Q:

How do I know what version of servlet-api.jar I have?

I downloaded a copy of servlet-api.jar from java2s.com.  How do I know what version it is?  There's no reference on the site.
EDIT
Ah.  Apologies.  I should have listed the content of the wordpad output when I double clicked on the MANIFEST.MF file in the jar I got:
Manifest-Version: 1.0
Ant-Version: Apache Ant 1.6.5
Created-By: 1.5.0_06-b05 (Sun Microsystems Inc.)

As you can see it didnt tell me the version hence the question.

A:

you can get it from META-INF, you can explore the content of jar file using win rar or such archiving utils  something like.
Name: javax/servlet/
Specification-Title: Java API for Servlets
Specification-Version: 2.4  

I personally prefer maven repo to download jar from.

A:

use the below code snippet : 
<%= session.getServletContext().getMajorVersion() %>.
<%= session.getServletContext().getMinorVersion() %>

A:

you can extract the MANIFEST.MF from the META-INF directory of your jar file by using
jar xf servlet-api.jar META-INF/MANIFEST.MF

the manifest for version 2.4 that comes with tomcat looks like this for example
Manifest-Version: 1.0
Ant-Version: Apache Ant 1.6.2
Created-By: 1.4.2_06-b03 (Sun Microsystems Inc.)

Name: javax/servlet/
Specification-Title: Java API for Servlets
Specification-Version: 2.4
Specification-Vendor: Sun Microsystems, Inc.
Implementation-Title: javax.servlet
Implementation-Version: 2.4.public_draft
Implementation-Vendor: Apache Software Foundation

