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Spring工具类–BeanUtils忽略空值拷贝

简介

说明

本文用示例介绍Spring(SpringBoot)如何使用BeanUtils拷贝对象属性(忽略空值)。

BeanUtils类所在的包

有两个包都提供了BeanUtils类:

  1. Spring的(推荐):org.springframework.beans.BeanUtils
  2. Apache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)

示例

本处为了全面,将以下几种情况都考虑进去:

  1. 继承了某个类
  2. 某个属性是个Entity

可以自己写一个工具类,用来获取对象里所有null或者空字符串的属性名字。

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[] readEmptyPropertyNames(Object source) {
        BeanWrapper src = new BeanWrapperImpl(source);
        PropertyDescriptor[] pds = src.getPropertyDescriptors();
        Set<String> emptyNames = new HashSet<>();
        for (PropertyDescriptor pd : pds) {
            String filedName = pd.getName();
            Object srcValue = src.getPropertyValue(pd.getName());
            if (srcValue == null) {
                emptyNames.add(filedName);
            } else {
                if (srcValue instanceof String) {
                    if (!StringUtils.hasText((String) srcValue)) {
                        emptyNames.add(filedName);
                    }
                }
            }
        }
        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;

@Data
public class BaseEntity {
    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss",timezone="GMT+8")
    private LocalDateTime createTime;

    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss",timezone="GMT+8")
    private LocalDateTime updateTime;

    private Long deletedFlag;
}

User

package com.example.entity;

import lombok.Data;

@Data
public 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;

@RestController
public 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

  1. 可以获取父类的null的属性名
  2. 不可以获取属性的null的属性名

 pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.3.0.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>demo_SpringBoot</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo_SpringBoot</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.16.20</version>
            <scope>provided</scope>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>2.3.0.RELEASE</version>
            </plugin>
        </plugins>
    </build>

</project>
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