web.xml中与Servlet 3.0兼容的web-app声明有什么作用？

Question

I am deploying a web application that is declared in web.xml and deployed as a .war file.

I am deploying on Jetty 9.1.x (but I think this question is not container specific).

My web.xml file is quite old and declares itself as a Servlet 2.4 application:

<web-app version="2.4" id="my_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/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">

My configuration actually declares some Servlet 3.0 only features, like a default error page. These features do not validate according to the schema, but the features seem to work correctly.

Since I am using 3.0 features, I would like to change the declaration to be correct:

<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">

But I am scared to do this because I don't understand what the difference will be to Jetty.

Will changing the declaration have any effect on the runtime behavior of Jetty? Does Jetty treat a 2.4 app somehow differently than a 3.0 app?

Answer 1

You should be able to simply swap the schema declaration from 2.4 to 3.0 .

Scientific method

Initially I set off to prove it by doing diff between 2.4 and 2.5 and another one comparing 2.5 and 3.0 .

I have convinced myself that the differences between 2.4 and 2.5 are only additive and the name space have shifted from j2ee to javaee .

However xsd schema for 3.0 is smaller then 1/3rd of the other two versions. Not sure how to proceed in this case (any ideas welcome!)

You can download all schemas from here and do the comparison yourself:

• web xml v2.4 xsd schema
• web.xml v2.5 xsd schema
• web.xml v3.0 xsd schema

Not so scientific method

Here are the what's new articles describing each new version of the standard:

• What's new in Servlet 2.4
• What's new in Servlet 2.5
• What's new in Servlet 3.0

If you read in, the changes to web.xml descriptor mentioned in the articles are minute.

What I would do is simply list all the elements in your original web.xml and confirm that they do exist in this document describing the 3.0 schema .

Hope this helps!