org.apache.jasper.JasperException异常的原因

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.

这个异常一般是

1- jsp文件编写错误，里面可能包含错误的代码。
2 - 是你的jdk没有配置好。环境变量或路径设置不对。
还有，用浏览器打开：http://localhost:8080
如果出现提示成功画面，那说明八成是JSP文件有问题。
一般要把jsp文件放在ROOT目录下才可以正常运行。