1.JWT是什么？

JWT，英文全称JSON Web Token：JSON网络令牌。为了在网络应用环境间传递声明而制定的一种基于JSON的开放标准(RFC 7519)。这个规范允许我们使用JWT在客户端和服务端之间传递安全可靠的信息。 JWT是一个轻便的安全跨平台传输格式，定义了一个紧凑自包含的方式，用于通信双方之间作为 JSON 对象安全地传递信息。此信息可以通过数字签名进行验证和信任。

• 紧凑：这个字符串简洁，数据量小，传输速度快，能通过URL参数、HTTP请求提交的数据以及HTTP Header的方式进行传递。
• 自包含：负载中包含很多信息，比如用户的ID等。别人拿到这个字符串，就能拿到这些关键的业务信息，从而避免再通过数据库查询等方式得到它们。

JWT的结构 JWT由三段信息用.连接构成的字符串。

Header.Payload.Signature 例如：

• Header头部

承载两部分信息：token类型和采用的加密算法

{    "typ": "JWT",   "alg": "HS256" }

token类型：JWT 加密算法：HS256

• Payload负载

存放有效信息的地方

iss: jwt签发者 sub: jwt所面向的用户 aud: 接收jwt的一方 exp: 过期时间戳(jwt的过期时间，这个过期时间必须要大于签发时间) nbf: 定义在什么时间之前，该jwt都是不可用的 iat: jwt的签发时间 jti: jwt的唯一身份标识，主要用来作为一次性token，从而回避重放攻击

• Signature签名

对头部及负载内容进行签证。采用Header中声明的算法，接收三个参数：base64编码的Header、base64编码的Payload和密钥（secret）进行运算。密钥secret是保存在服务端的，服务端会根据这个密钥进行生成token和进行验证。

2.环境搭建

参考代码仓库里面的mysql模块，这里只贴出docker-compose.yml

version: '3' services:   mysql:     image: registry.cn-hangzhou.aliyuncs.com/zhengqing/mysql:5.7     container_name: mysql_3306     restart: unless-stopped                                        volumes:       - "./mysql/my.cnf:/etc/mysql/my.cnf"       - "./mysql/init-file.sql:/etc/mysql/init-file.sql"       - "./mysql/data:/var/lib/mysql" #      - "./mysql/conf.d:/etc/mysql/conf.d"       - "./mysql/log/mysql/error.log:/var/log/mysql/error.log"       - "./mysql/docker-entrypoint-initdb.d:/docker-entrypoint-initdb.d" # init sql script directory -- tips: it can be excute  when `/var/lib/mysql` is empty     environment:                        # set environment,equals docker run -e       TZ: Asia/Shanghai       LANG: en_US.UTF-8       MYSQL_ROOT_PASSWORD: root         # set root password       MYSQL_DATABASE: demo              # init database name     ports:                              # port mappping       - "3306:3306"

运行

docker-compose -f docker-compose.yml -p mysql5.7 up -d

初始化表

DROP TABLE IF EXISTS `jwt_user`;  CREATE TABLE `jwt_user`(  `id` varchar(32) CHARACTER SET utf8 NOT NULL COMMENT '用户ID',  `username` varchar(100) CHARACTER SET utf8 NULL DEFAULT NULL COMMENT '登录账号',  `password` varchar(255) CHARACTER SET utf8 NULL DEFAULT NULL COMMENT '密码' )ENGINE = InnoDB CHARACTER SET = utf8 COMMENT = '用户表' ROW_FORMAT = Compact;  INSERT INTO jwt_user VALUES('1','admin','123');

3.代码工程

实验目标：实现JWT的签发和验证

pom.xml

<?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">     <parent>         <artifactId>springboot-demo</artifactId>         <groupId>com.et</groupId>         <version>1.0-SNAPSHOT</version>     </parent>     <modelVersion>4.0.0</modelVersion>      <artifactId>jwt</artifactId>      <properties>         <maven.compiler.source>8</maven.compiler.source>         <maven.compiler.target>8</maven.compiler.target>     </properties>     <dependencies>         <dependency>             <groupId>org.springframework.boot</groupId>             <artifactId>spring-boot-starter-web</artifactId>         </dependency>          <dependency>             <groupId>org.springframework.boot</groupId>             <artifactId>spring-boot-autoconfigure</artifactId>         </dependency>         <!--mysql-->         <dependency>             <groupId>mysql</groupId>             <artifactId>mysql-connector-java</artifactId>             <version>8.0.29</version>         </dependency>         <dependency>             <groupId>org.springframework.boot</groupId>             <artifactId>spring-boot-starter-jdbc</artifactId>         </dependency>         <dependency>             <groupId>com.baomidou</groupId>             <artifactId>mybatis-plus-boot-starter</artifactId>             <version>3.5.1</version>         </dependency>         <dependency>             <groupId>org.projectlombok</groupId>             <artifactId>lombok</artifactId>         </dependency>         <dependency>             <groupId>org.springframework.boot</groupId>             <artifactId>spring-boot-starter-test</artifactId>             <scope>test</scope>         </dependency>         <dependency>             <groupId>com.alibaba</groupId>             <artifactId>fastjson</artifactId>             <version>1.2.47</version>         </dependency>         <dependency>             <groupId>io.jsonwebtoken</groupId>             <artifactId>jjwt</artifactId>             <version>0.9.1</version>         </dependency>         <dependency>             <groupId>com.auth0</groupId>             <artifactId>java-jwt</artifactId>             <version>3.4.0</version>         </dependency>       </dependencies> </project>

