在使用JBPM框架开发时，出现如下异常：
javax.servlet.ServletException: java.lang.LinkageError: loaderconstraint violation: when resolving interface method"javax.servlet.jsp.JspApplicationContext.getExpressionFactory()Ljavax/el/ExpressionFactory;"the class loader (instance oforg/apache/jasper/servlet/JasperLoader) of the current class,org/apache/jsp/index_jsp, and the class loader (instance oforg/apache/catalina/loader/StandardClassLoader) for resolved class,javax/servlet/jsp/JspApplicationContext, have different Classobjects for the type javax/el/ExpressionFactory used in thesignature
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:275)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
原因是，在jbpm底下的包出现冲突，我发现去掉这个包：juel-api.jar，就不会有问题了.
(也有人说去掉：juel-api.jar, juel-engine.jar, juel-impl.jar)
