How to find servlet API version for glassfish server?

While coding a servlet I found a method that says

Since:
    Servlet 3.1

I guess that if I have the autohint from NetBeans to use it is because I have that Servlet version. But I cannot find a place to confirm that. I'm using glassfish4.1 as container. If I go to mypathtoglassfish4.1\glassfish\modules there I can see javax.servlet-api.jar and inside a manifest that says:

Implementation-Version: 3.1.0

Is that the proper way to check that? I'm especially interested in being able to tell my colleagues "go to that jar and check that property" so I'm sure that my code will run on their server.

As alternative, I found a webpage Oracle GlassFish Server 3.1 Application Development Guide that says: "GlassFish Server supports the Java Servlet Specification version 3.0." but obviously for Glassfish 3.1, and I couldn't find one of those for every glassfish version (not even for mine -4.1 )

Solution

Look at Jakarta EE version history. Servlet (and JSP, JSF, EJB, JPA, etc) version goes hand in hand with Jakarta EE version:

Jakarta EE 10 = Servlet 6.0
Jakarta EE 9 = Servlet 5.0
Jakarta/Java EE 8 = Servlet 4.0
Java EE 7 = Servlet 3.1
Java EE 6 = Servlet 3.0
Java EE 5 = Servlet 2.5
J2EE 1.4 = Servlet 2.4
J2EE 1.3 = Servlet 2.3
J2EE 1.2 = Servlet 2.2

And look at GlassFish version history:

GlassFish 7.x = Jakarta EE 10
GlassFish 6.x = Jakarta EE 9
GlassFish 5.x = Jakarta/Java EE 8
GlassFish 4.x = Java EE 7
GlassFish 3.x = Java EE 6
GlassFish 2.x = Java EE 5 + clustering support
GlassFish 1.x = Java EE 5

So your GlassFish 4.1 is Java EE 7 / Servlet 3.1.

But, with a big but, that's one thing. The second thing is, the webapp's web.xml version also plays a role. Not everyone knows that.

If your webapp's web.xml is declared conform Servlet 3.1 like below,

<?xml version="1.0" encoding="UTF-8"?>
<web-app 
    xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
    version="3.1">

    <!-- Config here. -->
</web-app>

then your webapp will also really run in Servlet 3.1 modus.

However, if it's declared conform Servlet 3.0 like below or even older,

<?xml version="1.0" encoding="UTF-8"?>
<web-app 
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
    version="3.0">

    <!-- Config here. -->
</web-app>

then your webapp will run in Servlet 3.0 compatibility modus, even when deployed to a Servlet 3.1 compatible container! The above influences the ServletContext#getMajorVersion() and getMinorVersion(), so they actually say nothing about the container, but only about the webapp itself.

If your webapp's web.xml contains a <!DOCTYPE>, regardless of the DTD and the version, then it will run in Servlet 2.3 compatibility modus, even when there's a newer XSD declared!

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "java.sun.com/dtd/web-app_2_3.dtd">
<web-app 
    xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
    version="3.1">

    <!-- This is WRONG! The DOCTYPE must be removed! -->
</web-app>