Spring BeanUtils忽略空值拷貝的方法範例程式碼

2022-03-18 13:01:12

簡介

說明

本文用範例介紹Spring（SpringBoot）如何使用BeanUtils拷貝物件屬性（忽略空值）。

BeanUtils類所在的包

有兩個包都提供了BeanUtils類：

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

忽略null值拷貝屬性的用法

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

獲取null屬性名（工具類）

可以自己寫一個工具類，用來獲取物件裡所有null的屬性名字。

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<String> 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);
    }
}

範例

本處為了全面，將以下幾種情況都考慮進去：

繼承了某個類
某個屬性是個Entity

工具類

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<String> 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

基礎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;
    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：被鎖定
    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;
}

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實戰");
        // blogRequest.setContent("本文介紹獲取null的欄位名的方法");
        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";
    }
}

測試

存取：http://localhost:8080/test/

後端結果：

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

結論

可以獲取父類別的null的屬性名
不可以獲取屬性的null的屬性名

其他檔案

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>