JSP 中无法使用EL表达式原因-优快云博客

本文探讨了在使用JSP与PagerTagLibrary时遇到的问题：当属性值为变量时出现NumberFormatException错误。通过调整页面配置，设置isELIgnored属性为false，解决了表达式语言（EL）在JSTL标签外部的评估问题。

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Hello to all from Spain

Well, my problem is:

I use JSP, LE and a tag library called "Pager Tag Library".
I have a .jsp page with this:


<c:set var="varbool" value="false"/>

<pg:pager items="<%= varNumFilas.intValue() %>"
url="consultatit.do"
index="center"
maxPageItems="5"
maxIndexPages="5"
isOffset="${varbool}"
export="offset,currentPageNumber=pageNumber"
scope="request">

This code works well. No problem. But with...

<c:set var="varNumFilas" value="15"/>
<c:set var="maxpages" value="5"/>

<pg:pager items="${varNumFilas}"
url="consultatit.do"
index="center"
maxPageItems="5"
maxIndexPages="${maxpages}"
isOffset="false"
export="offset,currentPageNumber=pageNumber"
scope="request">

I get an error:

java.lang.NumberFormatException: For input string: "${varNumFilas}"
java.lang.NumberFormatException.forInputString(Unknown Source)
java.lang.Integer.parseInt(Unknown Source)
java.lang.Integer.valueOf(Unknown Source)
org.apache.jasper.compiler.JspUtil.coerceToInt(JspUtil.java:796)
...

Always, with any variable...

That is to say, when the required value of the attribute is numeric there is an error, and when the required value is not numeric (an String) there is not an error... ?Why?

Thanks to all

_______________
solve:

So the question is, what server/JSP spec are you using?

If you are using Tomcat 5.x or JSP2.0 spec, then you get EL evaluated outide of JSTL tags by adding:


<%@ page isELIgnored="false" %>

At the the top of the page.

If you are using an older version of Tomcat, or a server that does not support JSP 2.0, then you will have to re-write the Page Tags to be able to translate EL for you, or not use EL...