一文搞懂Java MD5算法的原理及实现

 /**  
     * 用MD5算法进行加密  
     * @param str 需要加密的字符串  
     * @return MD5加密后的结果  
	 * @throws UnsupportedEncodingException 
     */    
public static String encodeMD5String(String str) {    
       	return getMD5(str);
    }

 /**
     * MD5编码方法， 该方法存在漏洞，特殊情况下编码后的字符串只有31位长度
     * @param str
     * @param method
     * @return
     * @throws UnsupportedEncodingException
     */
private static String encode(String str, String method) throws UnsupportedEncodingException {    
        MessageDigest md = null;    
        String dstr = null;    
        try {    
            md = MessageDigest.getInstance(method);    
            md.update(str.getBytes("UTF-8"));    
            dstr = new BigInteger(1, md.digest()).toString(16);    
        } catch (NoSuchAlgorithmException e) {    
            e.printStackTrace();    
        }    
        return dstr;    
    }

/**
     * MD5编码方法
     * @param message
     * @return
     */
    public static String getMD5(String message) {  
        MessageDigest messageDigest = null;  
        StringBuffer md5StrBuff = new StringBuffer();  
        try {  
            messageDigest = MessageDigest.getInstance("MD5");  
            messageDigest.reset();  
            messageDigest.update(message.getBytes("UTF-8"));  
              
            byte[] byteArray = messageDigest.digest();  
            for (int i = 0; i < byteArray.length; i++)   
            {  
                if (Integer.toHexString(0xFF & byteArray[i]).length() == 1)  
                    md5StrBuff.append("0").append(Integer.toHexString(0xFF & byteArray[i]));  
                else  
                    md5StrBuff.append(Integer.toHexString(0xFF & byteArray[i]));  
            }  
        } catch (Exception e) {  
            throw new RuntimeException();  
        }  
        return md5StrBuff.toString().toUpperCase();//字母大写  
    } 

 /**
     * 加密
     * @param content
     * @return
     */
    public static String encrypt(String content) {
    	String password = "12345678dd";
    	byte[] encryptResult = encrypt(content, password);  
        String encryptResultStr = parseByte2HexStr(encryptResult);  
        return encryptResultStr;
    }

/**
     * 加密
     * @param content
     * @param password
     * @return
     */
    public static String encryptStr(String content, String password) {
    	byte[] encryptResult = encrypt(content, password);  
        return parseByte2HexStr(encryptResult);
    }

/**
     * 解密
     * @param encryptResultStr
     * @return
     * @throws UnsupportedEncodingException
     */
    public static String decrypt(String encryptResultStr) throws UnsupportedEncodingException {
    	String password = "12345678dd";
    	 byte[] decryptFrom = parseHexStr2Byte(encryptResultStr);  
	     byte[] decryptResult = decrypt(decryptFrom, password);  
	     // 解密内容进行解码  
	     String result = new String(decryptResult, UTF8);  
	     return result;
    }

/**
     * 解密
     * @param encryptStr
     * @param password
     * @return
     * @throws UnsupportedEncodingException
     */
    public static String decryptStr(String encryptStr, String password) throws UnsupportedEncodingException {
		byte[] decryptFrom = parseHexStr2Byte(encryptStr);
		byte[] decryptResult = decrypt(decryptFrom, password);
		// 解密内容进行解码
		return new String(decryptResult, UTF8);
    }