@[toc]

前言

本篇博客是SpringBoot统一处理null转为空，若文章中出现相关问题，请指出！

所有博客文件目录索引：博客目录索引(持续更新)

一、Jackson方式实现对null字段转为空字符串(springboot自带jackson)

springboot自带jackson，所以不需要额外引入坐标：

编写配置类：我的理解是实例化ObjectMapper对象交由spring管理，之后在使用jackson转化json字符串时执行

@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;
    }
}

二、fastjson方式实现

需要手动引入依赖fastjson：

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

编写配置类：较完整的配置

• 该种方式是实现springmvc中的WebMvcConfigurationSupport类重新其中的configureMessageConverters方法，添加一个转换器来对返回值内容进行转换。

@Configuration
public class fastJsonConfig 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);
    }
}

测试

上面两种方案都可行

我们编写两个类来进行测试：

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private Long id;
    private String name;
    private Integer age;
    private String email;
    private String address;
}

@RestController
@RequestMapping("/api/v1/test")
@Slf4j  //在类上添加该接口
public class UserController {

    @GetMapping("/{id}")
    public ResultBody test(@PathVariable(value = "id")Integer myid){
        ArrayList<User> users = new ArrayList<>(10);
        users.add(new User((long)111, "changlu", 11, null,null));
        users.add(new User((long)111, null, 11, null,null));
        users.add(new User((long)111, "changlu", 11, null,null));
        users.add(new User((long)111, null, 11, null,null));
        users.add(new User((long)111, "changlu", 11, null,null));
        users.add(new User((long)111, null, 11, null,null));
        users.add(new User((long)111, "changlu", 11, null,null));

        return ResultBody.success(users);
    }
}

转换成功！

参考文章

[1]. spring-boot返回数据为null时返回空字符串