Spring Ordered接口

        Java中的对象排序都会跟Comparable Comparator 这两个接口扯上关系，下面我们要说说Spring排序接口Ordered。

public interface Ordered {

	/**
	 * Useful constant for the highest precedence value.
	 * @see java.lang.Integer#MIN_VALUE
	 */
	int HIGHEST_PRECEDENCE = Integer.MIN_VALUE;

	/**
	 * Useful constant for the lowest precedence value.
	 * @see java.lang.Integer#MAX_VALUE
	 */
	int LOWEST_PRECEDENCE = Integer.MAX_VALUE;


	/**
	 * Return the order value of this object, with a
	 * higher value meaning greater in terms of sorting.
	 * <p>Normally starting with 0, with {@code Integer.MAX_VALUE}
	 * indicating the greatest value. Same order values will result
	 * in arbitrary positions for the affected objects.
	 * <p>Higher values can be interpreted as lower priority. As a
	 * consequence, the object with the lowest value has highest priority
	 * (somewhat analogous to Servlet "load-on-startup" values).
	 * @return the order value
	 */
	int getOrder();

}

只有1个方法：getOrder()；  2个变量：最高级(数值最小)和最低级(数值最大)。

public interface PriorityOrdered extends Ordered {

}

PriorityOrdered是个接口，继承自Ordered接口，未定义任何方法。

public class OrderComparator implements Comparator<Object> {

	/**
	 * Shared default instance of OrderComparator.
	 */
	public static final OrderComparator INSTANCE = new OrderComparator();


	public int compare(Object o1, Object o2) {
		boolean p1 = (o1 instanceof PriorityOrdered);
		boolean p2 = (o2 instanceof PriorityOrdered);
		if (p1 && !p2) {
			return -1;
		}
		else if (p2 && !p1) {
			return 1;
		}

		// Direct evaluation instead of Integer.compareTo to avoid unnecessary object creation.
		int i1 = getOrder(o1);
		int i2 = getOrder(o2);
		return (i1 < i2) ? -1 : (i1 > i2) ? 1 : 0;
	}

	/**
	 * Determine the order value for the given object.
	 * <p>The default implementation checks against the {@link Ordered}
	 * interface. Can be overridden in subclasses.
	 * @param obj the object to check
	 * @return the order value, or {@code Ordered.LOWEST_PRECEDENCE} as fallback
	 */
	protected int getOrder(Object obj) {
		return (obj instanceof Ordered ? ((Ordered) obj).getOrder() : Ordered.LOWEST_PRECEDENCE);
	}


	/**
	 * Sort the given List with a default OrderComparator.
	 * <p>Optimized to skip sorting for lists with size 0 or 1,
	 * in order to avoid unnecessary array extraction.
	 * @param list the List to sort
	 * @see java.util.Collections#sort(java.util.List, java.util.Comparator)
	 */
	public static void sort(List<?> list) {
		if (list.size() > 1) {
			Collections.sort(list, INSTANCE);
		}
	}

	/**
	 * Sort the given array with a default OrderComparator.
	 * <p>Optimized to skip sorting for lists with size 0 or 1,
	 * in order to avoid unnecessary array extraction.
	 * @param array the array to sort
	 * @see java.util.Arrays#sort(Object[], java.util.Comparator)
	 */
	public static void sort(Object[] array) {
		if (array.length > 1) {
			Arrays.sort(array, INSTANCE);
		}
	}

}

OrderComparator类：实现了Comparator的一个比较器。
它提供了2个静态排序方法：sort(List<?> list)、sort(Object[] array)。对数组和集合进行排序。

总结：

       OrderComparator比较器进行排序的时候，若2个对象中有一个对象实现了PriorityOrdered接口，那么这个对象的优先级更高。
　　若2个对象都是PriorityOrdered或Ordered接口的实现类，那么比较Ordered接口的getOrder方法得到order值，值越低，优先级越高。