springboot處理返回值中的null為空字符串

package com.drink.sell.configuration;

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializerProvider;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;

import java.io.IOException;

@Configuration
public class JsonConfig {
    @Bean
    @Primary
    @ConditionalOnMissingBean(ObjectMapper.class)
    public ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder)
    {
        ObjectMapper objectMapper = builder.createXmlMapper(false).build();

        // 通過該方法對mapper對象進行設置，所有序列化的對象都將按改規則進行系列化
        // Include.Include.ALWAYS 默認
        // Include.NON_DEFAULT 屬性為默認值不序列化
        // Include.NON_EMPTY 屬性為 空（""） 或者為 NULL 都不序列化，則返回的json是沒有這個字段的。這樣對移動端會更省流量
        // Include.NON_NULL 屬性為NULL 不序列化,就是為null的字段不參加序列化
        //objectMapper.setSerializationInclusion(Include.NON_EMPTY);
        // 字段保留，將null值轉為""
        objectMapper.getSerializerProvider().setNullValueSerializer(new JsonSerializer<Object>()
        {
            @Override
            public void serialize(Object o, JsonGenerator jsonGenerator,
                                  SerializerProvider serializerProvider)
                    throws IOException, JsonProcessingException
            {
                jsonGenerator.writeString("");
            }
        });
        return objectMapper;
    }
}