第一篇   JSON.toJSONString格式化成json字符串时保留null属性

原文：https://blog.csdn.net/qq_34412985/article/details/81985459

使用阿里的

com.alibaba.fastjson.JSON

格式化时，默认null属性会被过滤掉，可以设置不过滤null，参考作者的博文

public static String parseScriptJsonStringWithNullValue(Object obj) {

   if (obj == null || (obj instanceof Undefined)) {

      return null;

   }

   return JSON.toJSONString(obj, new SerializeFilter[]{scriptArrayFilter}, SerializerFeature.WriteMapNullValue);

}

指定这个参数即可

SerializerFeature.WriteMapNullValue

属性说明

QuoteFieldNames———-输出key时是否使用双引号,默认为true

WriteMapNullValue——–是否输出值为null的字段,默认为false

WriteNullNumberAsZero—-数值字段如果为null,输出为0,而非null

WriteNullListAsEmpty—–List字段如果为null,输出为[],而非null

WriteNullStringAsEmpty—字符类型字段如果为null,输出为”“,而非null

WriteNullBooleanAsFalse–Boolean字段如果为null,输出为false,而非null

例子：

String ret = JSON.toJSONStringWithDateFormat(returnValue, "yyyy-MM-dd HH:mm:ss",
                SerializerFeature.PrettyFormat,
                    // 保留map空的字段
                    SerializerFeature.WriteMapNullValue,
                    // 将String类型的null转成""
                    SerializerFeature.WriteNullStringAsEmpty,
                    // 将Number类型的null转成0
                    SerializerFeature.WriteNullNumberAsZero,
                    // 将List类型的null转成[]
                    SerializerFeature.WriteNullListAsEmpty,
                    // 将Boolean类型的null转成false
                    SerializerFeature.WriteNullBooleanAsFalse,
                    // 避免循环引用
                    SerializerFeature.DisableCircularReferenceDetect
                );

第二篇  springboot 处理返回结果中字段为空或为null，不展示字段的问题（字段展示不全）

package com.aiqin.mgs.market.api.config;

import com.alibaba.fastjson.serializer.SerializerFeature;
import com.alibaba.fastjson.support.config.FastJsonConfig;
import com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.MediaType;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport;

import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.List;

/**
 * description: fastjson处理返回的参数为null、或者不返回
 * date: 2019/11/22 15:03
 * author: hantao
 * version: 1.0
 * springboot 处理返回结果中字段为空或为null，不展示字段的问题（字段展示不全）
 */
@Configuration
public class FastJsonConfiguration extends WebMvcConfigurationSupport {

    /**
     * 使用阿里 fastjson 作为JSON MessageConverter
     * @param converters
     */
    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        FastJsonHttpMessageConverter converter = new FastJsonHttpMessageConverter();
        FastJsonConfig config = new FastJsonConfig();
        config.setSerializerFeatures(
                // 保留map空的字段
                SerializerFeature.WriteMapNullValue,
                // 将String类型的null转成""
                SerializerFeature.WriteNullStringAsEmpty,
                // 将Number类型的null转成0
                SerializerFeature.WriteNullNumberAsZero,
                // 将List类型的null转成[]
                SerializerFeature.WriteNullListAsEmpty,
                // 将Boolean类型的null转成false
                SerializerFeature.WriteNullBooleanAsFalse,
                // 避免循环引用
                SerializerFeature.DisableCircularReferenceDetect);

        converter.setFastJsonConfig(config);
        converter.setDefaultCharset(Charset.forName("UTF-8"));
        List<MediaType> mediaTypeList = new ArrayList<>();
        // 解决中文乱码问题，相当于在Controller上的@RequestMapping中加了个属性produces = "application/json"
        mediaTypeList.add(MediaType.APPLICATION_JSON);
        converter.setSupportedMediaTypes(mediaTypeList);
        converters.add(converter);
    }

    /**
     * 整合了swagger需要配置swagger拦截
     * @param registry
     */
    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        registry.addResourceHandler("swagger-ui.html","index.html").addResourceLocations("classpath:/META-INF/resources/");
        registry.addResourceHandler("doc.html").addResourceLocations("classpath:/META-INF/resources/");
        registry.addResourceHandler("/webjars/**").addResourceLocations("classpath:/META-INF/resources/webjars/");
        registry.addResourceHandler("/static/**").addResourceLocations("classpath:/META-INF/resources/static/");
    }

}