[Tomcat] validateJarFile(servlet-api.jar) - jar not loaded. Offending class: javax/servlet/Servlet.class

org.apache.catalina.loader.WebappClassLoader validateJarFile
INFO: validateJarFile(<APP_PATH>\WEB-INF\lib\servlet-api.jar) - jar not loaded. See Servlet Spec 2.3, section 9.7.2. Offending class: javax/servlet/Servlet.class.

We are using Apache Tomcat to deploy web applications, and getting the above message when Apache Tomcat is started. All web applications inside Tomcat are working fine, however no developer would want to see this type of messages (at least we do not want to see).

The above message is only a warning message due to the existence of multiples of the same javax.servler.Servlet.class for Tomcat runtime to pick; and this extra instance has come from a jar file at <APP_PATH>\WEB-INF\lib\servlet-api.jar. Tomcat has its own servlet-api.jar file; look at the following folders to locate the file (depending on the Tomcat version; location may be different).

<TOMCAT_HOME>\common\lib
<TOMCAT_HOME>\lib

Your web applications have the same servlet-api.jar file inside following folder.

<TOMCAT_HOME>\webapps\<PROJECT>\WEB-INF\lib

As the Tomcat runtime has the required javax/servlet/Servlet.class file loaded from its own lib\servlet-api.jar file, you do not need to place it inside each and every web application. After removing the jar file from your web application, you will not receive the message again.

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