struts标签使用举例--logic篇

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原文发表地址：http://www.javah.net/Struts/20070505/740.html

 <wbr>

1. <wbr> logic:empty

 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>该标签是用来判断是否为空的。如果为空，该标签体中嵌入的内容就会被处理。该标签用于以下情况：

 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>1）当Java对象为null时；

 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>2）当String对象为""时；

<wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>3）当java.util.Collection对象中的isEmpty()返回true时；

 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>4）当java.util.Map对象中的isEmpty()返回true时。
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>eg. <wbr>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><logic:empty  <wbr> name="userList"> <wbr> <wbr> <wbr>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>... <wbr> <wbr> <wbr>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> </logic:empty> <wbr>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>该句等同于：
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> if  <wbr> (userList.isEmpty())  <wbr> { <wbr> <wbr> <wbr>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>... <wbr> <wbr> <wbr>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>} <wbr> <wbr> <wbr>
 <wbr> <wbr> 2. <wbr> logic:notEmpty
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> 该标签的应用正好和logic:empty标签相反，略。
 <wbr> <wbr> 3. logic:equal
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> 该标签为等于比较符。
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> eg1. <wbr>比较用户的状态属性是否1，若为1，输出"启用";
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><logic:equal  <wbr> name="user"  <wbr> property="state"  <wbr> value="1">
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> 启用
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> </logic:equal>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> eg2. <wbr>如果上例中的value值是动态获得的，例如需要通过bean:write输出，因struts不支持标签嵌套，可采用EL来解决该问题。
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><logic:equal  <wbr> name="charge"  <wbr> property="num"  <wbr> value="${business.num}"> <wbr> <wbr> 
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> ......
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> </logic:equal>
 <wbr> <wbr> <wbr> <wbr>4. logic:notEqual
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>该标签意义与logic:equal相反，使用方法类似，略。
 <wbr> <wbr> <wbr> <wbr>5. logic:forward
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> 该标签用于实现页面导向，查找配置文件的全局forward。
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> eg. <logic:forward name="index"/>
 <wbr> <wbr> <wbr> 6. logic:greaterEqual
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> 为大于等于比较符。
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> eg. <wbr>当某学生的成绩大于等于90时，输出“优秀”：
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <logic:greaterEqual name="student" property="score" value="90">
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>优秀
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr></logic:greaterEqual>
 <wbr> <wbr> <wbr> 7. logic:greaterThan
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> 此为大于比较符，使用方法同logic:greaterEqual，略;
 <wbr> <wbr> <wbr> 8. logic:lessEqual
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> 此为小于等于比较符，使用方法同logic:greaterEqual,略;
 <wbr> <wbr> <wbr> 9. logic:lessThan
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> 此为小于比较符，使用方法同logic:greaterEqual,略;
 <wbr> <wbr> <wbr> 10. logic:match
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> 此标签比较对象是否相等；
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> eg1. 检查在request范围内的name属性是否包含"amigo"串： <wbr>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><logic:match name="name" scope="request" value="amigo">
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><bean:write name="name"/>中有一个“amigo”串。
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr></logic:match>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> eg2. 检查在request范围内的name属性是否已“amigo”作为起始字符串：
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <logic:match name="name" scope="request" value="amigo" location="start">
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><bean:write name="name"/>以“amigo”作为起始字符串。
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr></logic:match>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> eg3. <wbr>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><logic:match header="user-agent" value="Windows">
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>你运行的是Windows系统
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr></logic:match>
 <wbr> <wbr> <wbr> 11.  <wbr>logic:notMatch

 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> 此标签用于比较对象是否不相同，与logic:match意义相反，使用方法类似，略。
 <wbr> <wbr> <wbr> <wbr> 12. logic:messagePresent
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> 该标签用于判断ActionMessages/ActionErrors对象是否存在；
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> eg. <wbr>如果存在error信息，将其全部输出：
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <logic:messagePresent property="error"> <wbr>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><html:messages property="error" id="errMsg" > <wbr>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><bean:write name="errMsg"/> <wbr>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr></html:messages> <wbr> <wbr> <wbr>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr></logic:messagePresent >
 <wbr> <wbr> <wbr> <wbr> <wbr>13. logic:messagesNotPresent
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> 该标签用于判断ActionMessages/ActionErrors对象是否不存在,使用方法与logic:messagePresent类似，略
 <wbr> <wbr> <wbr> <wbr> <wbr> 14. logic:present
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> 此标签用于判断request对象传递参数是否存在。
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>  <wbr>eg1. user对象和它的name属性在request中都存在时，输出相应字符串：
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <logic:present name="user" property="name">
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>user对象和该对象的name属性都存在
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr></logic:present> 
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> eg2. 若有一个名字为“user”的JavaBean，输出对应字符串：
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <logic:present name="user" >
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>有一个名字为“user”的JavaBean。
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr></logic:present>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>eg3. <wbr>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><logic:present header="user-agent">
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>we got a user-agent header.
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr></logic:present>
 <wbr> <wbr> <wbr> <wbr> <wbr> 15. logic:notPresent
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> 此标签用于判断request对象传递参数是否不存在，意义与了logic:present相反，使用方法类似，略。
 <wbr> <wbr> <wbr> <wbr> <wbr> 16. logic:redirect
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> 该标签用于实现页面转向，可传递参数。
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> eg1. <logic:redirect href="http://www.chinaitlab.com"/>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr>17. logic:iterator
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> 用于显示列表为collection的值（List ,ArrayList,HashMap等）。
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> eg1. <wbr>逐一输出用户列表(userlList)中用户的姓名：
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><logic:iterate <wbr> id="user" name="userList">
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><bean:write name="user" property="name"/><br>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> </logic:iterate>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> eg2. <wbr>从用户列表中输出从1开始的两个用户的姓名
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><logic:iterate <wbr> id="user" name="userList" indexId="index" <wbr> offset="1" length="2">
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><bean:write name="index"/>.<bean:write name="user" property="name"/><br>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr></logic:iterate>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> eg3. logic:iterator标签的嵌套举例
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <logic:iterate id="user" indexId="index" name="userList">
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><bean:write name="index"/>. <bean:write name="user" property="name"/><br>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><logic:iterate id="address" name="user" property="addressList" length="3" offset="1">
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr><bean:write name="address"/><br>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr></logic:iterate>
 <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr> <wbr></logic:iterate>