The Spring framework has its own MVC Web application
framework, which was not originally intended. The developers of Spring decided
to write their own web framework as a reaction to what they perceived as the
bad design of the (then) popular Jakarta Struts Web framework, Other frames
available. In particular, they found that there was insufficient separation
between the presentation and request processing layers and between the
application processing layer and the model
Like Struts, Spring MVC is a query-based framework. The
framework defines the policy interfaces for all responsibilities that must be
addressed by a modern demand-driven framework. The goal of each interface is to
be simple and clear so that it is easy for Spring MVC users to write their own
implementations if they wish. MVC paves the way for a cleaner front end code.
All interfaces are tightly coupled to the Servlet API. This tight coupling to
the Servlet API is perceived by some as a failure on the part of Spring's
developers to provide high-level abstraction for Web applications [citation
needed]. However, this coupling ensures that the functionality of the Servlet
API remains available to developers while providing a high abstraction
framework to facilitate work with said API.
The DispatcherServlet class is the front-end controller [20]
of the framework and is responsible for delegating control to the different
interfaces during the execution phases of an HTTP request.
The most important interfaces defined by Spring MVC and
their responsibilities are listed below:
Controller: Between Model and View to handle incoming
requests and redirect to the correct answer. It acts as a gateway that directs
incoming information. It switches between the entry in the model or the view.
HandlerAdapter: Running objects that handle incoming
requests
HandlerInterceptor: Incoming query interception comparable
but not equal to Servlet filters (use is optional and not controlled by
DispatcherServlet).
HandlerMapping: selection of objects that handle incoming
requests (managers) according to any attribute or condition internal or
external to these requests
LocaleResolver: resolution and optionally saving the locale
of an individual user
MultipartResolver: makes it easy to work with file downloads
by wrapping incoming requests
View: Responsible for returning a response to the client.
Some requests can go directly to the view without going to the template part;
Others can go through all three.
ViewResolver: Select a view based on a logical name for the
view (use is not strictly required)
Each strategy interface above has an important
responsibility within the overall framework. The abstractions offered by these
interfaces are powerful, to allow a set of variations in their implementations,
Spring MVC embeds with implementations of all these interfaces and together
offers a set of features on top of the Servlet API. However, developers and
vendors are free to write other implementations. Spring MVC uses the Java
interface java.util.Map as a data-oriented abstraction for the model where the
keys are supposed to be string values.
The ease of testing the implementations of these interfaces
seems to be an important advantage of the high level of abstraction offered by
Spring MVC. DispatcherServlet is tightly coupled to the control container's
spring inversion to configure application web layers. However, Web applications
can use other parts of the Spring Framework, including the container, and
choose not to use Spring MVC.
