今天前端說，返回給前端太多的null，會導致app閃退。

找的解決方案，作如下配置：我們專案用的是spring-boot。

第一種：當返回前端null的時候，便不再返回該欄位

（1）在bean上面加註解

import com.fasterxml.jackson.annotation.JsonInclude;
@JsonInclude(JsonInclude.Include.NON_NULL)

（2）在配置檔案中加註解

spring:
    jackson:
        default-property-inclusion: non_null

第二種：當需要返回null的時候，返回“”

package com.dingyi.configuration;

import com.alibaba.fastjson.serializer.SerializeConfig;
import com.alibaba.fastjson.serializer.SerializerFeature;
import com.alibaba.fastjson.serializer.ToStringSerializer;
import com.alibaba.fastjson.serializer.ValueFilter;
import com.alibaba.fastjson.support.config.FastJsonConfig;
import com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.MediaType;

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

/**
 * fastjson配置類
 *
 * @author fengshuonan
 * @date 2017-05-23 22:56
 */
@Configuration("defaultFastjsonConfig")
@ConditionalOnClass(com.alibaba.fastjson.JSON.class)
@ConditionalOnMissingBean(FastJsonHttpMessageConverter.class)
@ConditionalOnWebApplication
public class DefaultFastjsonConfig {

    @Bean
    public FastJsonHttpMessageConverter fastJsonHttpMessageConverter() {
        FastJsonHttpMessageConverter converter = new FastJsonHttpMessageConverter();
        converter.setFastJsonConfig(fastjsonConfig());
        converter.setSupportedMediaTypes(getSupportedMediaType());
        return converter;
    }

    /**
     * fastjson的配置
     */
    private FastJsonConfig fastjsonConfig() {
        FastJsonConfig fastJsonConfig = new FastJsonConfig();
        fastJsonConfig.setSerializerFeatures(
                SerializerFeature.DisableCircularReferenceDetect,
                SerializerFeature.PrettyFormat,
                SerializerFeature.WriteNullListAsEmpty,
                SerializerFeature.WriteNullStringAsEmpty,
                SerializerFeature.WriteMapNullValue,
                SerializerFeature.WriteNullBooleanAsFalse,
                SerializerFeature.WriteEnumUsingToString
        );
        fastJsonConfig.setDateFormat("yyyy-MM-dd HH:mm:ss");
        ValueFilter valueFilter = (o, s, o1) -> {
            if (null == o1) {
                o1 = "";
            }
            return o1;
        };

        fastJsonConfig.setCharset(Charset.forName("utf-8"));
        fastJsonConfig.setSerializeFilters(valueFilter);

        //解決Long轉json精度丟失的問題
        SerializeConfig serializeConfig = SerializeConfig.globalInstance;
        serializeConfig.put(BigInteger.class, ToStringSerializer.instance);
        serializeConfig.put(Long.class, ToStringSerializer.instance);
        serializeConfig.put(Long.TYPE, ToStringSerializer.instance);
        fastJsonConfig.setSerializeConfig(serializeConfig);
        return fastJsonConfig;
    }

    /**
     * 支援的mediaType型別
     */
    private List<MediaType> getSupportedMediaType() {
        ArrayList<MediaType> mediaTypes = new ArrayList<>();
        mediaTypes.add(MediaType.APPLICATION_JSON_UTF8);
        return mediaTypes;
    }
}