Security 中的Filters的顺序

Spring Security 已经定义了一些 Filter，不管实际应用中你用到了哪些，它们应当保持如下顺序,来自SecurityFilters的枚举

在添加自定义的过滤器的时候，通过设置after/before/position来设置其过滤器对应的order值决定此过滤器在过滤器链中的位置如何

那么如何根据这些属性值进行排序呢？我们来看一下代码

    List<OrderDecorator> buildCustomFilterList(Element element, ParserContext pc) {
        List<Element> customFilterElts = DomUtils.getChildElementsByTagName(element, Elements.CUSTOM_FILTER);
        List<OrderDecorator> customFilters = new ArrayList<OrderDecorator>();

        final String ATT_AFTER = "after";
        final String ATT_BEFORE = "before";
        final String ATT_POSITION = "position";

        for (Element elt: customFilterElts) {
            String after = elt.getAttribute(ATT_AFTER);
            String before = elt.getAttribute(ATT_BEFORE);
            String position = elt.getAttribute(ATT_POSITION);

            String ref = elt.getAttribute(ATT_REF);

            if (!StringUtils.hasText(ref)) {
                pc.getReaderContext().error("The '" + ATT_REF + "' attribute must be supplied", pc.extractSource(elt));
            }

            RuntimeBeanReference bean = new RuntimeBeanReference(ref);

            if(WebConfigUtils.countNonEmpty(new String[] {after, before, position}) != 1) {
                pc.getReaderContext().error("A single '" + ATT_AFTER + "', '" + ATT_BEFORE + "', or '" +
                        ATT_POSITION + "' attribute must be supplied", pc.extractSource(elt));
            }

            if (StringUtils.hasText(position)) {
                //如果设置了position属性值，则替换掉默认的过滤器
               customFilters.add(new OrderDecorator(bean, SecurityFilters.valueOf(position)));
            } else if (StringUtils.hasText(after)) {
                SecurityFilters order = SecurityFilters.valueOf(after);
                if (order == SecurityFilters.LAST) {
                    customFilters.add(new OrderDecorator(bean, SecurityFilters.LAST));
                } else {
                    //如果设置成after，则order值在此基础上加1
                   customFilters.add(new OrderDecorator(bean, order.getOrder() + 1));
                }
            } else if (StringUtils.hasText(before)) {
                SecurityFilters order = SecurityFilters.valueOf(before);
                if (order == SecurityFilters.FIRST) {
                    customFilters.add(new OrderDecorator(bean, SecurityFilters.FIRST));
                } else {
                    //如果设置成after，则order值在此基础上减1

  customFilters.add(new OrderDecorator(bean, order.getOrder() - 1)); } } } return customFilters; }

最终在调用Collections.sort(unorderedFilterChain, new OrderComparator());时，根据order值进行排序

下面是OrderComparator的compare方法的实现

	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;
	}