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 :

JDK1.7
Maven 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 :

pom.xml
    <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.

1. 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.

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

References
Maven : Introduction to the Dependency Mechanism

转自：http://www.mkyong.com/java/servlet-api-2-5-jar-jar-not-loaded/

相关：http://stackoverflow.com/questions/1993493/error-servlet-jar-not-loaded-offending-class-javax-servlet-servlet-class

http://yunzhu.iteye.com/blog/1015416

自己的理解：
WEB-INFO/lib中的jar与Tomcat/lib中的service-api.jar冲突了，Tomcat启动后，只会用他自己的jar，所以自己配置的jar要删掉