嚴重: Servlet.service() for servlet jsp threw exception
java.lang.LinkageError: loader constraint violation: when resolving interface method

"javax.servlet.jsp.JspApplicationContext.getExpressionFactory()Ljavax/el/ExpressionFactory;" the class loader (instance of

org/apache/jasper/servlet/JasperLoader) of the current class, org/apache/jsp/index_jsp, and the class loader (instance of

org/apache/catalina/loader/StandardClassLoader) for resolved class, javax/servlet/jsp/JspApplicationContext, have different

Class objects for the type javax/el/ExpressionFactory used in the signature

原因：

jbpm4 在tomcat6 下面ssh2 這個錯誤！

原因是專案中WEB-INF\lib中的三個jar包(juel.jar, juel-engine.jar, juel-impl.jar)和tomcat6下lib中jar包(el-api.jar)衝突

解決方法：

     將juel.jar, juel-engine.jar, juel-impl.jar這三個包複製到tomcat6下lib中，並刪除原來的el-api.jar，

切記要把WEB-INF\lib中的juel.jar, juel-engine.jar, juel-impl.jar刪除。不然還是要衝突。