SpringMVC传递json字符串，后台接口通过变量接收

前景介绍

在我们日常开发过程中，前台向后台传递参数一般是json 或者 form表单方式，并且最好统一一种传输方式，不建议json+form混合使用，但是由于form表单在数组结构下拼接比较麻烦，一般都采用的json去传递，后端采用SpringBoot(SpringMVC)一般使用@RequestBody注解去接收数据，但如下情况不太好处理

@RequestMapping("/login")
public String login(String name,String password){
	....
}
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以上方法如果去接收json对象是无法映射的，由于字段太少封装成对象+@RequestBody又太过于繁琐， 这种情况我们可以使用自定义注解+方法参数解析器去解决这个问题

一.导入相关依赖

框架中是用的hutool工具包，根据自己项目情况使用json序列化工具

<dependency>
            <groupId>cn.hutool</groupId>
            <artifactId>hutool-all</artifactId>
            <version>5.7.6</version>
        </dependency>
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二.定义注解

通过自定义注解标注在需要做数据映射的参数上

@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface JSONParameter {
    @AliasFor("name")
    String value() default "";

    @AliasFor("value")
    String name() default "";

    boolean required() default false;

    String defaultValue() default "";
}


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三.编写自定义参数解析器

package com.gosun.swd.commom.resolver;

import cn.hutool.json.JSONArray;
import cn.hutool.json.JSONObject;
import cn.hutool.json.JSONUtil;
import com.gosun.swd.commom.annotation.JSONParameter;
import com.gosun.swd.commom.exception.Assert;
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.context.request.RequestContextHolder;
import org.springframework.web.context.request.ServletRequestAttributes;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.ModelAndViewContainer;
import sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl;

import javax.servlet.http.HttpServletRequest;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Type;
import java.util.List;
import java.util.Set;

@Component
public class JSONParameterResolver implements HandlerMethodArgumentResolver {

//    ThreadLocal<JSONObject> paramObject = new ThreadLocal<>();


    @Override
    public boolean supportsParameter(MethodParameter methodParameter) {
        return methodParameter.hasParameterAnnotation(JSONParameter.class);
    }

    @Override
    public Object resolveArgument(MethodParameter methodParameter, ModelAndViewContainer modelAndViewContainer, NativeWebRequest nativeWebRequest, WebDataBinderFactory webDataBinderFactory) throws Exception {
        JSONObject jsonObject = getJsonObject();
        Object o = jsonObject.get(methodParameter.getParameterName());
        JSONParameter parameterAnnotation = methodParameter.getParameterAnnotation(JSONParameter.class);
        //判断是否允许为空
        String message = String.format("参数%s不能为空", methodParameter.getParameterName());
        Assert.assertFalse(parameterAnnotation.required() && o == null, message);
        //如果为空设置默认值
        if (o == null) {
            return convertParameter(methodParameter, parameterAnnotation.defaultValue());
        }
        return convertParameter(methodParameter, o);
    }

    private Object convertParameter(MethodParameter methodParameter, Object o) throws ClassNotFoundException, InstantiationException, IllegalAccessException, InvocationTargetException {
        if (methodParameter.getParameterType().getTypeName().equals(List.class.getTypeName()) ||
                methodParameter.getParameterType().getTypeName().equals(Set.class.getTypeName())) {
            Type actualTypeArgument = ((ParameterizedTypeImpl) methodParameter.getGenericParameterType()).getActualTypeArguments()[0];
            return JSONUtil.toList((JSONArray) o, Class.forName(actualTypeArgument.getTypeName()));
        } else {
            return convertParameter(methodParameter, String.valueOf(o));
        }
    }

    private Object convertParameter(MethodParameter methodParameter, String obj) throws InstantiationException, IllegalAccessException, InvocationTargetException {
        Constructor<?>[] constructors = methodParameter.getParameterType().getConstructors();
        for (Constructor<?> constructor : constructors) {
            if (constructor.getParameterCount() == 1 && constructor.getParameters()[0].getParameterizedType().getTypeName().equals(String.class.getTypeName())) {
                return constructor.newInstance(obj);
            }
        }
        return null;
    }

