今天有点心血来潮，突然想自己整个struts的应用学习一下，于是拿来前阵子买的《精通struts：基于MVC的Java Web设计与开发》，看到第二章，有个非常简单的例子，因此觉得拿来上手。
启动tomcat5.0.19，在地址栏输入http://localhost:8080/helloapp/，
错误信息如下：
org.apache.jasper.JasperException:Unable to compile class for JSP
No Java compiler was found to compile
the generated source for the JSP.
This can usually be solved by copying manually
$JAVA_HOME/lib/tools.jar from the JDK
to the common/lib directory of the Tomcat server,
followed by a Tomcat restart.
If using an alternate Java compiler,
please check its installation and access path...
开始查找原因，设置了环境变量后，重新启动了tomcat，结果错误依旧，痛苦万分~
上google，果然好用，一下就找到了解决方法：
1. Make sure the following environment variables are set correctly:
>>> JAVA_HOME points to "C:\j2sdk1.4.2" (correct folder if changed)
>>> CLASSPATH points to %JAVA_HOME%\lib
>>> PATH points to %JAVA_HOME%\bin
2. copy $JAVA_HOME/lib/tools.jar to the common/lib directory of the Tomcat server
3. Update your registry to reflect the new JVM location:
key: HKEY_LOCAL_MACHINE/SYSTEM/ControlSet001/Services/Apache
Tomcat/Parameters/JVM Library
value: C:\j2sdk1.4.2\jre\bin\server\jvm.dll
