//EL  的基本用法
類型            | 示例                         | 對(duì)應(yīng)的調(diào)用方法
javaBeans    | ${user.username}*    | user.getUsername()
                    | ${user["username"]}  |
                    | ${user['username']}   | sport[1]
數(shù)組            | ${sport[1]}*             |
                    | ${sport['1']}              |
                    | ${sport["1"]}             |
List              | ${address[2]}*          | address.get(2)
                    | ${address['2']}          |
                    | ${address["2"]}         |
Map             | ${phone["home"]}     | phone.get("home")
                    | ${phone['home']}      |
                    | ${phone.home}*       |
           
//EL的內(nèi)置對(duì)象（與JSP有區(qū)加別，只能在EL中使用，不能用在JSP中,名稱不同但指同一個(gè)內(nèi)容）
pageContext      對(duì)應(yīng)JSP中當(dāng)前頁(yè)面上下文的對(duì)象
pageScope        對(duì)應(yīng)JSP中page對(duì)象
requestScope     對(duì)應(yīng)JSP中request對(duì)象
sessionScope     對(duì)應(yīng)JSP中session對(duì)象
applicationScope 對(duì)應(yīng)JSP中application對(duì)象
param            對(duì)應(yīng)頁(yè)面?zhèn)髦档膶?duì)象
paramValues      對(duì)應(yīng)頁(yè)面?zhèn)鱽?lái)一組值的對(duì)象
header           對(duì)應(yīng)頁(yè)面頭信息的值對(duì)象
headerValues     對(duì)應(yīng)頁(yè)面頭信息的數(shù)組對(duì)象
<%= session.getAttribute("phone")%>
等價(jià)于:
${sessionScope.phone}
cookie對(duì)應(yīng)cookie對(duì)象的值
initParam對(duì)應(yīng)設(shè)定的初始參數(shù)的值

//設(shè)定JSP不使用JSP EL
當(dāng)前面頁(yè)不使用
<%@page isELIgnored="true"%>
整個(gè)WEB應(yīng)用不使用JSP EL
修改web.xml
<web-app...>
  <jsp-config>
    <jsp-property-group>
      <url-pattern>*.jsp</url-pattern>
      <el-ignored>true</el-ignored>
    </jsp-property-group>
  </jsp-config>
</web-app>
----------------------------------------------------
pageContext.setAttribute("username",null)//false
pageContext.setAttribute("username","")//false

${empty username}//判斷username是否為空
---------------------------------------------------
pageContext.setAttribute("username","janly")
request.setAttribute("username","janly")
session.setAttribute("username","janly")
application.setAttribute("username","janly")

${pageScope.username}
${requestScope.username}
${sessionScope.username}
${applicationScope.username}
${username}按作用域范圍找查
-----------------------------------------
web.xml
<context-param>
<param-name>repeat</param-name>
<param-value>100</param-value>
</context-param>

${initParam.repeat}
${param.username}
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