c 标签

1 . c：out  -- Like <%= ... >, but for expressions. =out.println(String)

<c:out value="hello world!" default="" escapeXml=""></c:out>

attribute	description
value	Expression to be evaluated. required：true rtexprvalue：true
default	Default value if the resulting value is null. required：false rtexprvalue：true
escapeXml	Determines whether characters <,>,&,'," in the resulting string should be converted to their corresponding character entity codes. Default value is true.(是否按纯文本显示value的值，默认true，此时不能识别HTML标签；设为false时可以识别HTML标签) required：false rtexprvalue：true

等价于<% out.println("hello world!");%>

用于输出内容，如何输入域对象中的内容呢？（request,session,application,pageContext）

     <%

          request.setAttribute("a", "你好1"); 

          session.setAttribute("a", "你好2"); 

          application.setAttribute("a", "你好3"); 

          pageContext.setAttribute("a", "你好4"); 

      %>

    <c:out value="${a}" default="null value." escapeXml=""></c:out>

${a} 域对象中存在属性名相同时，搜索的顺序(优先级)：pageContext > request > session > application，顾输出：你好4

获取对象（User有两个属性：uname,pwd）：

      <%

          User user = new User();

          user.setUname("zfq");

          user.setPwd("123");

          session.setAttribute("u", user);

       %>

    <!-- User的uanme和pwd必须有get方法 -->

    <c:out value="${u.uname}" default="null value." escapeXml="false"></c:out>

    <c:out value="${u.pwd}" default="null value." escapeXml="false"></c:out>

    ${u.uname }  ${u.pwd }    <!-- el表达式,可在里面做运算 -->

 

2.c：set --Sets the result of an expression evaluation in a 'scope'. =setAttribute(String,Object)

<c:set property="" value="中国" scope="request" target="" var="china"></c:set>

<c:set property="" value="中国1" scope="session" target="" var="china"></c:set>

<c:out value="${china }"></c:out>

输出：中国

c:set执行的内容多在控制器中就完成了，所以该标签用的时候不多

attribute	description
var	Name of the exported scoped variable to hold the value specified in the action. The type of the scoped variable is whatever type the value expression evaluates to. required：false rtexprvalue：false
value	Expression to be evaluated. required：false rtexprvalue：true
target	Target object whose property will be set. Must evaluate to a JavaBeans object with setter property property, or to a java.util.Map object. required：false rtexprvalue：true
property	Name of the property to be set in the target object. required：false rtexprvalue：true
scope	Scope for var.（request/session） 不能是application和pageContext (指定域对象,默认) required：false rtexprvalue：false

 

3.c：remove  -- Removes a scoped variable (from a particular scope, if specified).=removeAttribute(String,Object)

<%request.setAttribute("attr", "Hello"); %>

<c:out value="${attr }"></c:out><br>

<c:remove var="attr" scope="request"/>

<c:out value="${attr }" default="null value"></c:out>

输出：Hello
      null value

attribute	description
var	Name of the scoped variable to be removed. required：true rtexprvalue：false
scope	Scope for var.未指明则删除所有域对象的内容 required：false rtexprvalue：false

 

4. c:catch  -- Catches any Throwable that occurs in its body and optionally exposes it.

<c:catch var="myException">

        <%  

           int i = 8/0; 

        %>

    </c:catch>

    <c:out value="${myException.message }"></c:out>

输出：/ by zero

attribute	description
var	Name of the exported scoped variable for the exception thrown from a nested action. The type of the scoped variable is the type of the exception thrown. required：false rtexprvalue：false

 

5. c:if  -- Simple conditional tag, which evalutes its body if the supplied condition is true and optionally exposes a Boolean scripting variable representing the evaluation of this condition

       <%

          request.setAttribute("attr", "zfq");

          request.setAttribute("num", "25");

       %>

       <c:if test="${attr=='zfq'}" var="cif" scope="session">

           <c:out value="ok"></c:out>

       </c:if>

       <br>

       <c:if test="${cif }">

           <c:out value="not ok"></c:out>

       </c:if>

       <br>

       <c:if test="${num > 12 }">

           <c:out value="num > 12"></c:out>

       </c:if>

输出：ok

      not ok

      num > 12

attribute	description
test	The test condition that determines whether or not the body content should be processed. required：true rtexprvalue：true type:boolean
var	Name of the exported scoped variable for the resulting value of the test condition. The type of the scoped variable is Boolean. (把判断结果(bool值)放入域对象) required：false rtexprvalue：false
scope	Scope for var. required：false rtexprvalue：false

 

6. c:choose -- Simple conditional tag that establishes a context for mutually exclusive conditional operations, marked by <when> and <otherwise>

 

attribute	description
null	null

 

7. c:when -- Subtag of <choose> that includes its body if its condition evalutes to 'true'

 

attribute	description
test	The test condition that determines whether or not the body content should be processed. required：true rtexprvalue：true type:boolean

 

8. c:otherwise -- Subtag of <choose> that follows <when> tags and runs only if all of the prior conditions evaluated to 'false'

 

attribute	description
null	null

 

6、7、8例子：

     <%

        Rat rat = new Rat();

        rat.setName("Jerry");

        rat.setAge(21);

        request.setAttribute("rat", rat);

     %>

      <c:choose>

     <c:when test="${rat.age <= 1 }"> <font color="red">老鼠太小不能吃！</font> </c:when>

     <c:when test="${rat.age > 1 and rat.age <= 4}"> <font color="green">老鼠正在适吃年龄！</font> </c:when>

