HandlerMethodArgumentResolver与HandlerMethodReturnValueHandler

转载自：
　　https://blog.youkuaiyun.com/nnsword/article/details/76260355
　　https://blog.youkuaiyun.com/Rylan11/article/details/79433192

HandlerMethodArgumentResolver是用来为处理器解析参数的，主要用在HandlerMethod中，每个Resolver对应一种类型的参数。

public interface HandlerMethodArgumentResolver {
    // 用于判断是否支持对某种参数的解析
    boolean supportsParameter(MethodParameter parameter);

    // 将请求中的参数值解析为某种对象
    @Nullable
    Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
            NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception;

}

示例：

public class UserMethodArgumentResolver implements HandlerMethodArgumentResolver {
    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        if(parameter.getParameterType() != null
                && parameter.getParameterType().equals(User.class)){
            return true;
        }else {
            return false;
        }

    }

    @Override
    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
        Authentication authentication = SecurityContextHolder.getContext()
                .getAuthentication();
        if (authentication == null) {
            return null;
        }
        Object principal = authentication.getPrincipal();
        if (principal != null
                && !parameter.getParameterType().isAssignableFrom(User.class)) {
            User userDetails = (User)principal;
            return userDetails;
        }
        return principal;
    }
}

@Configuration
public class WebParameterConfig extends WebMvcConfigurerAdapter {

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

@RequestMapping("/"+IndexController.Mapping_Url)
@Controller
public class IndexController {
    public static final String Mapping_Url="manage";

    @RequestMapping(value = {"/",""})
    public String index(Model model, Authentication authentication,User user){
        model.addAttribute("title","userweb");
        //输出登录提示信息
        //System.out.println("管理员 " + user.getUsername() + " 进入");
        return Mapping_Url+"/index";
    }
}

---

HandlerMethodReturnValueHandler是RequestMappingHandlerAdapter用来处理完映射控制类，对方法返回的值进一步进行处理。

public interface HandlerMethodReturnValueHandler {

    /**
     * 该处理程序是否支持给定的方法返回类型(只有返回true才回去调用handleReturnValue)
     */
    boolean supportsReturnType(MethodParameter returnType);

    /**
     * 处理给定的返回值
     * 通过向 ModelAndViewContainer 添加属性和设置视图或者
     * 通过调用 ModelAndViewContainer.setRequestHandled(true) 来标识响应已经被直接处理(不再调用视图解析器)
     */
    void handleReturnValue(Object returnValue, MethodParameter returnType,
            ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception;

}

示例：

public class MyHandlerMethodReturnValueHandler implements HandlerMethodReturnValueHandler {
    @Override
    public boolean supportsReturnType(MethodParameter returnType) {
        return returnType.getParameterType() == Person.class;
    }

    @Override
    public void handleReturnValue(Object returnValue, MethodParameter returnType, ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
        Assert.isInstanceOf(Person.class, returnValue);

        //标识请求是否已经在该方法内完成处理
        mavContainer.setRequestHandled(true);

        // 获取方法上的注解
        PersonAnnotation personAnnotation = returnType.getMethodAnnotation(PersonAnnotation.class);

        HttpServletResponse response = webRequest.getNativeResponse(HttpServletResponse.class);
        response.setContentType("text/plain;charset=UTF-8");
        Person person = (Person) returnValue;
        response.getWriter().println(personAnnotation.value() + ":" + person);

    }
}

@Controller
public class DemoController {
    @PersonAnnotation("person")
    @RequestMapping(value = "/demo", method = RequestMethod.GET)
    public Person getPerson() {
        return new Person("xiya", 25);
    }
}

同样，在WebMvcConfigurerAdapter中，重写addReturnValueHandlers方法即可。