Struts Start Error javassist library is missing

Long time no struts2, recently in the configuration, start the server error

caused by:java.lang.ExceptionInInitializerError at Com.opensymphony.xwork2.ognl.OgnlValueStackFactory.setContainer (Ognlvaluestackfactory.java:84)    ... 64morecaused by:java.lang.IllegalArgumentException:Javassist Library is missing in Classpath! Please add missed dependency!At Ognl. Ognlruntime.<clinit> (ognlruntime.java:168)    ... 65morecaused by:java.lang.ClassNotFoundException:javassist. Classpool at Org.apache.catalina.loader.WebappClassLoader.loadClass (Webappclassloader.java:1680) at Org.apache.catalina.loader.WebappClassLoader.loadClass (Webappclassloader.java:1526) at Java.lang.ClassLoader.loadClassInternal (Classloader.java:320At JAVA.LANG.CLASS.FORNAME0 (Native Method) at Java.lang.Class.forName (Class.java:169) at OGNL. Ognlruntime.<clinit> (ognlruntime.java:165)    ... More

My struts2 is 2.3.20 is a very new version.

See description is missing such a dependency: Java.lang.IllegalArgumentException:Javassist library is missing in classpath! Please add missed dependency! This dependent name is called Javassist this is because Xwork migrated to Apache after the use of the new OGNL 3.x, the new OGNL 3.x to remove the dependency of javassist, So you have to add the jar or Maven dependency the simplest way to find this dependent jar package is to go to the app directory in Struts's full compression package and find the Javassist-3.11.0.ga.jar dependency plus.

Struts Start Error javassist library is missing