解决在使用spring的BeanUtils.copyProperties时，值为null的属性也复制的问题

import org.springframework.beans.BeanUtils;
import org.springframework.beans.BeanWrapper;
import org.springframework.beans.BeanWrapperImpl;

import java.util.HashSet;
import java.util.Set;
 
public class Test {
    public static void main(String[] args) {
        User user = new User();
        user.setName("张三");
        user.setAge(10);
        System.out.println(user);
        System.out.println("复制属性并且复制null============================");
        User copyUser = new User();
        copyUser.setName("李四");
        copyUser.setAge(20);
        copyUser.setSex("男");
        System.out.println(copyUser);
        BeanUtils.copyProperties(user, copyUser);
        System.out.println(copyUser);
        System.out.println("复制属性不复制null============================");
        User copyUser2 = new User();
        copyUser2.setName("赵武");
        copyUser2.setAge(30);
        copyUser2.setSex("女");
        System.out.println(copyUser2);
        BeanUtils.copyProperties(user, copyUser2,getNullPropertyNames(user));
        System.out.println(copyUser2);
    }
    /**
     * 找到source中属性值为null的属性名
     * @param source
     * @return
     */
    public static String[] getNullPropertyNames(Object source) {
        final BeanWrapper src = new BeanWrapperImpl(source);
        java.beans.PropertyDescriptor[] pds = src.getPropertyDescriptors();
        Set emptyNames = new HashSet();
        for(java.beans.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) {//特定字符写在此处过滤，收集不需要copy的字段列表。此处过滤null为例
                emptyNames.add(pd.getName());
            }
        }
        String[] result = new String[emptyNames.size()];
        return (String[]) emptyNames.toArray(result);
    }
}
class User {
    private String name;
    private String sex;
    private Integer age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", sex='" + sex + '\'' +
                ", age=" + age +
                '}';
    }
}