Java实现MD5注册登录以及生成token和解决跨域问题

Java实现MD5注册登录以及生成token和解决跨域问题

在这个demo中，整合了ssm框架，注册的时候会将密码进行加密，登录的时候会根据username和userid生成token，并编写了拦截器，对方法进行了拦截，除了登录和注册，其他接口必须掺入token才可以，通过前端调用接口时出现了跨域问题，在此也进行了解决

首先是SSM整合的配置文件

pom文件

<?xml version="1.0" encoding="UTF-8"?>

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.st</groupId>
  <artifactId>study</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>war</packaging>

  <name>studyMaven Webapp</name>
  <!-- FIXME change it to the project's website -->
  <url>http://www.example.com</url>

  <properties>
    <project.build.source.Encoding>UTF-8</project.build.source.Encoding>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
    <spring.version>5.0.2.RELEASE</spring.version>
  </properties>

  <dependencies>
      <!--MyBatis相关-->
      <dependency>
          <groupId>org.mybatis</groupId>
          <artifactId>mybatis</artifactId>
          <version>3.4.5</version>
      </dependency>
      <!--MyBatis整合Spring的包-->
      <dependency>
          <groupId>org.mybatis</groupId>
          <artifactId>mybatis-spring</artifactId>
          <version>1.3.0</version>
      </dependency>
      <dependency>
          <groupId>tk.mybatis</groupId>
          <artifactId>mapper</artifactId>
          <version>4.0.4</version>
      </dependency>
      <!--数据库相关-->
      <dependency>
          <groupId>mysql</groupId>
          <artifactId>mysql-connector-java</artifactId>
          <version>8.0.18</version>
          <scope>runtime</scope>
      </dependency>
      <dependency>
          <groupId>com.alibaba</groupId>
          <artifactId>druid</artifactId>
          <version>1.1.10</version>
      </dependency>
      <!--Spring相关-->
      <dependency>
          <groupId>org.springframework</groupId>
          <artifactId>spring-context</artifactId>
          <version>5.0.2.RELEASE</version>
      </dependency>
      <dependency>
          <groupId>org.springframework</groupId>
          <artifactId>spring-tx</artifactId>
          <version>5.0.2.RELEASE</version>
      </dependency>
      <dependency>
          <groupId>org.springframework</groupId>
          <artifactId>spring-jdbc</artifactId>
          <version>5.0.2.RELEASE</version>
      </dependency>
      <dependency>
          <groupId>org.springframework</groupId>
          <artifactId>spring-test</artifactId>
          <version>5.0.2.RELEASE</version>
      </dependency>
      <dependency>
          <groupId>org.aspectj</groupId>
          <artifactId>aspectjweaver</artifactId>
          <version>1.8.7</version>
      </dependency>
      <!--SpringMVC相关-->
      <dependency>
          <groupId>org.springframework</groupId>
          <artifactId>spring-web</artifactId>
          <version>${spring.version}</version>
      </dependency>
      <dependency>
          <groupId>org.springframework</groupId>
          <artifactId>spring-webmvc</artifactId>
          <version>${spring.version}</version>
      </dependency>
      <dependency>
          <groupId>com.fasterxml.jackson.core</groupId>
          <artifactId>jackson-databind</artifactId>
          <version>2.9.0</version>
      </dependency>
      <dependency>
          <groupId>com.fasterxml.jackson.core</groupId>
          <artifactId>jackson-core</artifactId>
          <version>2.9.0</version>
      </dependency>
      <dependency>
          <groupId>com.fasterxml.jackson.core</groupId>
          <artifactId>jackson-annotations</artifactId>
          <version>2.9.0</version>
      </dependency>
      <dependency>
          <groupId>commons-fileupload</groupId>
          <artifactId>commons-fileupload</artifactId>
          <version>1.3.1</version>
      </dependency>
      <dependency>
          <groupId>commons-io</groupId>
          <artifactId>commons-io</artifactId>
          <version>2.4</version>
      </dependency>
      <!--web相关-->
      <dependency>
          <groupId>javax.servlet</groupId>
          <artifactId>javax.servlet-api</artifactId>
          <version>3.1.0</version>
          <scope>provided</scope>
      </dependency>
      <dependency>
          <groupId>javax.servlet.jsp</groupId>
          <artifactId>jsp-api</artifactId>
          <version>2.2</version>
          <scope>provided</scope>
      </dependency>
      <dependency>
          <groupId>javax.servlet</groupId>
          <artifactId>jstl</artifactId>
          <version>1.2</version>
          <scope>runtime</scope>
      </dependency>
      <!--日志-->
      <dependency>
          <groupId>log4j</groupId>
          <artifactId>log4j</artifactId>
          <version>1.2.12</version>
      </dependency>
      <dependency>
          <groupId>org.slf4j</groupId>
          <artifactId>slf4j-api</artifactId>
          <version>1.6.6</version>
      </dependency>
      <dependency>
          <groupId>org.slf4j</groupId>
          <artifactId>slf4j-log4j12</artifactId>
          <version>1.6.6</version>
      </dependency>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.12</version>
      <scope>test</scope>
    </dependency>
      <!--生成token-->
      <dependency>
          <groupId>com.auth0</groupId>
          <artifactId>java-jwt</artifactId>
        <version>3.3.0</version>
      </dependency>
  </dependencies>


