MessageDigest类提供MD5或SHA等加密算法

MessageDigest可使用的加密方法有MD2MD5SHA-1SHA-256SHA-384SHA-512，使用时候只替换相应参数值即可

MessageDigest md5 = MessageDigest.getInstance("MD5");

MessageDigest md5 = MessageDigest.getInstance("MD2");

MessageDigest md5 = MessageDigest.getInstance("SHA-1");

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以MD5加密为例的代码，代码中使用两种方式转换为十六进制格式数据输出

@Test
    public void test() throws NoSuchAlgorithmException, UnsupportedEncodingException {
        String str = "a";
        MessageDigest md5 = MessageDigest.getInstance("MD5");
        byte[] bytes = md5.digest(str.getBytes("utf-8"));
        StringBuilder stringBuilder = new StringBuilder();
        for (int i = 0; i < bytes.length; i++) {
            //0x表示十六进制，使用&0xff是在byte转int时，做补码处理，保证二进制数据一致性，计算机存储的是补码
            //整数转十六进制使用Integer的toHexString方法
            String tempStr = Integer.toHexString(bytes[i] & 0xff);
            if (tempStr.length() == 1)
                //如果长度为1补0
                stringBuilder.append("0").append(tempStr);
            else
                stringBuilder.append(tempStr);
            //分割符如：0c:c1:75:b9:c0:f1:b6:a8:31:c3:99:e2:69:77:26:61
            if (i < bytes.length - 1)
                stringBuilder.append(":");
        }
        System.out.println(stringBuilder.toString());
        stringBuilder=new StringBuilder();
        for (int i = 0; i < bytes.length; i++) {
            int chartIndex = bytes[i] & 0xff;
            //整数转十六进制，小于16的为0~F，要补0输出
            if (chartIndex < 16) {
                stringBuilder.append("0");
            }
            stringBuilder.append(Integer.toHexString(chartIndex));
            if (i < bytes.length - 1)
                stringBuilder.append(":");
        }
        System.out.println(stringBuilder.toString());
    }