Java Notes

MVC Architecture

Complete guide to Model-View-Controller (MVC) pattern in Java web applications - implementing MVC with Servlets and JSP, Front Controller pattern, and practical examples.

What is MVC?

MVC (Model-View-Controller) is a design pattern that separates an application into three interconnected components:

Model — Data and business logic (JavaBeans, POJOs, Services)
View — Presentation layer (JSP pages, HTML templates)
Controller — Handles requests, coordinates Model and View (Servlets)

Why MVC?

Without MVC	With MVC
HTML mixed with Java logic	Clean separation
Hard to test	Easy unit testing
One developer does everything	Team can work in parallel
Changes break other parts	Changes isolated to one layer
Code duplication	Reusable components

Implementing MVC: Student Management Example

Model Layer

Student.java (JavaBean/POJO)

java example

package com.example.model;

public class Student {
    private int id;
    private String name;
    private String email;
    private int age;
    private String course;

    public Student() {}

    public Student(int id, String name, String email, int age, String course) {
        this.id = id;
        this.name = name;
        this.email = email;
        this.age = age;
        this.course = course;
    }

    // Getters and Setters
    public int getId() { return id; }
    public void setId(int id) { this.id = id; }
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public String getEmail() { return email; }
    public void setEmail(String email) { this.email = email; }
    public int getAge() { return age; }
    public void setAge(int age) { this.age = age; }
    public String getCourse() { return course; }
    public void setCourse(String course) { this.course = course; }
}

StudentDAO.java (Data Access Object)

java example

package com.example.dao;

import com.example.model.Student;
import java.sql.*;
import java.util.*;

public class StudentDAO {
    private Connection connection;

    public StudentDAO(Connection connection) {
        this.connection = connection;
    }

    public List<Student> getAllStudents() throws SQLException {
        List<Student> students = new ArrayList<>();
        String sql = "SELECT * FROM students ORDER BY id";
        
        try (PreparedStatement ps = connection.prepareStatement(sql);
             ResultSet rs = ps.executeQuery()) {
            while (rs.next()) {
                students.add(mapRow(rs));
            }
        }
        return students;
    }

    public Student getById(int id) throws SQLException {
        String sql = "SELECT * FROM students WHERE id = ?";
        try (PreparedStatement ps = connection.prepareStatement(sql)) {
            ps.setInt(1, id);
            try (ResultSet rs = ps.executeQuery()) {
                if (rs.next()) return mapRow(rs);
            }
        }
        return null;
    }

    public void insert(Student student) throws SQLException {
        String sql = "INSERT INTO students (name, email, age, course) VALUES (?, ?, ?, ?)";
        try (PreparedStatement ps = connection.prepareStatement(sql)) {
            ps.setString(1, student.getName());
            ps.setString(2, student.getEmail());
            ps.setInt(3, student.getAge());
            ps.setString(4, student.getCourse());
            ps.executeUpdate();
        }
    }

    public void update(Student student) throws SQLException {
        String sql = "UPDATE students SET name=?, email=?, age=?, course=? WHERE id=?";
        try (PreparedStatement ps = connection.prepareStatement(sql)) {
            ps.setString(1, student.getName());
            ps.setString(2, student.getEmail());
            ps.setInt(3, student.getAge());
            ps.setString(4, student.getCourse());
            ps.setInt(5, student.getId());
            ps.executeUpdate();
        }
    }

    public void delete(int id) throws SQLException {
        String sql = "DELETE FROM students WHERE id = ?";
        try (PreparedStatement ps = connection.prepareStatement(sql)) {
            ps.setInt(1, id);
            ps.executeUpdate();
        }
    }

    private Student mapRow(ResultSet rs) throws SQLException {
        return new Student(
            rs.getInt("id"),
            rs.getString("name"),
            rs.getString("email"),
            rs.getInt("age"),
            rs.getString("course")
        );
    }
}

StudentService.java (Business Logic)

Example

package com.example.service; import com.example.dao.StudentDAO; import com.example.model.Student; import java.util.*; public class StudentService { private StudentDAO studentDAO; public StudentService(StudentDAO studentDAO) { this.studentDAO = studentDAO; } public List<Student> getAllStudents() { try { return studentDAO.getAllStudents(); } catch (Exception e) { throw new RuntimeException("Failed to fetch students", e); } } public Student getStudent(int id) { try { Student student = studentDAO.getById(id); if (student == null) throw new RuntimeException("Student not found: " + id); return student; } catch (Exception e) { throw new RuntimeException("Failed to fetch student", e); } } public void addStudent(Student student) { // Business validation if (student.getName() == null || student.getName().trim().isEmpty()) { throw new IllegalArgumentException("Name is required"); } if (student.getAge() < 16 || student.getAge() > 60) { throw new IllegalArgumentException("Age must be between 16 and 60"); } try { studentDAO.insert(student); } catch (Exception e) { throw new RuntimeException("Failed to add student", e); } } }

