thanks, jluehe:
The problem is finally solved. I've performed a double check through all ext or endorsed directories, and found that there is a special file named "servlet-api.jar.old" in my JAVA_HOME/jre/lib/ext directories. It looks like that the non-jar extension file does not affect compile time behavior but it does change runtime behavior.
After removing that ".old" file, the admin console runs normally without error.
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