jsp中jstl标签库core全解析

首先来认识一下jstl:

jsp中jstl标签库core全解析

下面来介绍一下核心标签库：

jsp中jstl标签库core全解析

前言：jstl是用来辅助el表达式，用来在jsp页面显示复杂结构的数据

一：<c:out value="" escapeXml="" default="">:

查看c.tld可知：

<tag>
    <description>
        Like <%= ... >, but for expressions.
    </description> 
    <name>out</name>
    <tag-class>org.apache.taglibs.standard.tag.rt.core.OutTag</tag-class>
    <body-content>JSP</body-content>
    <attribute>
        <description>
Expression to be evaluated.
        </description>
        <name>value</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
    <attribute>
        <description>
Default value if the resulting value is null.
        </description>
        <name>default</name>
        <required>false</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
    <attribute>
        <description>
Determines whether characters <,>,&,'," in the
resulting string should be converted to their
corresponding character entity codes. Default value is
true.
        </description>
        <name>escapeXml</name>
        <required>false</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>

向界面输出value值（可输出特殊字符）：

属性解析： value: 输出的值（el表达式，字符串）

escapeXml:是否将特殊字符转化，默认true

default: value值为null时输出

代码示例：

<%
       pageContext.setAttribute("name", "Tom");
       pageContext.setAttribute("name2", "<font color='red'>Tom</font>");
    %>

    <c:out value="${name2}" escapeXml="true"/><br/>
    ${name2}<br/>

out会将<>解析成&qt;&gt，这样保证界面原样输出，而一般的el表达式不转化<>，hyml会解析颜色

二：<c:set property="" scope="" target="" value="" var="">

 <tag>
    <description>
        Sets the result of an expression evaluation in a 'scope'
    </description>
    <name>set</name>
    <tag-class>org.apache.taglibs.standard.tag.rt.core.SetTag</tag-class>
    <body-content>JSP</body-content>
    <attribute>
        <description>
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.
        </description>
        <name>var</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <description>
Expression to be evaluated.
        </description>
        <name>value</name>
        <required>false</required>
        <rtexprvalue>true</rtexprvalue>
        <deferred-value>
    <type>java.lang.Object</type>
        </deferred-value>
    </attribute>
    <attribute>
        <description>
Target object whose property will be set. Must evaluate to
a JavaBeans object with setter property property, or to a
java.util.Map object.
        </description>
        <name>target</name>
        <required>false</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
    <attribute>
        <description>
Name of the property to be set in the target object.
        </description>
        <name>property</name>
        <required>false</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
    <attribute>
        <description>
Scope for var.
        </description>
        <name>scope</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
  </tag>

设置属性：相当于setAttribute();

属性搭配一： var:存储容器中的属性变量名

value:属性值

属性搭配二：target:容器中的一个对象

property:对象属性名

value:属性值

scope:容器的种类（四种，二种搭配可选可不选）

代码示例：

<!-- c:set 设置属性,默认作用域:pageScope-->
    <c:set var="aa" value="abc123" />
    <c:set var="aa" value="ccc123" scope="request"/>
    ${aa}, ${requestScope.aa}

<jsp:useBean id="car" class="cn.hncu.elWeb.domain.Car"></jsp:useBean>    <c:set target="${car }" property="carno" value="No.1"></c:set>    <c:out value="${car.carno }" escapeXml="true"></c:out>

三：<c:remove var="" scope="">

<tag>
    <description>
        Removes a scoped variable (from a particular scope, if specified).
    </description>
    <name>remove</name>
    <tag-class>org.apache.taglibs.standard.tag.common.core.RemoveTag</tag-class>
    <body-content>empty</body-content>
    <attribute>
        <description>
Name of the scoped variable to be removed.
        </description>
        <name>var</name>
        <required>true</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <description>
Scope for var.
        </description>
        <name>scope</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
  </tag>

