Tomcat5与Tomcat6的EL冲突，JSTL的版本问题

正在开发的程序在Tomcat6下运行得好好的，一拷贝到Tomcat5就出错了

Servlet.service() for servlet jsp threw exception

java.lang.NoClassDefFoundError: javax/el/ELException

at java.lang.Class.getDeclaredMethods0(Native Method)

at java.lang.Class.privateGetDeclaredMethods(Class.java:2365)

at java.lang.Class.getDeclaredMethods(Class.java:1763)

at java.beans.Introspector$1.run(Introspector.java:1259)

at java.security.AccessController.doPrivileged(Native Method)

at java.beans.Introspector.getPublicDeclaredMethods(Introspector.java:1257)

at java.beans.Introspector.getTargetMethodInfo(Introspector.java:1125)

at java.beans.Introspector.getBeanInfo(Introspector.java:383)

at java.beans.Introspector.getBeanInfo(Introspector.java:155)

at java.beans.Introspector.getBeanInfo(Introspector.java:216)

at java.beans.Introspector.<init>(Introspector.java:364)

at java.beans.Introspector.getBeanInfo(Introspector.java:155)

at org.apache.jasper.compiler.Generator$TagHandlerInfo.<init>(Generator.java:3673)

at org.apache.jasper.compiler.Generator$GenerateVisitor.getTagHandlerInfo(Generator.java:2092)

at org.apache.jasper.compiler.Generator$GenerateVisitor.visit(Generator.java:1573)

at org.apache.jasper.compiler.Node$CustomTag.accept(Node.java:1441)

at org.apache.jasper.compiler.Node$Nodes.visit(Node.java:2163)

at org.apache.jasper.compiler.Node$Visitor.visitBody(Node.java:2213)

at org.apache.jasper.compiler.Node$Visitor.visit(Node.java:2219)

这个问题应该是出在JSTL的支持上，通过查看，原来系统使用了JSTL1.2。再进一步到网上查看相关资料，发现：

The JSTL 1.2 Maintenace Release aligns with the Unified Expression Language (EL) that is being delivered as part of the JavaServer Pages (JSP) 2.1 specification。JSTL 1.2 is part of the Java EE 5 platform. （from http://java.sun.com/products/jsp/jstl/）

Jakarta Taglibs hosts the Standard Taglib 1.1, an implementation of the JSP Standard Tag Library (JSTL), version 1.1, which was developed under the Java Community Process.

NOTE: Standard-1.1 (JSTL 1.1) requires a JSP container that supports the Java Servlet 2.4 and JavaServer Pages 2.0 specifications. Jakarta Tomcat 5 supports the new specifications. The Standard-1.1 taglib has been tested with Tomcat 5.0.3.

Standard-1.0 (implementation of the JSTL 1.0 specification) requires a JSP container that supports the Java Servlet 2.3 and JavaServer Pages 1.2 specifications. Jakarta Tomcat 4 supports these specifications. The Standard 1.0 taglib has been tested with Tomcat 4.1.24. (from http://jakarta.apache.org/taglibs/doc/standard-doc/intro.html)

Tomcat6 实现了 servlet 2.5 和JSP2.1的规范，可以支持JSTL1.2；而Tomcat5实现了 servlet 2.4 和JSP2.0的规范，只能支持JSTL1.1

所以，只要使用JSTL1.1(standard-1.1.jar和jstl-1.1.jar)替换JSTL1.2（jstl-1.2.jar）即可在Tomcat5下正常运行！另外，web.xml必须指定使用servlet 2.4 和JSP2.0的规范：

<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">