SpringMVC3.1 引入了 HandlerMethodArgumentResolver 接口，Spring 调用该接口实现 Controller 的参数装配。HandlerMethodArgumentResolver 实现类中会调用 DataBinder，Converter 等。

由于之前用 @RequestParam 无法接受 request payload 正文格式为 json 格式的字符串，只能使用 @RequestBody 整个接收，觉得麻烦，但是 Spring 自带的参数解析器不具有这种功能，只能尝试着用自定义参数解析器去解决。

常用的该接口实现类有:

ServletModelAttributeMethodProcessor:实体类的组装用它实现。

RequestParamMethodArgumentResolver：基本数据类型如 String 用它实现。

自定义解析器需要实现 HandlerMethodArgumentResolver 接口，HandlerMethodArgumentResolver接口包含两个方法：

• supportsParameter：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。
• resolveArgument：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。

自定义注解

package com.manqian.crm.resolver;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;


@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
public @interface JsonParam {

    String value();

    boolean required() default true;

    String defaultValue() default "";
}

若不想自定义注解，可以直接在实现 HandlerMethodArgumentResolver 的 supportsParameter 直接返回 true。

自定义参数解析器

实现 HandlerMethodArgumentResolver 接口

import com.jayway.jsonpath.JsonPath;
import com.jayway.jsonpath.PathNotFoundException;
import com.manqian.crm.api.exception.ParamCheckException;
import org.apache.commons.io.IOUtils;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.MethodParameter;
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;

import javax.servlet.http.HttpServletRequest;
import java.io.IOException;

public class JsonPathArgumentResolver implements HandlerMethodArgumentResolver {

    private static final String JSON_REQUEST_BODY = "JSON_REQUEST_BODY";

    //判断是否支持要转换的参数类型
    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        return parameter.hasParameterAnnotation(JsonParam.class);
    }

    //当支持后进行相应的转换
    @Override
    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
        String body = getRequestBody(webRequest);
        Object val = null;

        try {
            val = JsonPath.read(body, parameter.getParameterAnnotation(JsonParam.class).value());
            if (parameter.getParameterAnnotation(JsonParam.class).required() && val == null) {
                throw new ParamCheckException(parameter.getParameterAnnotation(JsonParam.class).value() + "不能为空");
            }
        } catch (PathNotFoundException exception) {
            System.out.println(exception.getStackTrace());
            if (parameter.getParameterAnnotation(JsonParam.class).required()) {
//                throw new ParamCheckException(parameter.getParameterAnnotation(JsonParam.class).value() + "不能为空");
                throw exception;
            }
        }
        return val;
    }

    private String getRequestBody(NativeWebRequest webRequest) {
        HttpServletRequest servletRequest = webRequest.getNativeRequest(HttpServletRequest.class);
        String jsonBody = (String) servletRequest.getAttribute(JSON_REQUEST_BODY);
        if (jsonBody == null) {
            try {
                jsonBody = IOUtils.toString(servletRequest.getInputStream());
                servletRequest.setAttribute(JSON_REQUEST_BODY, jsonBody);
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return jsonBody;
    }
}

注册自定义参数解析器

springboot方式

方式一：

import java.util.List;

import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport;

import com.demo.mvc.component.MultiPersonArgumentResolver;
import com.demo.mvc.component.PersonArgumentResolver;

@SpringBootApplication
public class WebMvcConfiguration extends WebMvcConfigurationSupport {

    @Override
    protected void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
        // 注册JsonPathArgumentResolver的参数分解器
        argumentResolvers.add(new JsonPathArgumentResolver());
    }
}

方式二：

import org.springframework.context.annotation.Configuration;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

import java.util.List;

@Configuration
public class ClientResourcesConfig extends WebMvcConfigurerAdapter {

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

在新版 Spring Boot 中已经将 WebMvcConfigurerAdapter 标记为过时，可参考方式三。也可以查看Spring Boot WebMvcConfigurerAdapte 方法已经过时解决方法。

方式三：

import org.springframework.context.annotation.Configuration;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

import java.util.List;

@Configuration
public class ClientResourcesConfig implements WebMvcConfigurer {

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

传统XML格式

方式一：

<mvc:annotation-driven>
      <mvc:argument-resolvers>
        <bean class="com.manqian.crm.resolver.JsonPathArgumentResolver"/>
      </mvc:argument-resolvers>
</mvc:annotation-driven>

方式二：

<bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter">
    <property name="jsonPathArgumentResolver">
          <bean class="com.manqian.crm.resolver.JsonPathArgumentResolver"/>
    </property>
</bean>

依赖

com.jayway.jsonpath
json-path

拓展实例：获取用户信息

import org.springframework.core.MethodParameter;
import org.springframework.lang.Nullable;
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;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

/**
 * @author yeskery
 * @date 2018/06/02
 */
@Component
public class UserArgumentResolver implements HandlerMethodArgumentResolver {
    @Override
    public boolean supportsParameter(MethodParameter methodParameter) {
        if (methodParameter.getParameterType() == User.class) {
            return true;
        }
        return false;
    }

    @Nullable
    @Override
    public Object resolveArgument(MethodParameter methodParameter, @Nullable ModelAndViewContainer modelAndViewContainer, NativeWebRequest nativeWebRequest, @Nullable WebDataBinderFactory webDataBinderFactory) throws Exception {
        HttpServletRequest  request = nativeWebRequest.getNativeRequest(HttpServletRequest.class);
        HttpSession session = request.getSession();
        Object user = session.getAttribute("user");
        return user;
    }
}

本文部分内容来自：https://blog.csdn.net/u010187242/article/details/73647670