在容器中移除var值属性，默认全部容器

属性： var:容器中的属性值

scope:指定的容器

代码示例：

<!-- c:remove 删除属性,默认作用域:pageScope,request等4个容器中的都会被删除-->
     <!-- 下面这一句，若没有scope属性，则前面的所有"aa"都会被清除。写了下面的scope，则只清除指定的request中的那个"aa"属性 -->
     <c:remove var="aa" scope="request"/>
      ${aa}

四：<c:if test="" scope="" var=""></c:if>

<tag>
    <description>
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
    </description>
    <name>if</name>
    <tag-class>org.apache.taglibs.standard.tag.rt.core.IfTag</tag-class>
    <body-content>JSP</body-content>
    <attribute>
        <description>
The test condition that determines whether or
not the body content should be processed.
        </description>
        <name>test</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
<type>boolean</type>
    </attribute>
    <attribute>
        <description>
Name of the exported scoped variable for the
resulting value of the test condition. The type
of the scoped variable is Boolean.        
        </description>
        <name>var</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <description>
Scope for var.
        </description>
        <name>scope</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
  </tag>

判断test属性值真假，是否执行里面的代码

属性： test：一个返回boolean值得表达式

var：存储test返回值的变量名

scope: 存储var变量的容器

代码示例：

<!-- c:if 展示if/else-->
    <c:if test="${ lis[0].age > 10 }" var="boo" scope="session">
       dfdfdfdf

    </c:if>
    <c:if test="${!boo}">
      <h2>NOooooo</h2>
    </c:if>

五：<c:choose >
                 <c:when test=""></c:when>
     <c:otherwise></c:otherwise>
   </c:choose>

<tag>
    <description>
Simple conditional tag that establishes a context for
mutually exclusive conditional operations, marked by
<when> and <otherwise>
    </description>
    <name>choose</name>
    <tag-class>org.apache.taglibs.standard.tag.common.core.ChooseTag</tag-class>
    <body-content>JSP</body-content>
  </tag>

 <tag>    <description>Subtag of <choose> that includes its body if itscondition evalutes to 'true'    </description>    <name>when</name>    <tag-class>org.apache.taglibs.standard.tag.rt.core.WhenTag</tag-class>    <body-content>JSP</body-content>    <attribute>        <description>The test condition that determines whether or not thebody content should be processed.        </description>        <name>test</name>        <required>true</required>        <rtexprvalue>true</rtexprvalue><type>boolean</type>    </attribute>  </tag>

<tag>    <description>        Subtag of <choose> that follows <when> tags        and runs only if all of the prior conditions evaluated to        'false'    </description>    <name>otherwise</name>    <tag-class>org.apache.taglibs.standard.tag.common.core.OtherwiseTag</tag-class>    <body-content>JSP</body-content>  </tag>

一种类似于swich-case结构

<c:choose>:无属性，标记开始

<c:when>:相当于case可重复属性test:会返回为boolea值得表达式

<c:otherwise>:无属性，相当于defaule语句

代码示例：

<!-- c:choose,c:when,c:otherwise  类似Java中的switch-case-default且每项自动带break -->
      <c:set var="score" value="98" />
      <c:choose>
        <c:when test="${score>=90}">
                       优秀
        </c:when>
        <c:when test="${score>=80}">
                       良好
        </c:when>
        <c:when test="${score>=70}">
                       中等
        </c:when>
        <c:otherwise>
                       不行
        </c:otherwise>
      </c:choose>

六：普通循环：<c:forEach begin="" end="" step="" var="" varStatus=""></c:forEach>
增强for循环： <c:forEach items="" var="" varStatus=""></c:forEach>

