THe XSD doesn't have to be on the internet for spring to work. The XSD can be inside a JAR file in the classpath. That JAR file needs to have a spring.schemas file that maps the URL to the XSD inside the JAR file THis document
describes how Spring namespaces are handled
Generally, if you get an error from Spring that says that it can;t locate the namespace XSD, the problem is that you have a JAR file missing in your classpath (or you have merely misspelled something in the namespace declaration)
1) DOuble check your name space declaration. There might be silly mistake
2) Look at your dependencies. You probably have a jar file missing. THis could happen if you have the wrong version of spring web flow.
Ok my hunch was correct. I looked at your POM, and it has
So, you are using 2.3.3 release of spring web flow, but referring to 2.4.xsd. That's not going to work. You need to have the correct version.