set標籤注意的地方

set標籤是將某個值放到指定範圍內， 好比說 student.teacher.parent.age 每次訪問這個屬性不只性能低，並且代碼可讀性不好，爲了解決這個問題，能夠將這個值設置爲一個新值，而且放入指定範圍內 
name 是必填屬性，是從新生成的新變量的名字 
scope 可選屬性，指定新變量被放置的範圍，能夠接受application,session,request,page,action 這5個值 沒有指定默認是Stack Context中 
value 可選屬性，指定變量的值 若是沒有指定，使用ValueStack棧頂的值賦給新變量 
id 可選屬性，指定新元素的引用ID 

下面是個例子： 

<!-- 使用bean標籤訂義一個javaBean實例--!> 
<s:bean name="lee.Person" id="p"> 
<s:param name="name" value="zhangsan"/> 
<s:param name="age" value="29"/> 
</s:bean> 
將p放入默認範圍內 
<s:set value="#p" name="test"/> 
<s:property value="#test.name"/> <br> 
<s:property value="#test.age"/> <br> 
將p放入application範圍內。 
<s:set value="#p" name="test" scope="application"/> 
<s:property value="#attr.test.name"/> <br> 
<s:property value="#attr.test.age"/> <br> 
將p放入session範圍內。 
<s:set value="#p" name="test" scope="session"/> 
${sessionScope.test.name} <br> 
${sessionScope.test.age} <br>

這裏發現一個struts2 s標籤問題，<s:set value="jkadf1213" name="test"/> $｛test｝發現了獲取不到值，value="'jkadf1213'" 若是是字符串的話，在雙引號裏面還要加單引號才能獲取到值。

 

關於struts2裏面s:set 和s:if的問題，

<s:set name="seasonList" value="{'Spring',Summer,'Autumn','Winter'}" />

<span style="font-size: small;"><s:set name="seasonList" value="{'Spring',Summer,'Autumn','Winter'}" /></span>

<s:set name="seasonList" value="{'Spring',Summer,'Autumn','Winter'}" />

這麼是正確的，可是咱們set一個map，這樣就不行了： 

<s:set name="monthMap" value='#{"1":"Jan","2":"Feb","3":"Mar","4":"Apr","5":"May",
"6":"Jun","7":"Jul","8":"Aug","9":"Sep","10":"Oct","11":"Nov","12":"Dec"}' />

<span style="font-size: small;"><s:set name="monthMap" value='#{"1":"Jan","2":"Feb","3":"Mar","4":"Apr","5":"May",
"6":"Jun","7":"Jul","8":"Aug","9":"Sep","10":"Oct","11":"Nov","12":"Dec"}' />
</span>

<s:set name="monthMap" value='#{"1":"Jan","2":"Feb","3":"Mar","4":"Apr","5":"May","6":"Jun","7":"Jul","8":"Aug","9":"Sep","10":"Oct","11":"Nov","12":"Dec"}' />

奇怪的是，前面必需要加一個#，感受很奇怪，我也不知道爲何，但願研究過源碼的給一個解答。 

<span class="s">
                        <s:set name="monthMap" value="#{'1':'Jan','2':'Feb','3':'Mar','4':'Apr','5':'May','6':'Jun','7':'Jul','8':'Aug','9':'Sep','10':'Oct','11':'Nov','12':'Dec'}" />
                        <s:set name="currentMonth" value="%{ chargeMonth }" />
                        <select name="chargeMonth"class="styled">
                            <option value=" ">-- Select Month --</option>
                            <s:iterator value="#monthMap" id="month">
                                <option value="<s:property value='key'/>"
                                        <s:if test="%{key==#currentMonth}">
                                            selected="selected"
                                        </s:if>
                                        >
                                    <s:property value='value'/>
                                </option>
                            </s:iterator>
                        </select>

