MD5加密的三种实现方式

MD5加密本质相同，只是有不同的代码实现形式，暂时找到三种表现形式，贴出来与大家共享
第一种实现方式：

public static String md5(String str) {
		MessageDigest digest;
		try {
			digest = MessageDigest.getInstance("MD5");
			digest.reset();
			digest.update(str.getBytes());
			byte[] a = digest.digest();
			int len = a.length;
			StringBuilder sb = new StringBuilder(len << 1);
			for (int i = 0; i < len; i++) {
				sb.append(Character.forDigit((a[i] & 0xf0) >> 4, 16));
				sb.append(Character.forDigit(a[i] & 0x0f, 16));
			}
			return sb.toString();
		} catch (NoSuchAlgorithmException e) {
			e.printStackTrace();
		}
		return null;
	}

第二种实现方式：

public static String md5(String string) {
		if (string == null)
			return null;
		try {
			MessageDigest md = MessageDigest.getInstance("MD5");
			md.update(string.getBytes());
			byte[] buffer = md.digest();
			StringBuilder sb = new StringBuilder();
		    for (int i = 0; i<buffer.length; i++) {  
		        String s = String.format("%02x", buffer[i]);  
		        sb.append(s);  
		    }
		    return sb.toString();
		} catch (NoSuchAlgorithmException e) {
			e.printStackTrace();
		}
		return null;
	}

第三种实现方式：

private static String md5(String key) {
        MessageDigest hash = null;
        try {
            hash = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException e) {
            return null;
        }

        hash.update(key.getBytes());
        byte[] digest = hash.digest();
        StringBuilder builder = new StringBuilder();
        for (int b : digest) {
            builder.append(Integer.toHexString((b >> 4) & 0xf));
            builder.append(Integer.toHexString((b >> 0) & 0xf));
        }
        return builder.toString();
    }