 <tag>
    <description>
The basic iteration tag, accepting many different
        collection types and supporting subsetting and other
        functionality
    </description>
    <name>forEach</name>
    <tag-class>org.apache.taglibs.standard.tag.rt.core.ForEachTag</tag-class>
    <tei-class>org.apache.taglibs.standard.tei.ForEachTEI</tei-class>
    <body-content>JSP</body-content>
    <attribute>
        <description>
Collection of items to iterate over.
        </description>
<name>items</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
<type>java.lang.Object</type>
        <deferred-value>
    <type>java.lang.Object</type>
        </deferred-value>
    </attribute>
    <attribute>
        <description>
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.
        </description>
<name>begin</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
<type>int</type>
    </attribute>
    <attribute>
        <description>
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.
        </description>
<name>end</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
<type>int</type>
    </attribute>
    <attribute>
        <description>
Iteration will only process every step items of
the collection, starting with the first one.
        </description>
<name>step</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
<type>int</type>
    </attribute>
    <attribute>
        <description>
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.
        </description>
<name>var</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <description>
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.
        </description>
<name>varStatus</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
    </attribute>
  </tag>

第一套普通循环相当于：for( var=begin; var<=end; var+=step)
属性：begin:起始值

end:结尾值

step:步长值

var:表示目前的循环值

第二套属性搭配相当于：for( var : items )

属性：items:集合/数组的引用名

var:每一项的变量名

varStatus=""该属性可加可不加：有俩个下级变量：

index:记录当前下标值 items-var型从0开始 begin-end-step型从begin开始

count:记录当前遍历数

代码示例：

<!-- forEach的遍历功能 -->
     <%
        List list2 = new ArrayList();
     list2.add("aa1111" );
     list2.add("bb2222");
     list2.add(200);
     list2.add(100);
     request.setAttribute("lis2", list2);
     %>
     <c:forEach items="${lis2}" var="aa">
     ${aa } ,
 </c:forEach>

    <%
       Map<String,Object> map = new HashMap<String,Object>();
    map.put("name", "Rose");
    map.put("age",55);
    map.put("tel", "13566668888");
    pageContext.setAttribute("m", map);
    %>
    <br/>
    <c:forEach items="${m}" var="im">
       ${im.key} = ${im.value } <br/>
    </c:forEach>

    <%
       String strs[] ={"aaa","bbb","111","2222"};
       pageContext.setAttribute("strs", strs);
    %>
     <br/>
    <c:forEach items="${strs}" var="str">
       ${str} ,,
    </c:forEach>

    <h3>看看ForEach标签中的varStatus属性---idx.index是元素的下标(从0开始)，idx.count是元素的序号(从1开始计数)</h3>
    <c:forEach items="${strs}" var="str" varStatus="idx">
      ${str} ---- index= ${idx.index}   count= ${idx.count} <br/>
    </c:forEach>

    <!-- forEach的普通循环功能 -->
    <c:forEach begin="20" end="40" var="i" step="2" varStatus="idx">
        ${i}    --${idx.count} <br/>
    </c:forEach>

七：分隔符拆分<c:forTokens items="" delims="" var=""></c:forTokens>

从begin-end间，以step长度分割<c:forTokens begin="" end="" step="" var=""></c:forTokens>

<tag>
    <description>
Iterates over tokens, separated by the supplied delimeters
    </description>
    <name>forTokens</name>
    <tag-class>org.apache.taglibs.standard.tag.rt.core.ForTokensTag</tag-class>
    <body-content>JSP</body-content>
    <attribute>
        <description>
String of tokens to iterate over.
        </description>
<name>items</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
<type>java.lang.String</type>
        <deferred-value>
    <type>java.lang.String</type>
        </deferred-value>
    </attribute>
    <attribute>
        <description>
The set of delimiters (the characters that
separate the tokens in the string).
        </description>
<name>delims</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
<type>java.lang.String</type>
    </attribute>
    <attribute>
        <description>
Iteration begins at the token located at the
specified index. First token has index 0.
        </description>
<name>begin</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
<type>int</type>
    </attribute>
    <attribute>
        <description>
Iteration ends at the token located at the
specified index (inclusive).
        </description>
<name>end</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
<type>int</type>
    </attribute>
    <attribute>
        <description>
Iteration will only process every step tokens
of the string, starting with the first one.
        </description>
<name>step</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
<type>int</type>
    </attribute>
    <attribute>
        <description>
Name of the exported scoped variable for the
current item of the iteration. This scoped
variable has nested visibility.
        </description>
<name>var</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <description>
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.
        </description>
<name>varStatus</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
    </attribute>
  </tag>