  <build>
    <plugins>
      <!-- Compile -->
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.3</version>
        <configuration>
          <source>1.8</source>
          <target>1.8</target>
          <encoding>UTF-8</encoding>
        </configuration>
      </plugin>
      <!-- 打包跳过Test -->
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-surefire-plugin</artifactId>
        <version>2.18.1</version>
        <configuration>
          <skipTests>true</skipTests>
        </configuration>
      </plugin>
      <!--   配置Tomcat插件 -->
      <plugin>
        <groupId>org.apache.tomcat.maven</groupId>
        <artifactId>tomcat7-maven-plugin</artifactId>
        <version>2.2</version>
        <configuration>
          <!--<path>/${project.artifactId}</path>-->
          <path>/</path>
          <port>80</port>
        </configuration>
      </plugin>
      <!-- 资源文件拷贝插件 -->
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-resources-plugin</artifactId>
        <version>2.7</version>
        <configuration>
          <encoding>UTF-8</encoding>
        </configuration>
      </plugin>
    </plugins>
    <resources>
      <!-- 使用Maven部署的时候，xml和properties配置文件也一起部署到Tomcat -->
      <resource>
        <directory>src/main/java</directory>
        <includes>
          <include>**/*.properties
          **/*.xml</include>
        </includes>
        <filtering>false</filtering>
      </resource>
      <!-- 默认是以下配置 -->
      <resource>
        <directory>src/main/resources</directory>
        <includes>
          <include>**/*.properties
          **/*.xml</include>
        </includes>
        <filtering>false</filtering>
      </resource>
    </resources>
  </build>
</project>

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
                      http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         version="3.0">
  <!-- 跨域请求 -->
  <filter>
    <filter-name>SimpleCORSFilter</filter-name>
    <filter-class>com.study.utils.SimpleCORSFilter</filter-class>
    <init-param>
      <param-name>IsCross</param-name>
      <param-value>true</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>SimpleCORSFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
    <!--1.支持restful的过滤器(如果需要就配置在所有过滤器之前)-->
    <!-- 解决put和delete请求无法获取表单数据的问题 -->
    <filter>
        <filter-name>HttpMethodFilter</filter-name>
        <filter-class>org.springframework.web.filter.HttpPutFormContentFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>HttpMethodFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
    <!-- 将POST请求转化为DELETE或者是PUT 要用_method指定真正的请求参数 -->
    <filter>
        <filter-name>HiddenHttpMethodFilter</filter-name>
        <filter-class>org.springframework.web.filter.HiddenHttpMethodFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>HiddenHttpMethodFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

