java.lang.LinkageError: loader constraint violation: when resolving interface method "javax.servlet.

严重: 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 这个错误！

原因是项目中WEB-INF\lib中的三个jar包(juel.jar, juel-engine.jar, juel-impl.jar)和tomcat6下lib中jar包(el-api.jar)冲突

解决方法：

     将juel.jar, juel-engine.jar, juel-impl.jar这三个包复制到tomcat6下lib中，并删除原来的el-api.jar，

切记要把WEB-INF\lib中的juel.jar, juel-engine.jar, juel-impl.jar删除。不然还是要冲突。