JSP pages do not compile an El expression solution __js

In JSP2.0, the addition of El language, can be used in El language, through the El language, to achieve the acquisition of data, further scriptlet code from the JSP page separate.
The El language is convenient for everyone, but sometimes you will also experience situations where El expressions cannot be displayed, and below I'll enumerate a few scenarios where El expressions can't be displayed and solutions:
1.web-inf/web.xml,web The deployment description file that is applied refers to version 2.3 or earlier of the servlet specification (that is, jsp1.2 or earlier), the jsp2.0 expression language automatically

Deactivate in, note that the version attribute inside should be 2.4 and above.
2.web.xml, whether the JSP expression language is deactivated
<jsp-property-group>
<url-pattern>/legacy/*.jsp</url-pattern>
<el-ignored>true</el-ignored>
</jsp-property-group>

The solution to this situation is to change the <el-ignored>true</el-ignored> to <el-ignored>false</el-ignored>

3. Page Deactivate JSP expression language
<%@ page iselenabled = "false"%>

Workaround: Change to <%@ page iselenabled = "true"%> (inactive El expression, false for constant El expression)