application.yaml

spring:   datasource:     driver-class-name: com.mysql.cj.jdbc.Driver     url: jdbc:mysql://localhost:3306/demo?useSSL=false&useUnicode=true&characterEncoding=UTF-8&serverTimezone=GMT     username: root     password: root  server:   port: 8088

Jwt生成

package com.et.jwt.service;  import com.auth0.jwt.JWT; import com.auth0.jwt.algorithms.Algorithm;  import com.et.jwt.entity.User; import org.springframework.stereotype.Service;  import java.time.Instant; import java.time.LocalDateTime; import java.time.ZoneId; import java.util.Date;   @Service("TokenService")  public class TokenService {     long  outHours=1;     public String getToken(User user) {         Instant instant = LocalDateTime.now().plusHours(outHours).atZone(ZoneId.systemDefault()).toInstant();         Date expire = Date.from(instant);         String token="";         // save information  to token ,such as: user id and Expires time         token= JWT.create()                 .withAudience(user.getId())                 .withExpiresAt(expire)                 .sign(Algorithm.HMAC256(user.getPassword()));         // use HMAC256 to generate token,key is user's password         return token;     } }

jwt验证

package com.et.jwt.interceptor;  import com.auth0.jwt.JWT; import com.auth0.jwt.JWTVerifier; import com.auth0.jwt.algorithms.Algorithm; import com.auth0.jwt.exceptions.JWTDecodeException; import com.auth0.jwt.exceptions.JWTVerificationException;  import com.et.jwt.annotation.PassToken; import com.et.jwt.annotation.UserLoginToken; import com.et.jwt.entity.User; import com.et.jwt.service.UserService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.method.HandlerMethod; import org.springframework.web.servlet.HandlerInterceptor; import org.springframework.web.servlet.ModelAndView;  import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.lang.reflect.Method; import java.util.Date;   public class AuthenticationInterceptor implements HandlerInterceptor {     @Autowired     UserService userService;     @Override     public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object object) throws Exception {         //  get token  from http header         String token = httpServletRequest.getHeader("token");         if(!(object instanceof HandlerMethod)){             return true;         }         HandlerMethod handlerMethod=(HandlerMethod)object;         Method method=handlerMethod.getMethod();         //check is included @passtoken annotation? jump if have         if (method.isAnnotationPresent(PassToken.class)) {             PassToken passToken = method.getAnnotation(PassToken.class);             if (passToken.required()) {                 return true;             }         }         //check is included @UserLoginToken ?         if (method.isAnnotationPresent(UserLoginToken.class)) {             UserLoginToken userLoginToken = method.getAnnotation(UserLoginToken.class);             if (userLoginToken.required()) {                 // excute verify                 if (token == null) {                     throw new RuntimeException("token invalid，please login again");                 }                 // get  user id  from  token                 String userId;                 try {                     userId = JWT.decode(token).getAudience().get(0);                 } catch (JWTDecodeException j) {                     throw new RuntimeException("401");                 }                 User user = userService.findUserById(userId);                 if (user == null) {                     throw new RuntimeException("user is not exist，please login again");                 }                 // verify token                 JWTVerifier jwtVerifier = JWT.require(Algorithm.HMAC256(user.getPassword())).build();                 try {                     jwtVerifier.verify(token);                     if (JWT.decode(token).getExpiresAt().before(new Date())) {                         throw new RuntimeException("token Expires");                     }                  } catch (JWTVerificationException e) {                     throw new RuntimeException("401");                 }                  return true;             }         }         return true;     }      @Override     public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {      }     @Override     public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {      } }

以上只是一些关键代码，所有代码请参见下面代码仓库

代码仓库

• https://github.com/Harries/springboot-demo

4.测试

• 启动Spring Boot应用
• 登录系统http://localhost:8088/api/login?username=admin&password=123

{  "user": {  "username": "admin",  "password": "123",  "id": "1"  },  "token": "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJhdWQiOiIxIn0.ihOZFzg3ZGIbBMneRy-4RMqors1P3nuO-wRJnQtTzWQ" }

• 在header里面设置 token，访问http://localhost:8088/api/getMessage

5.引用

• https://www.v2ex.com/t/817906
• http://www.liuhaihua.cn/archives/710374.html
• https://github.com/ChuaWi/SpringBoot-JWT/tree/master

6.Questions

这里留2个问题给读者

1. 过期了如何刷新token呢？保证过期时候重新登录，而不是后台自动刷新，一直不过期？
2. 如果要实现强制下线用户功能，该如何实现呢？