Spring MVC

Note

• To be continued

Spring MVC Framework is a Java-based web framework built on the Model-View-Controller design pattern. It is part of the Spring Framework and is used to develop flexible and loosely coupled web applications.

• It uses DispatcherServlet as the front controller to handle all incoming requests and route them to appropriate controllers.
• It separates application logic into Model (data), View (UI), and Controller (request handling) for better organization.
• It supports features like form handling, validation, and RESTful web services for building modern web applications.

DispatcherServlet

Servlet (Old way)

• A Servlet is a Java-based server-side class used to handle requests and generate dynamic responses for web applications

• The servlet must be run on the servlet container (e.g., Apache Tomcat) instead of directly on JVM

• External or embedded server

• Servlet lifecycle

  1. Loading and initialisation

     • When a servlet is requested for the first time or after a container restart, the servlet container loads the servlet class into memory

     • The container calls the init() method, which is used to initialize the servlet

     • init() is called only once during the servlet’s lifecycle and is used to perform any initializations required for the servlet

  2. Request handling

     • service() method is called for each request made to the servlet

     • It is responsible for processing the client request and generating the response

     • The container calls service() whenever it receives an HTTP request (usually via doGet(), doPost(), etc.)

     • In the case of HttpServlet, the service() method delegates the request to specific methods based on the HTTP method (GET, POST, etc.):

       • doGet(): Handles HTTP GET requests (commonly used for retrieving data from the server).
       • doPost(): Handles HTTP POST requests (commonly used for submitting data to the server).
       • doPut(), doDelete(): Handle PUT and DELETE requests, respectively.
       • doHead(), doOptions(): Handle other HTTP request types like HEAD and OPTIONS.

  3. Destroying the servlet

     • When the servlet container decides to unload the servlet (typically when the server shuts down or the servlet is no longer needed), it calls the destroy() method

     • This is where cleanup tasks such as releasing resources (like database connections or file handles) should be done

• How to create a servlet?

  1. Extend HttpServlet
  2. Override doGet(), doPOst(), etc.
  3. Configure using web.xml or WebServlet annotation

• import java.io.IOException;
  import javax.servlet.ServletException;
  import javax.servlet.annotation.WebServlet;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  // Annotation-based servlet mapping
  @WebServlet("/hello")
  public class HelloServlet extends HttpServlet {
  
      @Override
      public void init() throws ServletException {
          System.out.println("Servlet Initialized");
      }
  
    	@Override
      protected void doGet(HttpServletRequest request, HttpServletResponse response)
              throws ServletException, IOException {
          response.setContentType("text/html");
          response.getWriter().println("<h1>Hello, Servlet!</h1>");
      }
  
    	@Override
    	protected void doPost(HttpServletRequest request, HttpServletResponse response)
        			throws ServletException, IOException {
          // Handle POST request
          String data = request.getParameter("data");
          response.getWriter().write("Received POST data: " + data);
  		}
  
    	@Override
      public void destroy() {
          System.out.println("Servlet Destroyed");
      }
  }