we have 2 applications (Say AppA and AppB) that use Struts 1.3.
I want to upgrade AppB to use struts 2.3, however I cannot make changes to AppA so it will have to remain in Struts 1.3.
The problem is that AppB has some dependencies on AppA such as extending Actions classes, tag classes, filters, etc..
Is Struts backward compatible?
Not exactly. However, you can have both libraries running and responding to separate paths. Do this in your web.xml servlet mapping. For example: /struts1/*.do and /*.do
Unfortunately, this will not allow you to extend Actions from struts1 in struts 2. (You probably wouldn't want to, anyway.)
You can add a plugin to Struts2 apps to run Struts1 Actions. This might be the fastest way to get your situation working. More information here: https://struts.apache.org/docs/struts-1-plugin.html
Assuming you can't change AppA, the next best option is to just create new Struts2 base classes in AppB. Hopefully, you can crib liberally from AppA.