spring集成jwt验证方式，token验证

为什么要告别session？有这样一个场景，系统的数据量达到千万级，需要几台服务器部署，当一个用户在其中一台服务器登录后，用session保存其登录信息，其他服务器怎么知道该用户登录了？（单点登录），当然解决办法有，可以用spring-session。如果该系统同时为移动端服务呢？移动端通过url向后台要数据，如果用session，通过sessionId识别用户，万一sessionId被截获了，别人可以利用sessionId向后台要数据，就有安全隐患了。所以有必要跟session说拜拜了。服务端不需要存储任何用户的信息，用户的验证应该放在客户端，jwt就是这种方式！

什么是jwt？

最详细的是官网：https://jwt.io/

这里以java的ssm框架为例，集成jwt。

1.pom.xml 导入jwt的包

 <!-- jwt -->
   <!-- https://mvnrepository.com/artifact/com.auth0/java-jwt -->
   <dependency>
    <groupId>com.auth0</groupId>
    <artifactId>java-jwt</artifactId>
    <version>2.2.0</version>
   </dependency>

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2.编写jwt的工具类，有加密解密功能就好

import com.auth0.jwt.JWTSigner;
import com.auth0.jwt.JWTVerifier;
import com.auth0.jwt.internal.com.fasterxml.jackson.databind.ObjectMapper;

import java.util.HashMap;
import java.util.Map;

public class JWT {
    private static final String SECRET = "XX#$%()(#*!()!KL<><MQLMNQNQJQK sdfkjsdrow32234545fdf>?N<:{LWPW";

    private static final String EXP = "exp";

    private static final String PAYLOAD = "payload";

    //加密，传入一个对象和有效期
    public static <T> String sign(T object, long maxAge) {
        try {
            final JWTSigner signer = new JWTSigner(SECRET);
            final Map<String, Object> claims = new HashMap<String, Object>();
            ObjectMapper mapper = new ObjectMapper();
            String jsonString = mapper.writeValueAsString(object);
            claims.put(PAYLOAD, jsonString);
            claims.put(EXP, System.currentTimeMillis() + maxAge);
            return signer.sign(claims);
        } catch(Exception e) {
            return null;
        }
    }

    //解密，传入一个加密后的token字符串和解密后的类型
    public static<T> T unsign(String jwt, Class<T> classT) {
        final JWTVerifier verifier = new JWTVerifier(SECRET);
        try {
            final Map<String,Object> claims= verifier.verify(jwt);
            if (claims.containsKey(EXP) && claims.containsKey(PAYLOAD)) {
                long exp = (Long)claims.get(EXP);
                long currentTimeMillis = System.currentTimeMillis();
                if (exp > currentTimeMillis) {
                    String json = (String)claims.get(PAYLOAD);
                    ObjectMapper objectMapper = new ObjectMapper();
                    return objectMapper.readValue(json, classT);
                }
            }
            return null;
        } catch (Exception e) {
            return null;
        }
    }

}

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3.jwt有了，ssm要如何去利用，用户验证的第一步是登录，登录时根据用户传来的username和password到数据库验证身份，如果合法，便给该用户jwt加密生成token

//处理登录
    @RequestMapping(value="login", produces = "application/json; charset=utf-8")
    public @ResponseBody ResponseData login(HttpServletRequest request, @RequestParam( "email") String email,
            @RequestParam("password") String password) {
        Login login = new Login();
        login.setEmail(email);
        login.setPassword(password);
        ResponseData responseData = ResponseData.ok();
        //先到数据库验证
        Integer loginId = userService.checkLogin(login);
        if(null != loginId) {
            User user = userService.getUserByLoginId(loginId);
            login.setId(loginId);
            //给用户jwt加密生成token
            String token = JWT.sign(login, 60L* 1000L* 30L);
            //封装成对象返回给客户端
            responseData.putDataValue("loginId", login.getId());
            responseData.putDataValue("token", token);
            responseData.putDataValue("user", user);
        }
        else{
            responseData =  ResponseData.customerError();
        }
        return responseData;
    }

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4.在用户登录时，把loginId和token返回给前台，以后用户每次请求时，都得带上这两个参数，后台拿到token后解密出loginId，与用户传递过来的loginId比较，如果相同，则说明用户身份合法。因为是每个登录过后的每个请求，这里用springmvc的拦截器做

