[Java] Spring boot returns a field that is null and is filtered

foreword

Recently, due to project needs, I rebuilt a set of frameworks from scratch for colleagues to use. When the front-end and back-end are connected, it is found that the fields provided by the back-end are missing a lot, that is, the fields with entity classes with null values ​​are all filtered out. After investigation, it is the fault of fastjson.

Because fastjson filters out values ​​whose value is null by default, and does not output null values.

 

As the saying goes, when you encounter a problem, find the cause of the problem, and half of your problem has been solved.

environment:

• jdk1.8

• maven:3.6.3

• spring boot:2.2.13-RELEASE

• fastjson:1.28.0

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.2.80</version>
</dependency>

Solution

The solution is also very simple, just add a configuration file to annotate fastjson configuration.

 

 Among them, the most important thing is to configure the functions of fastJson through the setSerializerFeatures method of FastJsonConfig

com.alibaba.fastjson.support.config.FastJsonConfig#setSerializerFeatures

/**
 * 返回值过滤器
 * 
 * @Author: 攻城狮白玉 https://blog.csdn.net/zhh763984017
 * @Date: 2022/7/09 18:05
 */
@Configuration
public class FastjsonConverterConfig {

    @Bean
    public HttpMessageConverters customConverters() {
        // 定义一个转换消息的对象

        FastJsonHttpMessageConverter fastConverter = new FastJsonHttpMessageConverter();

        // 添加fastjson的配置信息 比如 ：是否要格式化返回的json数据
        FastJsonConfig fastJsonConfig = new FastJsonConfig();
        // 这里就是核心代码了，WriteMapNullValue把空的值的key也返回
        fastJsonConfig.setSerializerFeatures(SerializerFeature.WriteMapNullValue);

        List<MediaType> fastMediaTypes = new ArrayList<MediaType>();

        // 处理中文乱码问题
        fastJsonConfig.setCharset(Charset.forName("UTF-8"));
        fastMediaTypes.add(MediaType.APPLICATION_JSON_UTF8);
        fastConverter.setSupportedMediaTypes(fastMediaTypes);
        // 在转换器中添加配置信息
        fastConverter.setFastJsonConfig(fastJsonConfig);

        StringHttpMessageConverter stringConverter = new StringHttpMessageConverter();
        stringConverter.setDefaultCharset(Charset.forName("UTF-8"));
        stringConverter.setSupportedMediaTypes(fastMediaTypes);

        // 将转换器添加到converters中
        return new HttpMessageConverters(stringConverter,fastConverter);
    }
}

postscript

It is really not easy to build a new framework from scratch.

Although the original framework has more dependencies and is a bit heavier, there are also many old configurations, which is very fragrant.

However, rebuilding the new framework also made me re-examine a lot of knowledge. For the construction and use of the framework, when it is time to use Occam's razor, I have to use Occam's razor to keep the framework as clean as possible.