Spring MVC framework features and concepts

What's Spring MVC?
A model-view-controller framework for Java
web application
Made to simplify the writing and testing of
Java web applications
Fully integrates with the Spring dependency
injection (Inversion of Control) framework
Open Source
Developed and maintained by Interface21,
recently purchased by VMWare

Project Goals
J2EE should be easier to use
It is best to program to interfaces, rather than
classes. Spring reduces the complexity cost of using
interfaces to zero.
JavaBeans offer a great way of configuring
applications.
OO design is more important than any
implementation technology, such as J2EE.
Checked exceptions are overused in Java. A platform
shouldn't force you to catch exceptions you're
unlikely to be able to recover from.
Testability is essential, and a platform such as Spring
should help make your code easier to test.

Why Use Spring MVC?
• For most purposes you only have to define one
Servlet in web.xml
• Capable of Convention over Configuration Similar
to Ruby on Rails or other popular web frameworks
that work with dynamic languages
• Normal business objects can be used to back forms No
need to duplicate objects just to implement an MVC's
command object interface
• Very flexible view resolvers
• Can by used to map *.json, *.xml, *.atom, etc to the
same logic code in one controller and simply output
the type of data requested
• Enforces good Software Engineering principles like
SRP and DRY

Dispatcher Servlet
Used to handle all incoming requests and route
them through Spring
Uses customizable logic to determine which
controllers should handle which requests
Forwards all responses to through view handlers
to determine the correct views to route responses
to
Exposes all beans defined in Spring to controllers
for dependency injection

Dispatcher Servlet Architecture
Uses the Front Controller Design Pattern

Defining The Dispatcher Servlet
Defining a Dispatcher Servlet named "spring" that will intercept all
urls to this web application

Spring Configuration
By default Spring looks for a servletname -
servlet.xml file in /WEB-INF
For the previous example we would need to
create a file in /WEB-INF named spring-servlet.
xml

spring-servlet.xml cont.
<mvc:annotation-driven /> tells Spring to support annotations like
@Controller, @RequestMapping and others that simplify the
writing and configuration of controllers

Define a simple view resolver that looks for JSPs that match a given
view name in the director /WEB-INF/jsp

Tell Spring where to automatically detect controllers

So What's a Controller Look Like?

Example: Classroom Controller
A Controller that gets a class or all the students in the class

Mark this class as a controller

Define what default URLs this class should respond to

Side Note: Autowiring
Autowiring allows Spring to do the instantiation of the class you
want to make use of for you. At run time you will be able to access
all methods of the class without worrying about how you got the
class. This is known as Dependency Injection.

Back To Classroom Example
This method is the default method called when /classroom or / is
hit from a client. It simply forwards to a jsp named classroom.jsp
located in /WEB-INF/jsp

Side Note: Restful URLs
• Spring like many other popular frameworks can make use
of RESTful URLs
• They come in the style of /users/user_id
• Commonly without any extension such as .html
• Popularized by Ruby on Rails
• Collections are accessed like:
• /users
• Individual entries are accessed like:
• /users/user_id
• CRUD operations are done via HTTP
methods PUT, POST, GET, DELETE

Classroom RESTful URLs
The highlighted section above demonstrates how to accomplish
RESTful URLs in the Spring MVC Framework. Using the
@PathVariable annotation you can gain access to the variable
passed in on the URI. This is commonly referred to as URI
Templating.

What's a Model?
• A Model is used in Spring MVC to pass
objects from the controller tier up into the view.
• A Model is really just a java.util.Map
• You can add attributes to a Model and they
will be put on the request as attributes and
available in the applications PageContext .
• In Spring you can simply pass back a Map or
one of two Spring specific classes; ModelMap or
Model

ModelMap Example
In the above example we use a service method to read and return
a Classroom object. We make that Classroom object available to
the view under the key "classroom " by calling addAttribute() on
the ModelMap

Getting All Students In A Classroom
Above you can see that how to get all the students in a given
classroom by requesting the URL /classroom/{id} /students. A
Java List<Student> will be available to the classroom.jsp view for
display

Spring MVC framework features and concepts

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