MessageDigest类提供MD5或SHA等加密算法

@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());
}