    <!--2.SpringMVC的DispatcherServlet-->
    <servlet>
        <servlet-name>dispatcherServlet</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <!-- 配置Servlet的初始化参数，读取springmvc的配置文件，创建spring容器 -->
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:springmvc.xml</param-value>
        </init-param>
        <!-- 配置servlet启动时加载对象 -->
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>dispatcherServlet</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

    <!--3.乱码过滤器-->
    <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
        <!-- 设置编码为UTF-8 -->
        <init-param>
            <param-name>encoding</param-name>
            <param-value>UTF-8</param-value>
        </init-param>
        <init-param>
            <param-name>forceEncoding</param-name>
            <param-value>true</param-value>
        </init-param>
    </filter>
    <!-- 过滤所有请求 -->
    <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
    <!--4.Spring容器(要在服务器启动的时候就创建Spring容器)-->
    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>
    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:springMybatis.xml</param-value>
    </context-param>
</web-app>

jdbc.properties
顺便说一下，我数据库用的是mysql.8.0，如果版本不一样，需要修改依赖的版本

jdbc.driverClassName=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/study?characterEncoding=utf8&serverTimezone=Asia/Shanghai
jdbc.username=root
jdbc.password=root

log4j

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss}  %m%n

log4j.appender.file=org.apache.log4j.FileAppender
log4j.appender.file.File=D:/Mylog.log
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss}  %l  %m%n

log4j.rootLogger=debug, stdout

springMybatis.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:aop="http://www.springframework.org/schema/aop"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context.xsd">

    <!--组件扫描-->
    <context:component-scan base-package="com.study.Service"></context:component-scan>

    <!--加载properties配置文件-->
    <context:property-placeholder location="classpath:jdbc.properties"/>

    <!--数据源-->
    <bean name="dataSource" class="com.alibaba.druid.pool.DruidDataSource">
        <property name="driverClassName" value="${jdbc.driverClassName}"></property>
        <property name="url" value="${jdbc.url}"></property>
        <property name="username" value="${jdbc.username}"></property>
        <property name="password" value="${jdbc.password}"></property>
    </bean>

    <!-- Session工厂 -->
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="configLocation" value="classpath:sqlMapConfig.xml" />
        <!--加载mapper.xml 文件-->
        <property name="mapperLocations" value="classpath*:mapper/*Mapper.xml"></property>
        <!-- 配置别名 -->
        <property name="typeAliasesPackage" value="com.study.Entity"></property>
    </bean>

    <!--接口扫描 -->
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="com.study.Mapper" />
    </bean>

</beans>

sqlMapconfig.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <settings>
        <!-- 开启驼峰自动映射 -->
        <setting name="mapUnderscoreToCamelCase" value="true" />
    </settings>
</configuration>**

springMVC.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="
       http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/mvc
       http://www.springframework.org/schema/mvc/spring-mvc.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context.xsd">

    <!-- 配置spring创建容器时要扫描的包 -->
    <context:component-scan base-package="com.study.Controller"></context:component-scan>
    
    <!--自定义消息转换器的编码,解决后台传输json回前台时，中文乱码问题-->
    <mvc:annotation-driven >
        <mvc:message-converters register-defaults="true">
            <bean class="org.springframework.http.converter.StringHttpMessageConverter" >
                <property name = "supportedMediaTypes">
                    <list>
                        <value>application/json;charset=utf-8</value>
                        <value>text/html;charset=utf-8</value>
                        <!-- application 可以在任意 form 表单里面 enctype 属性默认找到 -->
                        <value>application/x-www-form-urlencoded</value>
                    </list>
                </property>
            </bean>
            <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter" ></bean>
        </mvc:message-converters>
    </mvc:annotation-driven>

    <!-- 配置拦截器 -->
    <mvc:interceptors>
        <mvc:interceptor>
            <!-- 哪些方法进行拦截 -->
            <mvc:mapping path="/**"/>
            <!-- 哪些方法不进行拦截-->
            <mvc:exclude-mapping path="/user/login"/>
            <mvc:exclude-mapping path="/user/register"/>
            <!-- 注册拦截器对象 -->
            <bean class="com.study.utils.TokenIeInterceptor"/>
        </mvc:interceptor>
    </mvc:interceptors>

