HandlerMethodArgumentResolver 自定义参数解析器

HandlerMethodArgumentResolver 接口详情

public interface HandlerMethodArgumentResolver {
 
    boolean supportsParameter(MethodParameter parameter);
    
    @Nullable
    Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
                           NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception;
    
}

supportsParameter 表示当前参数解析器能够处理什么样参数，当为true时才会执行resolveArgument方法。
resolveArgument 实参的具体处理方法。

应用场景

1. Spring中@RequestParam，@PathVariable，@RequestBody注解的解析器等等.
2. 可以通过自定义注解在参数列表中自动注入当前登录用户.
   
   

代码实现

3. 自定义注解

@Target({ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface CurrentUser {
}

4. 自定义参数解析，若参数中有我们自定义@CurrentUser注解时，将当前登录用户信息保存至其中

@Componetn
public class CurrentUserMethodArgumentResolver implements HandlerMethodArgumentResolver {

    @Resource
    private RedisUtils redisUtils;

    public boolean supportsParameter(MethodParameter parameter) {
        // 当参数中使用了我们的自定义注解的时候
        if (parameter.hasParameterAnnotation(CurrentUser.class)) {
            return true;
        }
        return false;
    }

    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
        String token = httpServletRequest.getHeader("token");
        if(token == null){
        	throw new CustomException(ResultStatus.ERROR.getCode(), "token不能为空");
        }
        Object obj = redisUtils.get(token);
        if(obj == null){
        	throw new CustomException(ResultStatus.ERROR.getCode(), "token失效");
        }
        return (SysUser)obj;
    }
}

5. 将参数解析器添加至Application容器中

@Configuration
public class ApplicationConfigurer extends WebMvcConfigurerAdapter {
    
    @Resource
    private CurrentUserMethodArgumentResolver currentUserMethodArgumentResolver;
    
    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
        super.addArgumentResolvers(argumentResolvers);
        argumentResolvers.add(currentUserMethodArgumentResolver);
    }
}

6. 控制层可以通过@CurrentUser注解来实现当前登录用户信息自动解析注入

@RequestMapping("/list")
public ResultInfo<?> list(@CurrentUser SysUser sysUser,String name){
 	// sysUser 就是当前登录用户的信息   
}