MD5全称是Message-Digest Algorithm 5(信息-摘要算法)

//确定计算方法
MessageDigest md5 = MessageDigest.getInstance("MD5");

//jdk1.8新增Base64
String newstr = Base64.getEncoder().encodeToString(md5.digest(str.getBytes("utf-8")));

//1.8之前使用sum.misc.Base64Encoder(此类没有访问权限，在tr.jar中添加访问权限：sun/misc/*)
BASE64ENcoder base64 = new BASE64ENcoder();
base64.encode(md5.digest(str.getBytes("utf-8")));

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;

import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;

public class MD5Demo {
    
    public static void main(String[] args) {
        
        String password = "admin12345";
        
        try {
            
            //确定md5加密算法
            MessageDigest md = MessageDigest.getInstance("md5");
            //通过md5计算摘要；返回的是字节数组，是不可清晰读取的，所以需要再次转换成可读字符串
            byte [] bytes = md.digest(password.getBytes("UTF-8"));
            System.out.println(Arrays.toString(bytes));
            
            /**
            如下对加密后的MD5值直接输出字符串是乱码“t堛1付NW斱?る�璢”，所以要用一个编码算法重新转成一个可读的字符串
            String mdstr = new String(bytes);
            System.out.println(mdstr);
            */
            
                        
            // a-z A-Z 0-9 / * BASE64编码算法，转成可读的字符串
            /**
             * jdk1.8版本，将将MD5值转成可读字符串
            String str = Base64.getEncoder().encodeToString(bytes);
            */
            
            //jdk1.8以前版本；将MD5值转成可读字符串
            BASE64Encoder base64 = new BASE64Encoder();
            String str = base64.encode(bytes);
            System.out.println(str);
            
            //还原成md5值
            BASE64Decoder decoder = new BASE64Decoder();
            byte[] bs = decoder.decodeBuffer(str);
            System.out.println(Arrays.toString(bs));
            
            
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } 
        
    }

}

举例引用

import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;
import sun.misc.BASE64Encoder;

public class testmd5 {
    private static String savepasswd = "dIjjMbi2TleU2j+k6xCtXQ==";
    public static void main(String[] args) {
        System.out.println(login("admin12345"));

    }
    
    //判断所输入的密码经过md5加密后是否与原密文一致
    private static boolean login(String password){
        if(savepasswd.equals(md5(password))){
            return true;
        }else{
            return false;
        }
    }
    
    //计算md5的工具方法
    private static String md5(String password){
        try {
            //确定md5加密算法
            MessageDigest md = MessageDigest.getInstance("md5");
            //通过md5计算摘要
            byte [] bytes = md.digest(password.getBytes("UTF-8"));
            
            //md5值转成可读字符串
            BASE64Encoder base64 = new BASE64Encoder();
            String str = base64.encode(bytes);
            return str;
            
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        return null;
    }

}