set标签注意的地方

set标签是将某个值放到指定范围内， 好比说 student.teacher.parent.age 每次访问这个属性不只性能低，并且代码可读性不好，为了解决这个问题，能够将这个值设置为一个新值，而且放入指定范围内 
name 是必填属性，是从新生成的新变量的名字 
scope 可选属性，指定新变量被放置的范围，能够接受application,session,request,page,action 这5个值 没有指定默认是Stack Context中 
value 可选属性，指定变量的值 若是没有指定，使用ValueStack栈顶的值赋给新变量 
id 可选属性，指定新元素的引用ID 

下面是个例子： 

<!-- 使用bean标签订义一个javaBean实例--!> 
<s:bean name="lee.Person" id="p"> 
<s:param name="name" value="zhangsan"/> 
<s:param name="age" value="29"/> 
</s:bean> 
将p放入默认范围内 
<s:set value="#p" name="test"/> 
<s:property value="#test.name"/> <br> 
<s:property value="#test.age"/> <br> 
将p放入application范围内。 
<s:set value="#p" name="test" scope="application"/> 
<s:property value="#attr.test.name"/> <br> 
<s:property value="#attr.test.age"/> <br> 
将p放入session范围内。 
<s:set value="#p" name="test" scope="session"/> 
${sessionScope.test.name} <br> 
${sessionScope.test.age} <br>

这里发现一个struts2 s标签问题，<s:set value="jkadf1213" name="test"/> $｛test｝发现了获取不到值，value="'jkadf1213'" 若是是字符串的话，在双引号里面还要加单引号才能获取到值。

 

关于struts2里面s:set 和s:if的问题，

<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'}" />

这么是正确的，可是咱们set一个map，这样就不行了： 

<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，前面必需要加一个#，感受很奇怪，我也不知道为何，但愿研究过源码的给一个解答。 

<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>

发现这样不行，后来通过我反复的测试，当选择10，11，12时候能正确的将selected加上，可是选择前面的数字怎么都不行，后来经我观察，前面我将字符串用的是’，估计在后台反射的时候将其类型错误的转化成char类型了，可是估计当判断length大于1的时候，将其转化成字符串了，因此可以正确。不知道我这么猜的对不对，贴出来分享一下吧，之后但愿这样的问题不能在犯了。 
我修改成下面的就能够了： 

<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