SpringMVC参数解析ArgumentResolver（三）

测试

准备测试环境

SimpleController.java

@RestController
public class SimpleController {

    @ModelAttribute("nickname")
    public String init(Model model) {
        System.out.println("Controller: SimpleController init 执行");
        model.addAttribute("postCode", "225431");
        return "Rick";
    }

    @GetMapping("request")
    public Map<String, Object> request(@Validated User user,
                                   BindingResult bindingResult, //必须紧跟@Valid/@Validated对象后面
                                   @RequestParam(required = false) @Validated @Min(18) Integer age,
                                   @RequestParam Map<String, Object> requestParamMap,
                                   @RequestParam("names") List<String> namesList,
                                   String[] names,
                                   @ModelAttribute("postCode") String postCode,
                                   @ModelAttribute("nickname") String nickname,
                                   Map<String, Object> modelMap,
                                   Model model,
                                   HttpServletRequest request) {
        System.out.println("Controller: request 执行");

        Map<String, Object> resultMap = new HashMap<>();

        resultMap.put("requestParamMap", requestParamMap);
        resultMap.put("namesList", namesList);
        resultMap.put("names", names);

        resultMap.put("user", user);

        resultMap.put("age", age);
        resultMap.put("postCode", postCode);
        resultMap.put("nickname", nickname);
        resultMap.put("bindingResult", bindingResult.getAllErrors());

        modelMap.put("hobby", "swimming");
        model.addAttribute("sex", "男");
        request.setAttribute("home", "TaiXing");
        return resultMap;
    }
}
  • 请求
http://localhost:8080/request?age=1&names=Jim,Tom&name=Rick
  • 返回
{
    "names": ["Jim", "Tom"],
    "bindingResult": [],
    "namesList": ["Jim", "Tom"],
    "nickname": "Rick",
    "postCode": "225431",
    "requestParamMap": {
        "age": "1",
        "names": "Jim,Tom",
        "name": "Rick"
    },
    "user": {
        "age": 1,
        "name": "Rick"
    },
    "age": 1
}

分析

  • @ModelAttribute 写在方法上，返回值就是model的value，init在每次请求都会执行。init中有2个model属性 nickname postCode ，值分别是“Rick”“225432”
  • 对象 User 前面加了@Valid/@Validated 解析器 ModelAttributeMethodProcessor 会进行字段的验证。如果要收集异常，那么后面紧跟BindingResult。如果没有紧跟，那么如果验证失败将会抛出异常 BindException。
    源代码查看ModelAttributeMethodProcessor => validateIfApplicable(binder, parameter)
    => Object[] validationHints = ValidationAnnotationUtils.determineValidationHints(ann);
  • age 使用 RequestParamMethodArgumentResolver 解析，解析后对字段类型由String转换成Integer，该解析器不支持验证，所以虽然加了“@Validated @Min(18)”但是并不会验证
  • requestParamMap 将所有的请求参数值放到requestParamMap中，如果参数是数组，只放第一个
  • namesList 和 names 是“简单类型” 由RequestParamMethodArgumentResolver 解析，解析后对字段类型由String转换成对应的类型
  • postCode 和 nickname 参数使用注解 @ModelAttribute 表示从model中获取值，这里@ModelAttribute的属性name不要省略
  • model 使用解析器 ModelMethodProcessor；modelMap 使用解析器 MapMethodProcessor。modelMap 和 model 是同一个引用。 视图解析器比如ThymeleafView会将model中的值放入request scope中
  • request 使用 ServletRequestMethodArgumentResolver 进行解析

自定义参数解析器

系统提供了很多默认的参数处理器

0 = {RequestParamMethodArgumentResolver@8604} 
1 = {RequestParamMapMethodArgumentResolver@8605} 
2 = {PathVariableMethodArgumentResolver@8606} 
3 = {PathVariableMapMethodArgumentResolver@8607} 
4 = {MatrixVariableMethodArgumentResolver@8608} 
5 = {MatrixVariableMapMethodArgumentResolver@8609} 
6 = {ServletModelAttributeMethodProcessor@8610} 
7 = {RequestResponseBodyMethodProcessor@8611} 
8 = {RequestPartMethodArgumentResolver@8612} 
9 = {RequestHeaderMethodArgumentResolver@8613} 
10 = {RequestHeaderMapMethodArgumentResolver@8614} 
11 = {ServletCookieValueMethodArgumentResolver@8615} 
12 = {ExpressionValueMethodArgumentResolver@8616} 
13 = {SessionAttributeMethodArgumentResolver@8617} 
14 = {RequestAttributeMethodArgumentResolver@8618} 
15 = {ServletRequestMethodArgumentResolver@8619} 
16 = {ServletResponseMethodArgumentResolver@8620} 
17 = {HttpEntityMethodProcessor@8621} 
18 = {RedirectAttributesMethodArgumentResolver@8622} 
19 = {ModelMethodProcessor@8623} 
20 = {MapMethodProcessor@8624} 
21 = {ErrorsMethodArgumentResolver@8625} 
22 = {SessionStatusMethodArgumentResolver@8626} 
23 = {UriComponentsBuilderMethodArgumentResolver@8627} 
24 = {PrincipalMethodArgumentResolver@8629} 
25 = {RequestParamMethodArgumentResolver@8630} 
26 = {ServletModelAttributeMethodProcessor@8631} 


@Configuration
public class WebMvcConfig implements WebMvcConfigurer {
    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers) {
        resolvers.add(new HandlerMethodArgumentResolver() {

            @Override
            public boolean supportsParameter(MethodParameter parameter) {
                return User.class == parameter.getParameterType();
            }

            @Override
            public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
                User user = new User();
                user.setName("Green");
                user.setAge(92);
                return user;
            }
        });
    }
}

这个参数解析器会在 ServletModelAttributeMethodProcessor 之前执行，非简单对象会先使用自定义的解析器解析。自定义的参数解析器的应用场景，我们可以根据token解析出用户信息放入参数中

GitHub:https://github.com/jkxyx205/spring-boot-learn/tree/master/spring-mvc-argument-resolver