<mvc:interceptors>
    <mvc:interceptor>
        <!-- 匹配的是url路径， 如果不配置或/**,将拦截所有的Controller -->
        <mvc:mapping path="/**" />
        <!-- /register 和 /login 不需要拦截-->
        <mvc:exclude-mapping path="/register" />
        <mvc:exclude-mapping path="/login" />
        <bean class="com.xforce.charles.interceptor.TokenInterceptor"></bean>
    </mvc:interceptor>
    <!-- 当设置多个拦截器时，先按顺序调用preHandle方法，然后逆序调用每个拦截器的postHandle和afterCompletion方法 -->
    </mvc:interceptors> 

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5.拦截器代码

import java.io.PrintWriter;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

import com.alibaba.fastjson.JSONObject;
import com.xforce.charles.model.Admin;
import com.xforce.charles.model.Login;
import com.xforce.charles.util.JWT;
import com.xforce.charles.util.ResponseData;

public class TokenInterceptor implements HandlerInterceptor{

    public void afterCompletion(HttpServletRequest request,
            HttpServletResponse response, Object handler, Exception arg3)
            throws Exception {
    }

    public void postHandle(HttpServletRequest request, HttpServletResponse response,
            Object handler, ModelAndView model) throws Exception {
    }

    //拦截每个请求
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response,
            Object handler) throws Exception {
        response.setCharacterEncoding("utf-8");
        String token = request.getParameter("token");
        ResponseData responseData = ResponseData.ok();
        //token不存在
        if(null != token) {
            Login login = JWT.unsign(token, Login.class);
            String loginId = request.getParameter("loginId");
            //解密token后的loginId与用户传来的loginId不一致，一般都是token过期
            if(null != loginId && null != login) {
                if(Integer.parseInt(loginId) == login.getId()) {
                    return true;
                }
                else{
                    responseData = ResponseData.forbidden();
                    responseMessage(response, response.getWriter(), responseData);
                    return false;
                }
            }
            else
            {
                responseData = ResponseData.forbidden();
                responseMessage(response, response.getWriter(), responseData);
                return false;
            }
        }
        else
        {
            responseData = ResponseData.forbidden();
            responseMessage(response, response.getWriter(), responseData);
            return false;
        }
    }

    //请求不通过，返回错误信息给客户端
    private void responseMessage(HttpServletResponse response, PrintWriter out, ResponseData responseData) {
        responseData = ResponseData.forbidden();
        response.setContentType("application/json; charset=utf-8");
        String json = JSONObject.toJSONString(responseData);
        out.print(json);
        out.flush();
        out.close();
    }

}

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6.注意点：用@ResponseBody返回json数据时，有时会有乱码，需要在springmvc的配置文件里面加以下配置（spring4以上）

<mvc:annotation-driven>
     <mvc:message-converters register-defaults="true">
    <bean class="org.springframework.http.converter.StringHttpMessageConverter">
      <property name="supportedMediaTypes" value = "text/plain;charset=UTF-8" />
    </bean>
   </mvc:message-converters>
     </mvc:annotation-driven>  

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7.最后分享一个类，用于返回给客户端的万能类，我觉得它可以满足一般的接口

import java.util.HashMap;
import java.util.Map;

public class ResponseData {

    private final String message;
    private final int code;
    private final Map<String, Object> data = new HashMap<String, Object>();

    public String getMessage() {
        return message;
    }

    public int getCode() {
        return code;
    }

    public Map<String, Object> getData() {
        return data;
    }

    public ResponseData putDataValue(String key, Object value) {
        data.put(key, value);
        return this;
    }

    private ResponseData(int code, String message) {
        this.code = code;
        this.message = message;
    }

    public static ResponseData ok() {
        return new ResponseData(200, "Ok");
    }

    public static ResponseData notFound() {
        return new ResponseData(404, "Not Found");
    }

    public static ResponseData badRequest() {
        return new ResponseData(400, "Bad Request");
    }

    public static ResponseData forbidden() {
        return new ResponseData(403, "Forbidden");
    }

    public static ResponseData unauthorized() {
        return new ResponseData(401, "unauthorized");
    }

    public static ResponseData serverInternalError() {
        return new ResponseData(500, "Server Internal Error");
    }

    public static ResponseData customerError() {
        return new ResponseData(1001, "customer Error");
    }
}