    <!-- 接口跨域配置 -->
    <mvc:cors>
        <mvc:mapping path="/**"
                     allowed-origins="*"
                     allowed-methods="POST, GET, OPTIONS, DELETE, PUT"
                     allowed-headers="Content-Type, Access-Control-Allow-Headers, Authorization, X-Requested-With"
                     allow-credentials="true" />
    </mvc:cors>
</beans>

接下来是代码

实体类
在此我就不粘贴get/set方法了
result类，返回的结果集

public class Result {
    private String msg;  //返回的信息
    private boolean status;  //是否成功
    private Map Data;    //返回的数据
   }

user类

public class User {
    private Integer id;
    private String username;
    private String password;
    private String realname;
    }

controller层的

@RestController
@RequestMapping("user")
public class loginController {
    @Autowired
    private loginService loginService;

    /**
     * 注册账号
     * @param user
     * @return
     */
    @RequestMapping("register")
    public Result register(User user){
        //将密码通过MD5进行加密,再存进去
        user.setPassword(MD5Utils.MD5Encrypt(user.getPassword()));
        //注册账号
        int register = loginService.register(user);
        if(register>0){
            return new Result("注册成功",true, null);
        }
        return new Result("注册失败",false, null);
    }

    /**
     * 登录并生成token
     * @param user
     * @return
     */
    @RequestMapping("login")
    public Result login(User user){
        //将用户的密码进行加密
        user.setPassword(MD5Utils.MD5Encrypt(user.getPassword()));
        //调用登录方法
        User loginUser = loginService.login(user);
        //如果登录的用户存在的话，生成token
        if(loginUser!=null){
            //生成token
            String token = JwtUtils.sign(loginUser.getUsername(), loginUser.getId());
            if (token!=null){
                return new Result("登录成功",true, null);
            }else {
                return new Result("token为空",false, null);
            }
        }
        return new Result("该用户不存在",false, null);
    }
}

service层代码

public interface loginService {
    User login(User user);

    int register(User user);
}

实现类的代码
在实现登录的时候，因为密码进行了加密，所以我在这里是先将登录的密码进行加密，然后到数据库去查询看是否有对应用户。
但这样并不安全，因为一般的MD5加密的话同样的密码加密结果是一样，如果多个用户密码一样的话，一旦破译会使多个用户受到牵连。
如何解决？
可以使用BCrypt+SpringSecurity进行解决，
大体思路是：
（1）在注册账号时候通过BCrypt（BCrypt可以理解成md5+随机salt）对密码进行加密,将加密的密码存入数据库
（2）登录的时候输入用户名和密码,根据用户名去数据库中查询用户信息，
（3）SpringSecurity框架会将输入的明文密码使用同样的算法(md5+同样的salt)进行加密和数据库中查询出来的密文密码进行比对

感兴趣的话大家可以先搜索一下，我之后会在总结如何使用的

@Service
public class loginServiceImpl implements loginService {
    @Autowired
    private loginMapper loginMapper;

    @Override
    public int register(User user) {
        int register = loginMapper.register(user);
        return register;
    }

    @Override
    public User login(User user) {
        //将用户的密码进行加密
        User loginUser = loginMapper.login(user);
        return loginUser;
    }
}

Mapper层

@Repository
public interface loginMapper {

    User login(User user);

    int register(User user);
}

Mapper文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.study.Mapper.loginMapper">
<!--    注册用户-->
    <insert id="register" parameterType="User">
        insert into User(username,password) values(#{username},#{password})
    </insert>

    <!--    根据用户名查找用户-->
    <select id="selectUser" parameterType="User" resultType="User">
        select * from User where username=#{username}
    </select>

<!--    根据用户名和密码查找用户-->
    <select id="login" parameterType="User" resultType="User">
        select * from User where username=#{username} and password = #{password}
    </select>

