YourNote 701: MVC Pattern in JEE

MVC Pattern in JEE (Java Enterprise Edition)

MVC (Model-View-Controller) is a design pattern used in JEE web applications where Servlets act as Controllers, JSP pages act as Views, and JavaBeans/DAO classes act as Models, providing a clear separation between presentation, business logic, and data access.

1. MVC Components

A. Model

The Model contains:

• Business logic
• Data processing
• Database access (JDBC, JPA, Hibernate)
• JavaBeans

Example:

public class Student {
    private String matricNo;
    private String name;

    // Getter and Setter
}

or

public class StudentDAO {

    public Student getStudent(String matricNo) {
        // Retrieve data from database
    }
}

B. View

The View is responsible for:

• User Interface
• Displaying data
• Receiving user input

In JEE, View is usually:

• JSP
• HTML
• CSS
• JavaScript

Example:

<h2>Student Information</h2>
<p>Name: ${student.name}</p>
<p>Matric No: ${student.matricNo}</p>

The View should NOT contain database code.

C. Controller

The Controller acts as the middleman.

Responsibilities:

• Receive user requests
• Validate input
• Call Model
• Send data to View

In JEE, Controller is usually a Servlet.

Example:

@WebServlet("/student")
public class StudentServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request,
                         HttpServletResponse response)
                         throws ServletException, IOException {

        StudentDAO dao = new StudentDAO();

        Student student = dao.getStudent("A123");

        request.setAttribute("student", student);

        RequestDispatcher rd =
            request.getRequestDispatcher("student.jsp");

        rd.forward(request, response);
    }
}

2. MVC Flow in JEE

Browser
   |
   | Request
   v
Servlet (Controller)
   |
   | Calls
   v
Model (JavaBean/DAO)
   |
   | Returns Data
   v
Servlet (Controller)
   |
   | Forward
   v
JSP (View)
   |
   | Response
   v
Browser

Step-by-Step

1. User opens:

http://localhost:8080/login.jsp

2. Request goes to Servlet.
3. Servlet calls DAO.
4. DAO retrieves data from MySQL.
5. DAO returns data to Servlet.
6. Servlet stores data:

request.setAttribute("student", student);

7. Servlet forwards to JSP.
8. JSP displays the data.
9. Browser shows the result.

3. MVC Project Structure

StudentMVC
│
├── src
│   └── my/zhamri
│       ├── Student.java
│       ├── StudentDAO.java
│       └── StudentServlet.java
│
├── webapp
│   ├── student.jsp
│   └── index.jsp
│
└── WEB-INF

4. Advantages of MVC

Advantage	Description
Separation of Concerns	Each component has a specific responsibility
Easier Maintenance	Changes can be made independently
Reusability	Model can be reused by different views
Better Testing	Components can be tested separately
Team Development	Frontend and backend can work independently

5. Bad Practice (No MVC)

<%
Connection con =
DriverManager.getConnection(...);

Statement stmt =
con.createStatement();

ResultSet rs =
stmt.executeQuery("SELECT * FROM student");
%>

Problems:

• SQL inside JSP
• Difficult to maintain
• Difficult to debug
• Poor scalability