Jar not loaded warning/error in Google Web Toolkit (GWT) deployment to tomcat

When a Google Web Toolkit (GWT) web application is deployed to Tomcat web server, you may encounter a warning message as follows.

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

No need to worry too much about this warning message.

This raises just because WebappClassLoader has loaded the servlet.jar already.

The gwt-user.jar already contain the content of the servlet.jar file.

Solution

Even though this message can be ignored, this warning message can be avoided just by replacing the gwt-user.jar file with gwt-servlet.jar (which comes with Google Web Toolkit (GWT) download).

Following image shows the content of the gwt-user.jar, and the content of the servlet.jar is highlighted.

gwt-servlet.jar has been created by removing the content of the servlet.jar from the gwt-user.jar, so this change will not have any impact on your project.

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