I had similar problems after upgrading Struts to 2.3.20. Check in your dependency hierarchy if you have any dependency to asm or cglib.
For my cases, I had some dependencies to older versions of these libs, and i had to exclude some transitive dependencies in my pom.xml: <exclusions> <exclusion> <groupId>cglib</groupId> <artifactId>cglib</artifactId> </exclusion> <exclusions> and/or <exclusions> <exclusion> <groupId>asm</groupId> <artifactId>asm</artifactId> </exclusion> <exclusions> or either use a version of cglib without dependency of asm: <dependency> <groupId>cglib</groupId> <artifactId>cglib-nodep</artifactId> <version>2.2.2</version> </dependency> Note that maybe it is not sufficient to explicitly use the version of asm which Struts 2.3.20 depends on (5.0.2), as the groupid of the asm lib was renamed from asm (in older versions) to org.ow2.asm (in newer versions). If this is your case, you have to exclude the transitive dependencies as I mentioned above. See: http://mvnrepository.com/artifact/asm/asm http://mvnrepository.com/artifact/org.ow2.asm/asm Cheers, Bruno
