Spring having much of demand because of the following 3 reasons as-
1 Simplicity-Spring framework is simple because as it is non-invasive,
POJO and POJI model.
2 Testability-Writing the spring application, server [Container] is
not mandatory, spring has it own container to run the applications.
3 Loose Coupling-In spring objects are loosely coupled, this is the
core concept of spring framework.