Spring之Ordered Spring之Ordered

在SpringMVC之HandlerMapping中，AbstractHandlerMapping实现了Ordered接口，那么Ordered接口的作用是什么呢？接下来，我们看一下Ordered接口。
Ordered接口
接口定义

public interface Ordered { int HIGHEST_PRECEDENCE = Integer.MIN_VALUE; int LOWEST_PRECEDENCE = Integer.MAX_VALUE; int getOrder(); }//OrderComparator类compare() 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; }int i1 = getOrder(o1); int i2 = getOrder(o2); return (i1 < i2) ? -1 : (i1 > i2) ? 1 : 0; }

上面代码的逻辑: 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。
SpringMVC中Ordered接口例子
修改dispatcher-servlet.xml文件

【Spring之Ordered】

当添加了这段代码，那么SpringMVC默认会注入RequestMappingHandlerAdapter和RequestMappingHandlerMapping这两个类。这时项目就会有两个RequestMappingHandlerMapping，那么这个两个RequestMappingHandlerMapping那个优先级高呢？

initHandlerMappings()源码

//DispatcherServlet类中initHandlerMappings()实现 private void initHandlerMappings(ApplicationContext context) { this.handlerMappings = null; if (this.detectAllHandlerMappings) { // Find all HandlerMappings in the ApplicationContext, including ancestor contexts. Map matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false); if (!matchingBeans.isEmpty()) { this.handlerMappings = new ArrayList(matchingBeans.values()); // We keep HandlerMappings in sorted order. OrderComparator.sort(this.handlerMappings); } } else { try { HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class); this.handlerMappings = Collections.singletonList(hm); } catch (NoSuchBeanDefinitionException ex) { // Ignore, we'll add a default HandlerMapping later. } }// Ensure we have at least one HandlerMapping, by registering // a default HandlerMapping if no other mappings are found. if (this.handlerMappings == null) { this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class); if (logger.isDebugEnabled()) { logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default"); } } }//OrderComparator类中实现排序的方法 public static void sort(List list) { if (list.size() > 1) { Collections.sort(list, INSTANCE); } }@Override public int compare(Object o1, Object o2) { return doCompare(o1, o2, null); }private int doCompare(Object o1, Object o2, OrderSourceProvider sourceProvider) { 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, sourceProvider); int i2 = getOrder(o2, sourceProvider); return (i1 < i2) ? -1 : (i1 > i2) ? 1 : 0; }

通过上面的代码走读得出：如果配置了，又配置了自定义的RequestMappingHandlerMapping，并且没有设置自定义RequestMappingHandlerMapping的order值。那么配置的RequestMappingHandlerMapping优先级高，因为内部会设置RequestMappingHandlerMapping的order为0。我们可以将自定义的RequestMappingHandlerMapping的order设置为-1提高它的优先级。

备注：
自定义的RequestMappingHandlerAdapter和的优先级？自定义AdapterRequestMappingHandlerAdapter没有设置order的值情况下，* 谁先定义谁的优先级高*。具体我们可以走读initHandlerAdapters(context)。
作者：忘净空
链接：https://www.jianshu.com/p/d87e5de747a5
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