Spring MVC framework features and concepts
- 2. 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
- 3. 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.
- 4. 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
- 5. 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
- 6. Dispatcher Servlet Architecture Uses the Front Controller Design Pattern
- 7. Defining The Dispatcher Servlet Defining a Dispatcher Servlet named "spring" that will intercept all urls to this web application
- 8. 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
- 10. 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
- 11. spring-servlet.xml cont. Define a simple view resolver that looks for JSPs that match a given view name in the director /WEB-INF/jsp
- 12. spring-servlet.xml cont. Tell Spring where to automatically detect controllers
- 14. So What's a Controller Look Like?
- 15. Example: Classroom Controller A Controller that gets a class or all the students in the class
- 16. Mark this class as a controller
- 17. Define what default URLs this class should respond to
- 18. 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.
- 19. 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
- 20. 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
- 21. 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.
- 22. 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
- 23. 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
- 24. 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