Steps to Reproduce

1. put attached jar into your project
2. load the zul

Current Result

java.lang.ClassCastException: de.odysseus.el.ExpressionFactoryImpl cannot be cast to org.zkoss.zel.ExpressionFactory
at org.zkoss.zel.ExpressionFactory.newInstance(ExpressionFactory.java:187) ~[zel-8.0.2.1-Eval.jar:8.0.2.1]
at org.zkoss.zel.ExpressionFactory.newInstance(ExpressionFactory.java:106) ~[zel-8.0.2.1-Eval.jar:8.0.2.1]
at org.zkoss.zel.Util.getExpressionFactory(Util.java:126) ~[zel-8.0.2.1-Eval.jar:8.0.2.1]

Expected Result

no error

Root Cause

In org.zkoss.zel.ExpressionFactory.discoverClassName(), it gets a class name from service API first getClassNameServices(), so it will get de.odysseus.el.ExpressionFactoryImpl from juel-spi-2.2.7.jar.
Since org.zkoss.zel.ExpressionFactory is not a Java EE standard class, no standard implementation can be cast into it. Hence, get a class name from service API might not get something useful.

Workaround

• remove className = getClassNameServices(tccl); and override ExpressionFactory