    private JSONObject getJsonObject() throws IOException {
        HttpServletRequest request = ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes()).getRequest();
        BufferedReader streamReader = new BufferedReader(new InputStreamReader(request.getInputStream(), "UTF-8"));
        StringBuilder responseStrBuilder = new StringBuilder();
        String inputStr;
        while ((inputStr = streamReader.readLine()) != null) {
            responseStrBuilder.append(inputStr);
        }
        String jsonStr = responseStrBuilder.toString();
//        if (StringUtils.isEmpty(jsonStr)) {//如果没有参数，表示不是第一次进入
//            return paramObject.get() == null ? new JSONObject() : paramObject.get();
//        }
        JSONObject jsonObject = JSONUtil.parseObj(jsonStr);
//        paramObject.set(jsonObject);
        return jsonObject;
    }
}

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四.解决二次获取request信息丢失的问题

1.编写过滤器

package com.gosun.swd.commom.resolver;


import org.springframework.stereotype.Component;

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;

/**
 * @author:
 */
@Component
@WebFilter(filterName = "channelFilter", urlPatterns = {"/*"})
public class ChannelFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) {
        try {
            ServletRequest requestWrapper = null;
            if (request instanceof HttpServletRequest) {
                requestWrapper = new RequestWrapper((HttpServletRequest) request);
            }
            if (requestWrapper == null) {
                chain.doFilter(request, response);
            } else {
                chain.doFilter(requestWrapper, response);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ServletException e) {
            e.printStackTrace();
        }


    }

    @Override
    public void destroy() {
    }

}
 
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2.编写构造器

package com.gosun.swd.commom.resolver;

import org.apache.commons.io.IOUtils;

import javax.servlet.ReadListener;
import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import java.io.*;

/**
 * @author:
 */
public class RequestWrapper extends HttpServletRequestWrapper {
    //参数字节数组
    private byte[] requestBody;
    //Http请求对象
    private HttpServletRequest request;

    public RequestWrapper(HttpServletRequest request) throws IOException {
        super(request);
        this.request = request;
    }

    /**
     * @return
     * @throws IOException
     */
    @Override
    public ServletInputStream getInputStream() throws IOException {
        /**
         * 每次调用此方法时将数据流中的数据读取出来，然后再回填到InputStream之中
         * 解决通过@RequestBody和@RequestParam(POST方式)读取一次后控制器拿不到参数问题
         */
        if (null == this.requestBody) {
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            IOUtils.copy(request.getInputStream(), baos);
            this.requestBody = baos.toByteArray();
        }

        final ByteArrayInputStream bais = new ByteArrayInputStream(requestBody);
        return new ServletInputStream() {

            @Override
            public boolean isFinished() {
                return false;
            }

            @Override
            public boolean isReady() {
                return false;
            }

            @Override
            public void setReadListener(ReadListener listener) {

            }

            @Override
            public int read() {
                return bais.read();
            }
        };
    }

    public byte[] getRequestBody() {
        return requestBody;
    }

    @Override
    public BufferedReader getReader() throws IOException {
        return new BufferedReader(new InputStreamReader(this.getInputStream()));
    }
}
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五.调用实例代码

@RequestMapping("/login")
	public String login(@JSONParameter String name, @JSONParameter String password){
	....
	}

	//包含默认值的参数映射
    @PostMapping(value = "/getEvents", consumes = "application/json")
    public ResultVo<Events> getEvents(@JSONParameter(name = "page", defaultValue = "1") Long page, 
                                      @RequestParam(name = "per_page", defaultValue = "10") Long per_page, 
                                      @JSONParameter String type) {
	....
    }
    
    //字段集合
    @PostMapping(value = "/deleteCarInfo", consumes = "application/json")
    public ResultVo deleteCarInfo(@JSONParameter List<Long> ids) {
	....
    }
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来源：https://juejin.cn/post/7077811223395303460