springboot DTO返回数据为null时返回空字符串

一、不返回null值

在yml配置文件中添加如下配置即可
jackson:
default-property-inclusion: non_null

二、遇到null值时返回空字符串，代码如下

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.datatype.hibernate5.Hibernate5Module;
import com.fasterxml.jackson.module.afterburner.AfterburnerModule;
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 JacksonConfiguration {

    /**
     * Support for Hibernate types in Jackson.
     */
    @Bean
    public Hibernate5Module hibernate5Module() {
        return new Hibernate5Module();
    }

    /**
     * Jackson Afterburner module to speed up serialization/deserialization.
     */
    @Bean
    public AfterburnerModule afterburnerModule() {
        return new AfterburnerModule();
    }

    @Bean
    @Primary
    @ConditionalOnMissingBean(ObjectMapper.class)
    public ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder) {
        ObjectMapper objectMapper = builder.createXmlMapper(false).build();
        objectMapper.getSerializerProvider().setNullValueSerializer(new JsonSerializer<Object>() {
            @Override
            public void serialize(Object o, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
                jsonGenerator.writeString("");
            }
        });
        return objectMapper;
    }
}