java实现MD5算法

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

public class Main {

public static String md5(String str){
if(str == null || str.length() == 0){
return null;
}else{
MessageDigest MD5 = null;
try{
MD5 = MessageDigest.getInstance("md5");  //获取md5加密方法实例
}catch(NoSuchAlgorithmException e){
e.printStackTrace();
return null;
}

/*将byte类型转换为string类型，方便操作*/
byte[] t = MD5.digest(str.getBytes());
StringBuilder res = new StringBuilder();
for(byte tt : t){
String hex = Integer.toHexString(tt & 0xff);
if(hex.length() == 1){
hex = "0" + hex;
}
res.append(hex);
}
return res.toString();
}
}
public static void main(String[] args) {
System.out.println(md5("123"));
}

}