HandlerMethodArgumentResolver  是什么？

就是用于解析参数的一个接口，springMVC（4.1）会直接调用这个接口的方法，对参数进行一定的解析。比如会在 

InvocableHandlerMethod.getMethodArgumentValues（）中调用，并解析方法参数。 
具体如图：

然后就会根据这个resolver的规则进行参数的解析。

如何实现？
下面我们可以自定义一个resolver并实现：

具体实现：

1.@CurrentUser

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

    /**
     * 当前用户在request中的名字
     *
     * @return
     */
    String value() default "user";

}

2.CurrentUserMethodArgumentResolver

package com.spring.custom_anno;

import org.springframework.core.MethodParameter;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.ModelAndViewContainer;

@Component
public class CurrentUserMethodArgumentResolver implements HandlerMethodArgumentResolver {

    public CurrentUserMethodArgumentResolver() {
    }

    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        if (parameter.getParameterType().isAssignableFrom(UserBean.class) && parameter.hasParameterAnnotation(CurrentUser.class)) {
            return true;
        }
        return false;
    }

    @Override
    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
        CurrentUser currentUserAnnotation = parameter.getParameterAnnotation(CurrentUser.class);
        //从Session 获取用户
        Object object = webRequest.getAttribute(currentUserAnnotation.value(), NativeWebRequest.SCOPE_SESSION);
//从  accessToken获得用户信息
        if (object == null) {
            String token = webRequest.getHeader("Authorization");
            if (token == null) {
                token = webRequest.getParameter("accessToken");
            }
            //为了测试先写死用户名
            //TODO: 取真实用户
            return new UserBean(1L,"admin");
        }
        return object;
    }
}

3.UserBean

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.io.Serializable;

@Data
@NoArgsConstructor
@AllArgsConstructor
public class UserBean implements Serializable {
    private Long id;
    private String username;
}

4.Controller

import org.springframework.web.bind.annotation.*;

@RestController
public class TestController {
    @RequestMapping(value = "/testCurrentUser", method = RequestMethod.POST, produces = "application/json", consumes = "application/json")
    public void test(@CurrentUser UserBean userBean) {
        String createdBy = userBean.getUsername();
        System.out.println(createdBy);
    }
}

5.配置

1.（在XML中自定义传统项目做法，注意 自动扫描一定要放在resolver配置的下面才能生效。。实践过）

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
        xmlns:mvc="ht