<span style="font-size: small;"><span class="s">
     <s:set name="monthMap" value="#{'1':'Jan','2':'Feb','3':'Mar','4':'Apr','5':'May','6':'Jun','7':'Jul','8':'Aug','9':'Sep','10':'Oct','11':'Nov','12':'Dec'}" />
     <s:set name="currentMonth" value="%{ chargeMonth }" />
    <select name="chargeMonth"class="styled">
        <option value=" ">-- Select Month --</option>
        <s:iterator value="#monthMap" id="month">
        <option value="<s:property value='key'/>"
        <s:if test="%{key==#currentMonth}">
            selected="selected"
        </s:if>
            >
        <s:property value='value'/>
        </option>
        </s:iterator>
         </select></span>

<span class="s">     <s:set name="monthMap" value="#{'1':'Jan','2':'Feb','3':'Mar','4':'Apr','5':'May','6':'Jun','7':'Jul','8':'Aug','9':'Sep','10':'Oct','11':'Nov','12':'Dec'}" />     <s:set name="currentMonth" value="%{ chargeMonth }" /><select name="chargeMonth"  class="styled">   <option value=" ">-- Select Month --</option><s:iterator value="#monthMap" id="month"><option value="<s:property value='key'/>"<s:if test="%{key==#currentMonth}">selected="selected"</s:if>><s:property value='value'/></option></s:iterator>         </select>

發現這樣不行，後來通過我反覆的測試，當選擇10，11，12時候能正確的將selected加上，可是選擇前面的數字怎麼都不行，後來經我觀察，前面我將字符串用的是’，估計在後臺反射的時候將其類型錯誤的轉化成char類型了，可是估計當判斷length大於1的時候，將其轉化成字符串了，因此可以正確。不知道我這麼猜的對不對，貼出來分享一下吧，之後但願這樣的問題不能在犯了。 
我修改成下面的就能夠了： 

<s:set name="monthMap" value='#{"1":"Jan","2":"Feb","3":"Mar","4":"Apr","5":"May","6":"Jun","7":"Jul","8":"Aug","9":"Sep","10":"Oct","11":"Nov","12":"Dec"}' />
                        <s:set name="currentMonth" value="%{chargeMonth}" />
                        <select name="chargeMonth"class="styled">
                            <option value=" ">-- Select Expiration Month --</option>
                            <s:iterator value="#monthMap" id="month">
                                <option value="<s:property value='key'/>"
                                        <s:if test="%{key==#currentMonth}">
                                            selected="selected"
                                        </s:if>
                                        >
                                    <s:property value='value'/>
                                </option>
                            </s:iterator>
                        </select>

<span style="font-size: small;"><s:set name="monthMap" value='#{"1":"Jan","2":"Feb","3":"Mar","4":"Apr","5":"May","6":"Jun","7":"Jul","8":"Aug","9":"Sep","10":"Oct","11":"Nov","12":"Dec"}' />
<s:set name="currentMonth" value="%{chargeMonth}" />
    <select name="chargeMonth"class="styled">
    <option value=" ">-- Select Expiration Month --</option>
    <s:iterator value="#monthMap" id="month">
    <option value="<s:property value='key'/>"
        <s:if test="%{key==#currentMonth}">
        selected="selected"
        </s:if>
        >
        <s:property value='value'/>
    </option>
    </s:iterator>
    </select>
</span>

<s:set name="monthMap" value='#{"1":"Jan","2":"Feb","3":"Mar","4":"Apr","5":"May","6":"Jun","7":"Jul","8":"Aug","9":"Sep","10":"Oct","11":"Nov","12":"Dec"}' /><s:set name="currentMonth" value="%{chargeMonth}" /><select name="chargeMonth"  class="styled"><option value=" ">-- Select Expiration Month --</option><s:iterator value="#monthMap" id="month"><option value="<s:property value='key'/>"<s:if test="%{key==#currentMonth}">selected="selected"</s:if>><s:property value='value'/></option></s:iterator></select>

 

 

http://blog.csdn.net/cuker919/article/details/5181286