDigest md = makeDigest();

	@Inject
	StandardHasher() {}

	private void readObject(java.io.ObjectInputStream stream) throws IOException, ClassNotFoundException {
		stream.defaultReadObject();
		md = makeDigest();
	}

	@Override
	public byte[] hash(String document) {
		checkNotNull(document);

		return md.digest(document.getBytes(Charsets.UTF_8));
	}

	private static MessageDigest makeDigest() {
		try {
			return MessageDigest.getInstance("SHA1");
		} catch (NoSuchAlgorithmException e) {
			throw new RuntimeException("Couldn't find SHA1 digest. ", e);
		}
	}
}