Struts2中EL表达式的取值顺序及OGNL表达式的取值顺序

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好记性不如赖笔头…………

正常EL的查找域为：page(PageContext)–>request–>session–>application

Struts2中EL的查找域为：page(PageContext)–>request–>contextMap–>ValueStack–>session–>application

有的人说Struts2中EL的取值顺序是：page(PageContext)–>request–>ValueStack–>contextMap–>session–>application，
但查看源码（org.apache.struts2.dispatcher.StrutsRequestWrapper）发现request中的取值顺序如下：

 public Object getAttribute(String key) {        if (key == null) {            throw new NullPointerException("You must specify a key value");        }        if (disableRequestAttributeValueStackLookup || key.startsWith("javax.servlet")) {            // don't bother with the standard javax.servlet attributes, we can short-circuit this            // see WW-953 and the forums post linked in that issue for more info            return super.getAttribute(key);        }        **//注意，这里是先查找的actionContext中的contextMap的内容**        ActionContext ctx = ActionContext.getContext();        Object attribute = super.getAttribute(key);        if (ctx != null && attribute == null) {            boolean alreadyIn = isTrue((Boolean) ctx.get(REQUEST_WRAPPER_GET_ATTRIBUTE));            // note: we don't let # come through or else a request for            // #attr.foo or #request.foo could cause an endless loop            if (!alreadyIn && !key.contains("#")) {                try {                    // If not found, then try the ValueStack                    ctx.put(REQUEST_WRAPPER_GET_ATTRIBUTE, Boolean.TRUE);                    **//最后，如果request、contextMap都没有，才去的valueStacK去查找**                    ValueStack stack = ctx.getValueStack();                    if (stack != null) {                        attribute = stack.findValue(key);                    }                } finally {                    ctx.put(REQUEST_WRAPPER_GET_ATTRIBUTE, Boolean.FALSE);                }            }        }        return attribute;    }

OGNL的查找域为：page(PageContext)–>ValueStack–>contextMap–>request–>session–>application

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