笔者是在 config 配置文件夹内创建 ApplicationReadyListener.class 文件，该文件内容如下复制粘贴： @Configuration 注解能很方便的将本文件解释为配置文件

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationListener;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.event.ContextRefreshedEvent;
import org.springframework.data.mongodb.core.MongoTemplate;
import org.springframework.data.mongodb.core.convert.DefaultMongoTypeMapper;
import org.springframework.data.mongodb.core.convert.MappingMongoConverter;
import org.springframework.data.mongodb.core.convert.MongoConverter;
 
 
@Configuration
public class ApplicationReadyListener implements ApplicationListener<ContextRefreshedEvent> {
 
    @Autowired
    MongoTemplate mongoTemplate;
 
    @Override
    public void onApplicationEvent(ContextRefreshedEvent contextRefreshedEvent) {
        MongoConverter converter = mongoTemplate.getConverter();
        if (converter.getTypeMapper().isTypeKey("_class")) {
            ((MappingMongoConverter) converter).setTypeMapper(new DefaultMongoTypeMapper(null));
        }
    }
}

参考链接

1. Spring 框架 MongoDB 去掉_class属性字段