为何使用

在项目实际开发中，经常需要将两个对象实例进行属性复制，从而对源数据进行后续操作，而不改变源对象属性信息。

这种转换最原始的方法就是手写大量的 get/set 代码，这是在开发过程中不愿去做的，因为它显得很繁琐。为了解决这个问题，就诞生了一些方便的库，常用的有 apache 的 BeanUtils 和 Spring 的 BeanUtils。

浅拷贝与深拷贝

• 浅拷贝
  对基本数据类型进行值传递，对引用数据类型进行引用传递般的拷贝，此为浅拷贝
• 深拷贝
  对基本数据类型进行值传递，对引用数据类型，创建一个新的对象，并复制其内容，此为深拷贝。

Spring 的 BeanUtils

 /**
* Copy the property values of the given source bean into the given target bean.
* 把给定源 bean 的属性复制到给定目标 bean 中。
* <p>Note: The source and target classes do not have to match or even be derived
* from each other, as long as the properties match. Any bean properties that the
* source bean exposes but the target bean does not will silently be ignored.
* 注意：源类与目标类不必匹配甚至不必派生。源 bean 公开但是目标 bean 没有公开的属性都会被忽略
* @param source the source bean
* @param target the target bean
* @param editable the class (or interface) to restrict property setting to
* @param ignoreProperties array of property names to ignore
* @throws BeansException if the copying failed
* source：源 bean，target：目标 bean，ignoreProperties：要忽略的属性名数组
* @see BeanWrapper
*/
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());
			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);
						if (!Modifier.isPublic(writeMethod.getDeclaringClass().getModifiers())) {
							writeMethod.setAccessible(true);
						}
						writeMethod.invoke(target, value);
					}
					catch (Throwable ex) {
						throw new FatalBeanException(
								"Could not copy property '" + targetPd.getName() + "' from source to target", ex);
					}
				}
			}
		}
	}
}

自定义 BeanUtils

public abstract class BeanUtil {
    public static Object copyProperties(Object source, Object target, String... ignoreProperties) {
        if (source == null) {
            return target;
        }
        BeanUtils.copyProperties(source, target, ignoreProperties);
        return target;
    }

    public static <T> List<T> copyList(List<?> sources, Class<T> clazz) {
        return copyList(sources, clazz, null);
    }
    // 复制 List<T> 类型的 bean
    public static <T> List<T> copyList(List<?> sources, Class<T> clazz, Callback<T> callback) {
        List<T> targetList = new ArrayList<>();
        if (sources != null) {
            try {
                for (Object source : sources) {
                    T target = clazz.newInstance();
                    copyProperties(source, target);
                    if (callback != null) {
                        callback.set(source, target);
                    }
                    targetList.add(target);
                }
            } catch (InstantiationException e) {
                e.printStackTrace();
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }
        }
        return targetList;
    }

    public static interface Callback<T> {
        void set(Object source, T target);
    }
}