DigestUtils.java

/*
 * Copyright 2002-2012 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.xiongyingqi.util;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 * Miscellaneous methods for calculating digests.
 * <p>Mainly for internal use within the framework; consider
 * <a href="http://commons.apache.org/codec/">Apache Commons Codec</a> for a
 * more comprehensive suite of digest utilities.
 *
 * @author Arjen Poutsma
 * @see org.apache.commons.codec.digest.DigestUtils
 * @since 3.0
 */
public abstract class DigestUtils {

    private static final String MD5_ALGORITHM_NAME = "MD5";

    private static final char[] HEX_CHARS =
            {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};

    /**
     * Calculate the MD5 digest of the given bytes.
     *
     * @param bytes the bytes to calculate the digest over
     * @return the digest
     */
    public static byte[] md5Digest(byte[] bytes) {
        return digest(MD5_ALGORITHM_NAME, bytes);
    }

    /**
     * Return a hexadecimal string representation of the MD5 digest of the given
     * bytes.
     *
     * @param bytes the bytes to calculate the digest over
     * @return a hexadecimal digest string
     */
    public static String md5DigestAsHex(byte[] bytes) {
        return digestAsHexString(MD5_ALGORITHM_NAME, bytes);
    }

    /**
     * Append a hexadecimal string representation of the MD5 digest of the given
     * bytes to the given {@link StringBuilder}.
     *
     * @param bytes   the bytes to calculate the digest over
     * @param builder the string builder to append the digest to
     * @return the given string builder
     */
    public static StringBuilder appendMd5DigestAsHex(byte[] bytes, StringBuilder builder) {
        return appendDigestAsHex(MD5_ALGORITHM_NAME, bytes, builder);
    }

    /**
     * Creates a new {@link java.security.MessageDigest} with the given algorithm. Necessary
     * because {@code MessageDigest} is not thread-safe.
     */
    private static MessageDigest getDigest(String algorithm) {
        try {
            return MessageDigest.getInstance(algorithm);
        } catch (NoSuchAlgorithmException ex) {
            throw new IllegalStateException("Could not find MessageDigest with algorithm \"" + algorithm + "\"", ex);
        }
    }

    private static byte[] digest(String algorithm, byte[] bytes) {
        return getDigest(algorithm).digest(bytes);
    }

    private static String digestAsHexString(String algorithm, byte[] bytes) {
        char[] hexDigest = digestAsHexChars(algorithm, bytes);
        return new String(hexDigest);
    }

    private static StringBuilder appendDigestAsHex(String algorithm, byte[] bytes, StringBuilder builder) {
        char[] hexDigest = digestAsHexChars(algorithm, bytes);
        return builder.append(hexDigest);
    }

    private static char[] digestAsHexChars(String algorithm, byte[] bytes) {
        byte[] digest = digest(algorithm, bytes);
        return encodeHex(digest);
    }

    private static char[] encodeHex(byte[] bytes) {
        char chars[] = new char[32];
        for (int i = 0; i < chars.length; i = i + 2) {
            byte b = bytes[i / 2];
            chars[i] = HEX_CHARS[(b >>> 0x4) & 0xf];
            chars[i + 1] = HEX_CHARS[b & 0xf];
        }
        return chars;
    }

}