参数解析器HandlerMethodArgumentResolver

HandlerMethodArgumentResolver的使用

在项目中可以用于快速获取指定对象，修改参数等

1.定义一个实体类Person

@Data
public class Person {
    private String firstName;
    private String lastName="notVa";

    public Person(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }
}

2.使用Controller获取这个Person

//前端传入属性firstName和lastName
@Controller
public class DemoHandlerMethodArgumentResolverController {

    @RequestMapping(value = "/demoAddPerson")
    @ResponseBody
    public String addPerson(Person person) {
        System.out.println(person.toString());
        return person.toString();
    }
}

3.可以自己定义参数解析的过程，先建立一个解析器

实现将传入的参数前面添加上new字符串（也可以改变返回的对象）

@Component
//实现HandlerMethodArgumentResolver接口
public class PersonArgumentResolver implements HandlerMethodArgumentResolver {
    @Override
    public boolean supportsParameter(MethodParameter methodParameter) {
        return methodParameter.getParameterType().equals(Person.class);
    }

    @Override
    public Object resolveArgument(MethodParameter methodParameter, ModelAndViewContainer modelAndViewContainer, NativeWebRequest nativeWebRequest, WebDataBinderFactory webDataBinderFactory) throws Exception {
        HttpServletRequest request = nativeWebRequest.getNativeRequest(HttpServletRequest.class);
        String firstName = request.getParameter("firstName");
        String lastName = request.getParameter("lastName");
        return new Person("new"+firstName,"new"+lastName);
    }
}

//接口说明
public interface HandlerMethodArgumentResolver {
    //用于判定是否需要处理该参数分解，返回true为需要，并会去调用下面的方法resolveArgument。
    boolean supportsParameter(MethodParameter parameter);
    //真正用于处理参数分解的方法，返回的Object就是controller方法上的形参对象。
    Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
            NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception;

}

4.注册这个解析器

//继承WebMvcConfigurationSupport类，实现方法
@Configuration
public class ConfigArgumentResolver extends WebMvcConfigurationSupport {
    @Autowired
    private PersonArgumentResolver personArgumentResolver;

    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
        argumentResolvers.add(personArgumentResolver);
    }
}

5.测试效果

输入 http://localhost:8080/demoAddPerson?firstName=fi&lastName=la

返回 Person(firstName=newfi, lastName=newla)

多个Person

1.添加一个注解

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.PARAMETER)
public @interface MultiPerson {
    String value();
}

2.解析器

@Component
public class MultiPersonArgumentResolver implements HandlerMethodArgumentResolver {
    @Override
    public boolean supportsParameter(MethodParameter methodParameter) {
        return methodParameter.hasParameterAnnotation(MultiPerson.class) && methodParameter.getParameterType().equals(Person.class);
    }

    @Override
    public Object resolveArgument(MethodParameter methodParameter, ModelAndViewContainer modelAndViewContainer, NativeWebRequest nativeWebRequest, WebDataBinderFactory webDataBinderFactory) throws Exception {
        HttpServletRequest request = nativeWebRequest.getNativeRequest(HttpServletRequest.class);
        MultiPerson multiPerson = methodParameter.getParameterAnnotation(MultiPerson.class);
        String firstName = multiPerson.value()+"."+ request.getParameter("firstName");
        String lastName = multiPerson.value()+"."+ request.getParameter("lastName");
        return new Person(firstName,lastName);
    }
}

3.注册

@Configuration
public class ConfigArgumentResolver extends WebMvcConfigurationSupport {
    @Autowired
    private PersonArgumentResolver personArgumentResolver;

    @Autowired
    private MultiPersonArgumentResolver multiPersonArgumentResolver;

    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
        //argumentResolvers.add(personArgumentResolver);
        argumentResolvers.add(multiPersonArgumentResolver);

    }
}

4.Controller

@RequestMapping(value = "/demoAddMultiPerson")
    @ResponseBody
    public String addMultiPerson(@MultiPerson("person1") Person person1,@MultiPerson("person2")Person person2) {
        System.out.println(person1.toString());
        System.out.println(person2.toString());
        return person1.toString()+" --- "+ person2.toString();
    }

5.测试效果

输入 http://localhost:8080/demoAddMultiPerson?firstName=fi&lastName=la

结果 Person(firstName=person1.fi, lastName=person1.la) ---- Person(firstName=person2.fi, lastName=person2.la)