Issue
My spring web application is using servlet api 2.5 along with spring framework 4. Its deployed in tomcat 9. Its working fine. I am not sure why tomcat is not complaining about it as it needs servlet api 4 as per documentation. Is it backward compatible or spring is doing some magic? Just for clarity We are using interfaces from servlet api 2.5 in our code which should not compile with servlet api 4. It is compiling because we are compiling with 2.5 but we are expecting it to fail at runtime in tomcat. Thanks
Solution
Are you using methods/classes that no longer exist in servlet spec 4? There isn't magic - it's downward compatible. If you tried to run, for example, AsyncEvent code in Tomcat 5.5 (servlet spec 2.4) then yes, you'd have a problem. But running old code on a new server - without using things that have totally changed or disappeared - is rarely a problem.
EDIT
You said that the "old" code has:
Map parameterMap = request.getParameterMap();
This is still valid if not best practice. With newer compilers you may get a warning from the compiler that you are not using generics but it is still valid. And since the Javadocs from that time say:
Returns: an immutable java.util.Map containing parameter names as keys and parameter values as map values. The keys in the parameter map are of type String. The values in the parameter map are of type String array.
So your old code must be casting the keys as a String and the values as a String[] - just like the newer code that would be:
Map<String, String[]> parameterMap = request.getParameterMap();
Both versions will compile in recent versions of the compiler though, again, you may get warnings with the code that doesn't take advantage of generics.
The key is the use of generics - the <String, String[]> part. It's clearer code when using generics and the compiler can help with issues. With the non-generics version you could have tried to cast the key in the map to any object. It would compile but at runtime you'd likely get a ClassCastException.
From the perspective of Tomcat it's still returning the same thing.
Is that clearer?
Answered By - stdunbar