     <c:when test="${rat.age > 4 and rat.age <= 20 }"> <font color="red">老鼠太老不好吃！</font> </c:when>

     <c:otherwise><font color="red">老鼠已成精，敢吃吗？</font></c:otherwise>

    </c:choose>

输出：老鼠已成精，敢吃吗？

 

9. c:foreach -- The basic iteration tag, accepting many different collection types and supporting subsetting and other functionality

    <%

        ArrayList<Rat> rats = new ArrayList<Rat>();

        for(int i = 0;i < 5;i++){

            Rat rat = new Rat();

            rat.setAge(i+1);

            rat.setName("rat"+(i+1));

            rats.add(rat);

        }

        request.setAttribute("attr_rats", rats);

     %>

    <c:forEach begin="0" end="4" items="${attr_rats}" step="1" var="rat" varStatus="">

        <c:out value="${rat.name }    ${rat.age }"></c:out><br>

    </c:forEach>

输出：rat1 1
      rat2 2
      rat3 3
      rat4 4
      rat5 5

attribute	description
items	Collection of items to iterate over. required：false rtexprvalue：true type:java.lang.Object deferred-value:java.lang.Object
begin	If items specified: Iteration begins at the item located at the specified index. First item of the collection has index 0. If items not specified: Iteration begins with index set at the value specified. required：false rtexprvalue：true type:int
end	If items specified: Iteration ends at the item located at the specified index (inclusive). If items not specified: Iteration ends when index reaches the value specified. required：false rtexprvalue：true type:int
step	Iteration will only process every step items of the collection, starting with the first one. required：false rtexprvalue：true type:int
var	Name of the exported scoped variable for the current item of the iteration. This scoped variable has nested visibility. Its type depends on the object of the underlying collection. required：false rtexprvalue：false
varStatus	Name of the exported scoped variable for the status of the iteration. Object exported is of type javax.servlet.jsp.jstl.core.LoopTagStatus. This scoped variable has nested visibility. required：false rtexprvalue：false

 

10. c:forTokens -- Iterates over tokens, separated by the supplied delimeters(分界符)

       <%

          String s = "a,b,c";

          request.setAttribute("str", s);

       %>

      

    <c:forTokens items="${str }" delims="," var="c">

        ${c}

    </c:forTokens>

输出：a b c

attribute	description
items	String of tokens to iterate over. required：true rtexprvalue：true type:java.lang.String deferred-value:java.lang.String
delims	The set of delimiters (the characters that separate the tokens in the string). required：true rtexprvalue：true type:java.lang.String
begin	Iteration begins at the token located at the specified index. First token has index 0. required：false rtexprvalue：true type:int
end	Iteration ends at the token located at the specified index (inclusive). required：false rtexprvalue：true type:int
step	Iteration will only process every step tokens of the string, starting with the first one. required：false rtexprvalue：true type:int
var	Name of the exported scoped variable for the current item of the iteration. This scoped variable has nested visibility. required：false rtexprvalue：false
varStatus	Name of the exported scoped variable for the status of the iteration. Object exported is of type javax.servlet.jsp.jstl.core.LoopTag Status. This scoped variable has nested visibility. required：false rtexprvalue：false

 

 

 

 

 

11. c:redirect -- Redirects to a new URL.

<c:redirect context="" url="http://www.baidu.com"></c:redirect>

跳转到百度首页

attribute	description
url	The URL of the resource to redirect to. required：false rtexprvalue：true
context	Name of the context when redirecting to a relative URL resource that belongs to a foreign context. required：false rtexprvalue：true

 

12. c:import -- Retrieves an absolute or relative URL and exposes its contents to either the page, a String in 'var', or a Reader in 'varReader'.

        <c:import url="../a.jsp">

            <c:param name="uname" value="zfq"></c:param>

        </c:import>

      JSP页面中访问参数：       

        <body>

            A jsp page.<br>

            ${param.uname}

        </body>

attribute	description
url	The URL of the resource to import. required：true rtexprvalue：true
var	Name of the exported scoped variable for the resource's content. The type of the scoped variable is String. required：false rtexprvalue：false
scope	Scope for var. required：false rtexprvalue：false
varReader	Name of the exported scoped variable for the resource's content. The type of the scoped variable is Reader. required：false rtexprvalue：false
context	Name of the context when accessing a relative URL resource that belongs to a foreign context. required：false rtexprvalue：true
charEncoding	Character encoding of the content at the input resource. required：false rtexprvalue：true

 

13. c:url -- Creates a URL with optional query parameters.

 

attribute	description
var	Name of the exported scoped variable for the processed url. The type of the scoped variable is String. required：false rtexprvalue：false
scope	Scope for var. required：false rtexprvalue：false
value	URL to be processed. required：false rtexprvalue：true
context	Name of the context when specifying a relative URL resource that belongs to a foreign context. required：false rtexprvalue：true

 

14. c:param -- Adds a parameter to a containing 'import' tag's URL.

 

attribute	description
name	Name of the query string parameter. required：true rtexprvalue：true
value	Value of the parameter. required：false rtexprvalue：true

 

注解：

（1）rtexprvalue的全称是 Run-time Expression Value， 它用于表示是否能够利用JSP表达式

来自为知笔记(Wiz)