<c:forTokens items="" delims="" var=""></c:forTokens>型：

属性：items:要分割的表达式

delims:分隔符

var:分割的每一项

代码示例：

<!-- c:forTokens 用分隔符去拆分字符串-->
      <c:forTokens items="aa,bb,cc,ok,jk23" delims="," var="str">
          ${str}  
      </c:forTokens>

八：<c:import url="" charEncoding="" context="" varReader="" scope="" var=""></c:import>相当于<jsp:include>动态导入

<tag>
    <description>
        Retrieves an absolute or relative URL and exposes its contents
        to either the page, a String in 'var', or a Reader in 'varReader'.
    </description>
    <name>import</name>
    <tag-class>org.apache.taglibs.standard.tag.rt.core.ImportTag</tag-class>
    <tei-class>org.apache.taglibs.standard.tei.ImportTEI</tei-class>
    <body-content>JSP</body-content>
    <attribute>
        <description>
The URL of the resource to import.
        </description>
        <name>url</name>
        <required>true</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
    <attribute>
        <description>
Name of the exported scoped variable for the
resource's content. The type of the scoped
variable is String.
        </description>
        <name>var</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <description>
Scope for var.
        </description>
        <name>scope</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <description>
Name of the exported scoped variable for the
resource's content. The type of the scoped
variable is Reader.
        </description>
        <name>varReader</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <description>
Name of the context when accessing a relative
URL resource that belongs to a foreign
context.
        </description>
        <name>context</name>
        <required>false</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
    <attribute>
        <description>
Character encoding of the content at the input
resource.
        </description>
        <name>charEncoding</name>
        <required>false</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>

属性：url:导入的资源路径（可访问）

代码示例：

<!-- c:import 导入资源，相当于动态包含，共享同一个request-->
     <c:import url="/jsps/b.jsp"></c:import>

九：<c:url context="" scope="" value="" var=""></c:url>链接，具有重写url技术

<tag>
    <description>
        Creates a URL with optional query parameters.
    </description>
    <name>url</name>
    <tag-class>org.apache.taglibs.standard.tag.rt.core.UrlTag</tag-class>
    <body-content>JSP</body-content>
    <attribute>
        <description>
Name of the exported scoped variable for the
processed url. The type of the scoped variable is
String.
        </description>
        <name>var</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <description>
Scope for var.
        </description>
        <name>scope</name>
        <required>false</required>
        <rtexprvalue>false</rtexprvalue>
    </attribute>
    <attribute>
        <description>
URL to be processed.
        </description>
        <name>value</name>
        <required>false</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
    <attribute>
        <description>
Name of the context when specifying a relative URL
resource that belongs to a foreign context.
        </description>
        <name>context</name>
        <required>false</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>

属性：value:资源路径（可访问）

代码示例

<a href="<c:url value='/jsps/i18n.jsp'/>">I18N演示</a>

十：<c:redirect context="" url=""></c:redirect>重定向

<tag>
    <description>
        Redirects to a new URL.
    </description>
    <name>redirect</name>
    <tag-class>org.apache.taglibs.standard.tag.rt.core.RedirectTag</tag-class>
    <body-content>JSP</body-content>
    <attribute>
        <description>
The URL of the resource to redirect to.
        </description>
        <name>url</name>
        <required>false</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
    <attribute>
        <description>
Name of the context when redirecting to a relative URL
resource that belongs to a foreign context.
        </description>
        <name>context</name>
        <required>false</required>
        <rtexprvalue>true</rtexprvalue>
    </attribute>
  </tag>

属性：url:资源路径（可访问）

代码示例

<!-- c:redirect 重定向，相当于response.sendRedirect(...) -->
     <%-- 
         <c:redirect url="/jsps/aa.jsp"></c:redirect>
      --%>

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