Considering Oracle's documentation for ServletContext.setInitParameter method, there is the following assertion when describing the exceptions that could be thrown when setInitParameter is invoked:
To test this, I've created a context parameter at DD (Web Deployment Descriptor - which should be initialized when the application is started) .
So I've tried to change the attribute value expecting for an exception (IllegalStateException in such case).
I'd like to know why this exception isn't thrown?
Context parameter defined at DD:
And the servlet's code that tries to change the context parameter through setInitParameter.
you have misinterpreted the documenation. the docs say that the IllegalStateException occurs when the ServletContext has already been initialized. it DOES NOT say that if you try to override the context parameters. setting the parameters and initialization of ServletContext are 2 different things, although when ServletContext is initiazlized(at deployment time) it is given references to context parameters name/value pairs but they ain't the same.
Regarding your second query the doc say that setInitParameter will return false if you try to set a parameter whose value is already set earlier. so in your case the name/value pairs will not be changed by the method call.