package com.abc.demo;

import java.util.Arrays;
import java.util.List;
import org.springframework.beans.BeanUtils;

public class Main {

  public static void main(String[] args) {
    List<Article> articleList = Arrays.asList(new Article(1L, "hello world"));

    Member m1 = new Member("Eddy", articleList);
    Member m2 = new Member();
    BeanUtils.copyProperties(m1, m2);

    System.out.println("m1:" + m1); // m1:name:Eddy, articleList:[id:1, content:hello world]
    System.out.println("m2:" + m2); // m2:name:Eddy, articleList:[id:1, content:hello world]
  }
}

class Member {
  private String name;
  private List<Article> articleList;

  public Member() {}

  public Member(String name, List<Article> articleList) {
    this.name = name;
    this.articleList = articleList;
  }

  @Override
  public String toString() {
    return "name:" + name + ", " + "articleList:" + articleList;
  }
// getters and setters
}

class Article {
  private Long id;
  private String content;

  public Article(Long id, String content) {
    this.id = id;
    this.content = content;
  }

  @Override
  public String toString() {
    return "id:" + id + ", content:" + content;
  }
// getters and setters
}

package com.abc.demo;

import java.util.Arrays;
import java.util.List;
import org.springframework.beans.BeanUtils;

public class Main {

  public static void main(String[] args) {
    List<Article> articleList = Arrays.asList(new Article(1L, "hello world"));

    Member m1 = new Member("Eddy", articleList);

    User u1 = new User();
    BeanUtils.copyProperties(m1, u1);

    System.out.println("m1:" + m1); // m1:name:Eddy, articleList:[id:1, content:hello world]
    System.out.println("u1:" + u1); // u1:name:Eddy, articlelist:null
  }
}

class Member {
  private String name;
  private List<Article> articleList; // <-- small camel case

  public Member() {}

  public Member(String name, List<Article> articleList) {
    this.name = name;
    this.articleList = articleList;
  }

  @Override
  public String toString() {
    return "name:" + name + ", " + "articleList:" + articleList;
  }
// getters and setters
}

class Article {
  private Long id;
  private String content;

  public Article(Long id, String content) {
    this.id = id;
    this.content = content;
  }

  @Override
  public String toString() {
    return "id:" + id + ", content:" + content;
  }
// getters and setters
}

class User {
  private String name;
  private String articlelist; // <-- all lowercase

  public String getName() {
    return name;
  }

  @Override
  public String toString() {
    return "name:" + name + ", " + "articleList:" + articlelist;
  }
// getters and setters
}

public abstract class BeanUtils {
    ...
    private static void copyProperties(Object source, Object target, @Nullable Class<?> editable,
            @Nullable String... ignoreProperties) throws BeansException {

        Assert.notNull(source, "Source must not be null");
        Assert.notNull(target, "Target must not be null");

        Class<?> actualEditable = target.getClass();
        if (editable != null) {
            if (!editable.isInstance(target)) {
                throw new IllegalArgumentException("Target class [" + target.getClass().getName() +
                        "] not assignable to Editable class [" + editable.getName() + "]");
            }
            actualEditable = editable;
        }
        PropertyDescriptor[] targetPds = getPropertyDescriptors(actualEditable);
        List<String> ignoreList = (ignoreProperties != null ? Arrays.asList(ignoreProperties) : null);

        for (PropertyDescriptor targetPd : targetPds) {
            Method writeMethod = targetPd.getWriteMethod();
            if (writeMethod != null && (ignoreList == null || !ignoreList.contains(targetPd.getName()))) {
                PropertyDescriptor sourcePd = getPropertyDescriptor(source.getClass(), targetPd.getName()); // 以目的對象(target)的屬性名稱來取得來源對象(source)的屬性
                if (sourcePd != null) {
                    Method readMethod = sourcePd.getReadMethod();
                    if (readMethod != null &&
                            ClassUtils.isAssignable(writeMethod.getParameterTypes()[0], readMethod.getReturnType())) {
                        try {
                            if (!Modifier.isPublic(readMethod.getDeclaringClass().getModifiers())) {
                                readMethod.setAccessible(true);
                            }
                            Object value = readMethod.invoke(source); // 取得來源對象的屬性值
                            if (!Modifier.isPublic(writeMethod.getDeclaringClass().getModifiers())) {
                                writeMethod.setAccessible(true);
                            }
                            writeMethod.invoke(target, value); // 把來源對象的屬性值寫入目的對象的同名屬性
                        }
                        catch (Throwable ex) {
                            throw new FatalBeanException(
                                    "Could not copy property '" + targetPd.getName() + "' from source to target", ex);
                        }
                    }
                }
            }
        }
    }
    ...
}