SpringBoot 更新业务场景下，如何区分null是清空属性值 还是null为vo属性默认值?

先看歧义现象

值为null

未传递此属性


所以此时如何区分null 时传递进来的的null，还是属性的默认值null?

引入方案

引入过滤器，中间截获requestBodyData并保存到HttpServletRequest，业务层从HttpServletRequest 获取到requestBodyData辅助判断此属性为未传递还是值为null

第1步：定义并注册过滤器

自定义过滤器截获requestBodyData并保存到HttpServletRequest

import com.practisesvr.utils.http.FilterHttpServletRequest;
import jakarta.servlet.FilterChain;
import jakarta.servlet.ServletException;
import jakarta.servlet.ServletRequest;
import jakarta.servlet.ServletResponse;
import jakarta.servlet.http.HttpServletRequest;
import org.springframework.stereotype.Component;
import org.springframework.web.filter.GenericFilterBean;import java.io.IOException;@Component
public class RequestCheckFilter extends GenericFilterBean {@Overridepublic void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {System.err.println("***RequestHeaderCheckFilter.doFilter.start***");if (!(request instanceof HttpServletRequest)) {throw new IllegalStateException("Expected HttpServletRequest");}HttpServletRequest httpRequest = (HttpServletRequest) request;FilterHttpServletRequest filterHttpRequest = new FilterHttpServletRequest(httpRequest);String body = filterHttpRequest.getBody();filterHttpRequest.setAttribute("requestBodyData", body);// 继续执行filter链chain.doFilter(filterHttpRequest, response);System.err.println("***RequestHeaderCheckFilter.doFilter.end***");}
}

[Ref： 过滤器使用到 HttpServletRequestWrapper 参考如下 ] What is HttpServletRequestWrapper does?

注册过滤器

@Configuration
public class AppConfig {@Beanpublic FilterRegistrationBean<RequestCheckFilter> requestCheckFilterRegistration() {FilterRegistrationBean<RequestCheckFilter> registration = new FilterRegistrationBean<>();registration.setFilter(new RequestCheckFilter());// 可以设置过滤器名称registration.setName("requestCheckFilter");// 设置拦截规则registration.addUrlPatterns("/*"); // 拦截所有请求// 设置过滤器执行顺序，默认为0，数值越小优先级越高registration.setOrder(2);return registration;}
}

第2步：从HttpServletRequest 获取到requestBodyData

public class RequestIUtils {/*** 从当前请求上下文中获取并解析请求体数据，将其转换为Map类型对象.** @return 如果成功获取到请求体数据并转换成功，则返回一个包含请求体内容的Map对象；* 若RequestAttributes不存在或请求体数据为空，则返回一个新的空HashMap对象。*/public static Map<String, Object> getRequestBodyBody() {RequestAttributes requestAttributes = RequestContextHolder.getRequestAttributes();if (requestAttributes == null) {return new HashMap<>();}HttpServletRequest request = ((ServletRequestAttributes) requestAttributes).getRequest();Object requestBody = request.getAttribute("requestBodyData");if (requestBody == null) {return new HashMap<>();}return JsonUtils.jsonToT(requestBody.toString(), Map.class);}
}    

第3步：业务层使用requestBodyData辅助判断

@Override
public Student update(Student student) {Map<String, Object> requestBody = RequestIUtils.getRequestBodyBody();Student stu = new Student();stu.setId(student.getId());stu.setUsername(student.getUsername());stu.setPassword(student.getPassword());stu.setAge(student.getAge());stu.setHeight(student.getHeight());stu.setGender(student.getGender());// 使用方式if (requestBody.containsKey("classId")){stu.setClassId(student.getClassId());}stu.setIsDelete(student.getIsDelete());this.studentsMapper.update(student);return this.queryById(student.getId());
}