spring 自定参数解析器（HandlerMethodArgumentResolver）

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。

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

接口说明： 
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。

1、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

2、自定义参数解析器，实现HandlerMethodArgumentResolver接口

package com.manqian.crm.resolver;

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;

    }

}

3、注册自定义参数解析器 
springboot方式： 
1、

package com.demo;

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());
    }
}

2、

package com.manqian.crm.resolver;

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());
    }
}

传统XML格式： 
1、

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

2、

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

使用： 
1、依赖： 

com.jayway.jsonpath 
json-path 

2、controller方法使用@JsonParam接收参数