java 复制非空对象属性值

很多时候，我们需要通过对象拷贝，比如说VO类与数据库实体bean类、更新时非空对象不更新，对同一对象不同数据分开存储等

用于对象拷贝，spring 和 Apache都提供了相应的工具类方法，BeanUtils.copyProperties

但是对于非空属性拷贝就需要自己处理了

在这里借用spring中org.springframework.beans.BeanUtils类提供的方法copyProperties(Object source, Object target, String... ignoreProperties) 

/**
	 * Copy the property values of the given source bean into the given target bean,
	 * ignoring the given "ignoreProperties".
	 * <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.
	 * <p>This is just a convenience method. For more complex transfer needs,
	 * consider using a full BeanWrapper.
	 * @param source the source bean
	 * @param target the target bean
	 * @param ignoreProperties array of property names to ignore
	 * @throws BeansException if the copying failed
	 * @see BeanWrapper
	 */
	public static void copyProperties(Object source, Object target, String... ignoreProperties) throws BeansException {
		copyProperties(source, target, null, ignoreProperties);
/**

* Copy the property values of the given source bean into the given target bean.

* <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.

* @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

* @see BeanWrapper

*/

private static void copyProperties(Object source, Object target, Class<?> editable, String... ignoreProperties)

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

	Class&lt;?&gt; 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&lt;String&gt; ignoreList = (ignoreProperties != null ? Arrays.asList(ignoreProperties) : null);

	for (PropertyDescriptor targetPd : targetPds) {
		Method writeMethod = targetPd.getWriteMethod();
		if (writeMethod != null &amp;&amp; (ignoreList == null || !ignoreList.contains(targetPd.getName()))) {
			PropertyDescriptor sourcePd = getPropertyDescriptor(source.getClass(), targetPd.getName());
			if (sourcePd != null) {
				Method readMethod = sourcePd.getReadMethod();
				if (readMethod != null &amp;&amp;
						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);
					}
				}
			}
		}
	}
}

然后封装一下得到以下方法：

/**
	 * @author 郑明亮
	 * @Email zhengmingliang911@gmail.com
	 * @Time 2017年2月14日 下午5:14:25
	 * @Description <p>获取到对象中属性为null的属性名  </P>
	 * @param source 要拷贝的对象
	 * @return
	 */
	public static String[] getNullPropertyNames(Object source) {
		final BeanWrapper src = new BeanWrapperImpl(source);
		java.beans.PropertyDescriptor[] pds = src.getPropertyDescriptors();
	Set&lt;String&gt; emptyNames = new HashSet&lt;String&gt;();
	for (java.beans.PropertyDescriptor pd : pds) {
		Object srcValue = src.getPropertyValue(pd.getName());
		if (srcValue == null)
			emptyNames.add(pd.getName());
	}
	String[] result = new String[emptyNames.size()];
	return emptyNames.toArray(result);
}

/**
 * @author 郑明亮
 * @Email zhengmingliang911@gmail.com
 * @Time 2017年2月14日 下午5:15:30
 * @Description &lt;p&gt; 拷贝非空对象属性值 &lt;/P&gt;
 * @param source 源对象
 * @param target 目标对象
 */
public static void copyPropertiesIgnoreNull(Object source, Object target) {
	BeanUtils.copyProperties(source, target, getNullPropertyNames(source));
}</pre>

 
测试方法就不提供了，自行测试即可
 如果项目中使用的框架有Hibernate的话，则可以通过在实体类上添加下面两条注解
@DynamicInsert(true)
@DynamicUpdate(true)
如果想对该注解进一步了解的话，那么可以去官网看英文文档，文档解释的很清楚，在此不再赘述了
https://www.mkyong.com/hibernate/hibernate-dynamic-insert-attribute-example/