</mapper>

工具类：
JwtUtils .java：用于生成token和验证token的，这里面使用的是jwt生成的，借鉴于网上的资料，token会比较长，token的生成方式还有很多种，仅供参考
token生成详细解释： https://blog.csdn.net/KKKun_Joe/article/details/81878231

public class JwtUtils {
     //过期时间20分钟
    private static  final long EXPIRE_TIME=20*60*1000;
    private static final String TOKEN_SELECT="ZCEQIUBFKSJBFJH2020BQWE";

    /**
     * 加密
     * @return
     */
    /*生成token令牌*/
    public static String sign(String username,int userId) {
        try {
        //过期时间
        Date date=new Date(System.currentTimeMillis());
        //设置加密算法和密匙
        Algorithm algorithm = null;
            algorithm = Algorithm.HMAC256(TOKEN_SELECT);
        //设置头部信息
        Map<String,Object> header=new HashMap<>(2);
        header.put("typ","JWT");
        header.put("alg","HS256");
        //附带username，userID 的信息，生成签名
        String sign = JWT.create().withHeader(header)
                .withClaim("loginName", username)
                .withClaim("user_id", userId)
                .withExpiresAt(date)
                .sign(algorithm);
            return sign;
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
            return null;
        }

    }

    /**
     * 验证token
     */
    public static boolean verify(String token){
        try {
            Algorithm algorithm = Algorithm.HMAC256(TOKEN_SELECT);
            JWTVerifier verify = JWT.require(algorithm).build();
            DecodedJWT verify1 = verify.verify(token);
            return true;
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
            return false;
        }
    }
}

TokenIeInterceptor .java
这是一个拦截器，在调用接口的时候必须通过拦截器，进行过滤，jdk1.8中HandlerInterceptor 都是默认方法，所以必须在配置文件中进行配置才可以重写生效，请查看springmvc.xml

public class TokenIeInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        response.setCharacterEncoding("UTF-8");
        String token =request.getHeader("token");
        if (token!=null){
            //验证token
            boolean result = JwtUtils.verify(token);
            if (result){
                return true;
            }
        }
        return false;
    }
}

SimpleCORSFilter .java
因为token的生成是参考网上的，也许是我的问题，所以前端调用接口的时候显示跨域，这个类用于解决跨域问题，也需要在配置文件里配置，如果不存在跨域可无视

public class SimpleCORSFilter implements Filter {
    private boolean isCross = false;

    @Override
    public void destroy() {
        isCross = false;
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        if (isCross) {
            HttpServletRequest httpServletRequest = (HttpServletRequest) request;
            HttpServletResponse httpServletResponse = (HttpServletResponse) response;
            System.out.println("拦截请求: " + httpServletRequest.getServletPath());
            httpServletResponse.setHeader("Access-Control-Allow-Origin", "*");
            httpServletResponse.setHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS, DELETE");
            httpServletResponse.setHeader("Access-Control-Max-Age", "0");
            httpServletResponse.setHeader("Access-Control-Allow-Headers",
                    "Origin, No-Cache, X-Requested-With, If-Modified-Since, Pragma, Last-Modified, Cache-Control, Expires, Content-Type, X-E4M-With,userId,token");
            httpServletResponse.setHeader("Access-Control-Allow-Credentials", "true");
            httpServletResponse.setHeader("XDomainRequestAllowed", "1");
        }
        chain.doFilter(request, response);
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        String isCrossStr = filterConfig.getInitParameter("IsCross");
        isCross = isCrossStr.equals("true") ? true : false;
        System.out.println(isCrossStr);
    }
}

MD5Utils.java

public class MD5Utils {
      public static String MD5Encrypt(String str){
        try {
            MessageDigest md = MessageDigest.getInstance("MD5");
            md.update(str.getBytes());
            byte[]byteDigest = md.digest();
            int i;
            StringBuffer buf = new StringBuffer("");
            for (int offset = 0; offset < byteDigest.length; offset++) {
                i = byteDigest[offset];
                if (i < 0)
                    i += 256;
                if (i < 16)
                    buf.append("0");
                buf.append(Integer.toHexString(i));
            }
            return buf.toString();
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
            return null;
        }
    }
}

有些东西也是参考网上的资料，会有不足，仅供参考