Model View Controller - MVC

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Integrating Servlets and JSP

Concepts

• Understanding the benefits of MVC
• Using RequestDispatcher to implement MVC
• Forwarding requests from servlet to JSP pages

Understanding the Need for MVC

    Simple application or       * Call Java code directly.
    small development team.     * Call Java code indirectly.
                |               * Use JavaBeans.
                |               * Use the MVC architecture.
                |               * Use the JSP expression language.
                v               * Use JSP 2.0 and JSTL.
    Complex application or      * Use Custom tags.
    large development team.     * Use a web development framework.

• Servlets are great for handling HTTP Requests and for general Java coding.
• Business logic really belongs in Java classes that don’t know anything about HTTP.
• JSP is really good at presentation of information.
• The best approach is to use all three! We let each part do what it is best at.
• The formal name for this approach is the Model View Controller (MVC) architecture.

MVC Overview in Web Applications

Implementing MVC

1. Define JavaBeans to represent the data.
2. Use a servlet to handle HTTP Requests.
3. Populate the JavaBeans using business classes.
4. Store the JavaBeans in the request, session, or servlet context.
5. Forward or Redirect the request to a JSP page.
6. Extract the data from the JavaBeans on the JSP pages.

JavaBeans? What are JavaBeans?

• JavaBeans are just plain, old, Java classes (POJOs) that follow a few rules.
• A JavaBean must have a zero-argument constructor.
• A JavaBean should have only private instance variables.

• A JavaBean should have proper get and set methods for its instance variables.

  • For non-boolean variables you should have get and set methods:

    private String name;
    
    public String getName() {
        return name;
    }
    
    public void setName(String name) {
        this.name = name;
    }
    

  • For boolean variables you should have a set method and an “is” method:

    private boolean connected;
    
    public boolean isConnected() {
        return connected;
    }
    
    public void setConnected(boolean connected) {
        this.connected = connected;
    }
    

• Example: BeanOne.java

Using JavaBeans in JSP

• When using JavaBeans on a JSP page we’ll use the EL.

• A servlet could create a bean and put it in the session.

  public void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
  
      BeanOne bean = new BeanOne();
  
      request.setAttribute("myCoolBean", bean);
  
      String url = "/beanOneDemo.jsp";
  
      RequestDispatcher  dispatcher =
              getServletContext().getRequestDispatcher(url);
      dispatcher.forward(request, response);
  
  }
  

• Then we access the data property like this example:

  • ${myCoolBean.data}