servlet-api-2.5.jar jar not loaded

Deployed a “war” file on Tomcat, and hits following error messages :

Jul 17, 2014 7:59:55 PM org.apache.catalina.loader.WebappClassLoader validateJarFile
INFO: validateJarFile(D:\apache-tomcat-7.0.53\webapps\hc\WEB-INF\lib\servlet-api-2.5.jar) - jar not loaded. 
See Servlet Spec 3.0, section 10.7.2. Offending class: javax/servlet/Servlet.class

Tools used :

1. JDK1.7
2. Maven 3
3. Tomcat 7

1. Reason

The Tomcat’s container comes with own version of servlet-api.jar, and the “war” file is deploy the same jar again, and causing the Offending class: javax/servlet/Servlet.class.

This is a really common problem for developers who are using Maven as a build tool. Normally, we will include the servlet-api as a project dependency like this :

	<dependency>
		<groupId>javax.servlet</groupId>
		<artifactId>servlet-api</artifactId>
		<version>2.5</version>
	</dependency>

When building a war file, Maven will include the servlet-api as well.

2. Solution

To fix it, set the scope to provided. This tells Maven use code servlet-api.jar for compiling and testing only, but NOT include it in the WAR file. The deployed container will “provide” the servlet-api.jar at runtime.

	<dependency>
		<groupId>javax.servlet</groupId>
		<artifactId>servlet-api</artifactId>
		<version>2.5</version>
		<scope>provided</scope>
	</dependency>

References

1. Maven : Introduction to the Dependency Mechanism