Spring BeanUtils如何忽略空值拷贝

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BeanUtils类所在的包

有两个包都提供了BeanUtils类：

Spring的（推荐）：org.springframework.beans.BeanUtilsApache的：org.apache.commons.beanutils.BeanUtils

忽略null值拷贝属性的用法

BeanUtils.copyProperties(Object source, Object target, String... ignoreProperties)

获取null属性名（工具类）

可以自己写一个工具类，用来获取对象里所有null的属性名字。

package com.example.util; import org.springframework.beans.BeanWrapper;import org.springframework.beans.BeanWrapperImpl;import java.beans.PropertyDescriptor;import java.util.HashSet;import java.util.Set;public class PropertyUtil {    public static String[] getNullPropertyNames(Object source) {        BeanWrapper src = new BeanWrapperImpl(source);        PropertyDescriptor[] pds = src.getPropertyDescriptors();        Set emptyNames = new HashSet<>();        for (PropertyDescriptor pd : pds) {            //check if value of this property is null then add it to the collection            Object srcValue = src.getPropertyValue(pd.getName());            if (srcValue == null){                emptyNames.add(pd.getName());            }        }        String[] result = new String[emptyNames.size()];        return emptyNames.toArray(result);    }}

示例

本处为了全面，将以下几种情况都考虑进去：

• 继承了某个类

• 某个属性是个Entity

工具类

package com.example.util; import org.springframework.beans.BeanWrapper;import org.springframework.beans.BeanWrapperImpl;import java.beans.PropertyDescriptor;import java.util.HashSet;import java.util.Set;public class PropertyUtil {    public static String[] getNullPropertyNames(Object source) {        BeanWrapper src = new BeanWrapperImpl(source);        PropertyDescriptor[] pds = src.getPropertyDescriptors();        Set emptyNames = new HashSet<>();        for (PropertyDescriptor pd : pds) {            //check if value of this property is null then add it to the collection            Object srcValue = src.getPropertyValue(pd.getName());            if (srcValue == null){                emptyNames.add(pd.getName());            }        }        String[] result = new String[emptyNames.size()];        return emptyNames.toArray(result);    }}

Entity

基础Entity

package com.example.entity; import com.fasterxml.jackson.annotation.JsonFormat;import lombok.Data;import java.time.LocalDateTime;@Datapublic class BaseEntity {    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss",timezone="GMT+8")    private LocalDateTime createTime;    private LocalDateTime updateTime;    private Long deletedFlag;}

User

package com.example.entity; import lombok.Data;@Datapublic class User {    private Long id;    private String userName;    private String nickName;    // 0:正常 1：被锁定    private Integer status;}

Blog

package com.example.entity; import lombok.Data;import lombok.EqualsAndHashCode;@Data@EqualsAndHashCode(callSuper = true)public class Blog extends BaseEntity{    private Long id;    private String title;    private String content;    private User user;}

VO

package com.example.vo; import com.example.entity.BaseEntity;import com.example.entity.User;import lombok.Data;import lombok.EqualsAndHashCode;@Data@EqualsAndHashCode(callSuper = true)public class BlogRequest extends BaseEntity {    private Long id;    private String title;    private String content;    private User user;}

Controller

package com.example.controller; import com.example.entity.Blog;import com.example.entity.User;import com.example.util.PropertyUtil;import com.example.vo.BlogRequest;import com.fasterxml.jackson.core.JsonProcessingException;import com.fasterxml.jackson.databind.ObjectMapper;import org.springframework.beans.BeanUtils;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.web.bind.annotation.GetMapping;import org.springframework.web.bind.annotation.RestController;import java.time.LocalDateTime;import java.util.Arrays;@RestControllerpublic class HelloController {    @Autowired    private ObjectMapper objectMapper;    @GetMapping("/test")    public String test() {        BlogRequest blogRequest = new BlogRequest();        blogRequest.setId(10L);        blogRequest.setTitle("Java实战");        // blogRequest.setContent("本文介绍获取null的字段名的方法");        blogRequest.setUser(new User());        blogRequest.setCreateTime(LocalDateTime.now());        // blogRequest.setCreateTime(LocalDateTime.now());        blogRequest.setDeletedFlag(0L);        User user = new User();        user.setId(15L);        user.setUserName("Tony");        // user.setNickName("Iron Man");        // user.setStatus(1);        String[] nullPropertyNames = PropertyUtil.getNullPropertyNames(blogRequest);        System.out.println(Arrays.toString(nullPropertyNames));        System.out.println("------------------------------");        Blog blog = new Blog();        BeanUtils.copyProperties(blogRequest, blog, nullPropertyNames);        try {            System.out.println(objectMapper.writeValueAsString(blog));        } catch (JsonProcessingException e) {            e.printStackTrace();        }        return "test success";    }}

测试

访问：http://localhost:8080/test/

后端结果：

[updateTime, content]------------------------------{"createTime":"2022-03-17 19:58:32","updateTime":null,"deletedFlag":0,"id":10,"title":"Java实战","content":null,"user":{"id":null,"userName":null,"nickName":null,"status":null}}

结论

• 可以获取父类的null的属性名

• 不可以获取属性的null的属性名

其他文件

pom.xml

    4.0.0            org.springframework.boot        spring-boot-starter-parent        2.3.0.RELEASE                 com.example    demo_SpringBoot    0.0.1-SNAPSHOT    demo_SpringBoot    Demo project for Spring Boot             1.8                             org.springframework.boot            spring-boot-starter-web                             org.projectlombok            lombok            1.16.20            provided                                                      org.springframework.boot                spring-boot-maven-plugin                2.3.0.RELEASE                         

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