在專案開發中，我們會遇到一些null值。如果不想讓返回資料有null值，而是返回空字串該怎麼辦捏。

So Easy！！！

我們做一下配置就好了。

1.Jackson  null值處理：spring-boot是對Jackson預設支援的，所以有了web的依賴則不需要引入依賴了。

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 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;

/**
 * 描述: 處理資料返回的null值
 * @author Administrator
 * @create 2018-10-18 14:51
 */
@Configuration
public class JacksonConfig {
    @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;
    }
}
 

2.fastjson null值處理

 2.1：需要引入fastjson 依賴

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.2.35</version>
</dependency>

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.WebMvcConfigurationSupport;

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

@Configuration
public class fastJsonConfig extends WebMvcConfigurationSupport {

    /**
     * 使用阿里 fastjson 作為JSON MessageConverter
     * @param converters
     */
    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        FastJsonHttpMessageConverter converter = new FastJsonHttpMessageConverter();
        FastJsonConfig config = new FastJsonConfig();
        config.setSerializerFeatures(
                // 保留map空的欄位
                SerializerFeature.WriteMapNullValue,
                // 將String型別的null轉成""
                SerializerFeature.WriteNullStringAsEmpty,
                // 將Number型別的null轉成0
                SerializerFeature.WriteNullNumberAsZero,
                // 將List型別的null轉成[]
                SerializerFeature.WriteNullListAsEmpty,
                // 將Boolean型別的null轉成false
                SerializerFeature.WriteNullBooleanAsFalse,
                // 避免迴圈引用
                SerializerFeature.DisableCircularReferenceDetect);

        converter.setFastJsonConfig(config);
        converter.setDefaultCharset(Charset.forName("UTF-8"));
        List<MediaType> mediaTypeList = new ArrayList<>();
        // 解決中文亂碼問題，相當於在Controller上的@RequestMapping中加了個屬性produces = "application/json"
        mediaTypeList.add(MediaType.APPLICATION_JSON);
        converter.setSupportedMediaTypes(mediaTypeList);
        converters.add(converter);
    }
}
 

ok，這樣就可以將返回資料中的null值轉為空字串了。