# 1. 使用自定义参数注解获取 token 中User数据

## 使用背景

在springboot项目开发中需要从token中获取用户信息时通常的方式要经历几个步骤

1. 拦截器中截获token
2. TokenUtil工具类解析token中的用户信息
3. 把解析结果存入到成员变量中
4. controller中通过TokenUtil工具类提供的静态方法获取用户信息

下面是过程示例代码

```java
/*--------1.拦截器中获取---------*/
String token =request.getHeader("token")

/*--------2.解析---------*/
//如果没过期且有效
if(!TokenUtil.isExpire(token)){
    //解析token把结果存入成员变量
    TokenUtil.decode(token);
}

/*--------3.controller中获取---------*/
User currentUser=TokenUtil.getUser();
```

看上去也没什么复杂指处,但是如果在每个Controller中都加上一句 `User currentUser=TokenUtil.getUser();`感觉有些多余(潜意识知道肯定有更简洁的方法能减少这里所写代码)

下面介绍一种使用自定义参数注解的方法简化获取结果

## 最后预期达到的效果

```java
@{RequestMethod}Mapping(value="path")
public Object methodName(@CurrentUser User user){
    //...code
}
```

## 正文开始

### 1. 拦截器中的代码(GlobalInterceptor.java)

```java
public class GlobalInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        String token=request.getHeader("token");
        //判断路径需要拦截
        //....code

        //如果token有效
        if(!TokenUtil.isExpire(token)){
            User user = TokenUtil.getUser(token);
            //我们将解析的用户结果先放入session中
            request.getSession().setAttribut("currentUser",user);
        }

        return true;
    }
}
```

### 2. 注解类 (CurrentUser.java)

```java
@Target({ElementType.PARAMETER})//Annotation所修饰的对象范围:方法参数
@Retention(RetentionPolicy.RUNTIME)//Annotation被保留时间:运行时保留(有效)
@Documented//标记注解:java工具文档化
public @interface CurrentUser {

}
```

### 3. CurrentUser注解实现类(CurrentUserHandlerMethodArgReslover.java)

```java
public class CurrentUserHandlerMethodArgReslover implements HandlerMethodArgumentResolver {

    /**
    * 判断是否支持使用@CurrentUser注解的参数
    */
    @Override
    public boolean supportsParameter(MethodParameter methodParameter) {
        //如果该参数注解有@CurrentUser且参数类型是User
        return methodParameter.getParameterAnnotation(CurrentUser.class) != null &&methodParameter.getParameterType() == User.class;
    }

    /**
    * 注入参数值
    */
    @Override
    public Object resolveArgument(MethodParameter methodParameter, ModelAndViewContainer modelAndViewContainer, NativeWebRequest nativeWebRequest, WebDataBinderFactory webDataBinderFactory) throws Exception {
        //取得HttpServletRequest
        HttpServletRequest request= (HttpServletRequest) nativeWebRequest.getNativeRequest();
        //取出session中的User
        return (User)request.getSession().getAttribute("currentUser");
    }
}
```

### 4. 在SpringBoot启动类中注册 注解的实现类与拦截器(ServerApplication.java)

```java
@SpringBootApplication
public class ServerApplication extends WebMvcConfigurationSupport {

    /**
     * 启动入口
     * @param args
     */
    public static void main(String[] args) {
        SpringApplication.run(ServerApplication.class,args);
    }

    @Override
    protected void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers){
        //注册@CurrentUser注解的实现类
        argumentResolvers.add(new CurrentUserHandlerMethodArgReslover());
    }

    /**
    * 注册拦截器
    * @param registry
    */
    @Override
    protected void addInterceptors(InterceptorRegistry registry {
        //注册拦截器
        registry.addInterceptor(new GlobalInterceptor().addPathPatterns("/*/api/**");
        registry.addInterceptor(new TestInterceptor().addPathPatterns("/*/api/test/**");
        super.addInterceptors(registry);
    }
}
```

### 5. 在Controller中使用

```java
@GetMapping(value="/demo/api/testget")
public Object getTest(@CurrentUser User currentUser){
    System.out.println(currentUser);
    return currentUser;
}
```

到此就实现了预期的结果,回头看发现虽然多写了不少代码,但是在用的时候还是更加简洁明了,美丽大方(给自己比个❤)


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