Controller Layer

StudentController.java (Servlet)

Example

package com.example.controller; import com.example.model.Student; import com.example.service.StudentService; import jakarta.servlet.*; import jakarta.servlet.http.*; import jakarta.servlet.annotation.*; import java.io.*; import java.util.*; @WebServlet("/students/*") public class StudentController extends HttpServlet { private StudentService studentService; @Override public void init() throws ServletException { // Initialize service (in real app, use dependency injection) studentService = new StudentService(new StudentDAO(getDBConnection())); } @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String action = request.getPathInfo(); if (action == null) action = "/list"; switch (action) { case "/list": listStudents(request, response); break; case "/add": showAddForm(request, response); break; case "/edit": showEditForm(request, response); break; case "/delete": deleteStudent(request, response); break; default: listStudents(request, response); } } @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String action = request.getPathInfo(); switch (action) { case "/add": addStudent(request, response); break; case "/edit": updateStudent(request, response); break; default: response.sendRedirect(request.getContextPath() + "/students/list"); } } private void listStudents(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { List<Student> students = studentService.getAllStudents(); request.setAttribute("students", students); request.setAttribute("totalCount", students.size()); forward(request, response, "/WEB-INF/views/student-list.jsp"); } private void showAddForm(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { forward(request, response, "/WEB-INF/views/student-form.jsp"); } private void addStudent(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { try { Student student = new Student(); student.setName(request.getParameter("name")); student.setEmail(request.getParameter("email")); student.setAge(Integer.parseInt(request.getParameter("age"))); student.setCourse(request.getParameter("course")); studentService.addStudent(student); request.getSession().setAttribute("message", "Student added successfully!"); response.sendRedirect(request.getContextPath() + "/students/list"); } catch (Exception e) { request.setAttribute("error", e.getMessage()); forward(request, response, "/WEB-INF/views/student-form.jsp"); } } private void forward(HttpServletRequest request, HttpServletResponse response, String path) throws ServletException, IOException { RequestDispatcher dispatcher = request.getRequestDispatcher(path); dispatcher.forward(request, response); } }

View Layer

student-list.jsp

jsp example

<%@ page contentType="text/html;charset=UTF-8" %>
<%@ taglib uri="jakarta.tags.core" prefix="c" %>

<!DOCTYPE html>
<html>
<head><title>Student Management</title></head>
<body>
    <h2>Students (${totalCount})</h2>
    
    <c:if test="${not empty sessionScope.message}">
        <p style="color:green">${sessionScope.message}</p>
        <c:remove var="message" scope="session" />
    </c:if>
    
    <a href="${pageContext.request.contextPath}/students/add">Add New Student</a>
    
    <table border="1">
        <tr>
            <th>ID</th><th>Name</th><th>Email</th>
            <th>Age</th><th>Course</th><th>Actions</th>
        </tr>
        <c:forEach var="student" items="${students}">
            <tr>
                <td>${student.id}</td>
                <td>${student.name}</td>
                <td>${student.email}</td>
                <td>${student.age}</td>
                <td>${student.course}</td>
                <td>
                    <a href="${pageContext.request.contextPath}/students/edit?id=${student.id}">Edit</a>
                    <a href="${pageContext.request.contextPath}/students/delete?id=${student.id}"
                       onclick="return confirm('Delete this student?')">Delete</a>
                </td>
            </tr>
        </c:forEach>
    </table>
</body>
</html>

student-form.jsp

jsp example

<%@ page contentType="text/html;charset=UTF-8" %>
<%@ taglib uri="jakarta.tags.core" prefix="c" %>

<!DOCTYPE html>
<html>
<head><title>${empty student ? "Add" : "Edit"} Student</title></head>
<body>
    <h2>${empty student ? "Add New" : "Edit"} Student</h2>
    
    <c:if test="${not empty error}">
        <p style="color:red">${error}</p>
    </c:if>
    
    <form method="POST" action="${pageContext.request.contextPath}/students/${empty student ? 'add' : 'edit'}">
        <c:if test="${not empty student}">
            <input type="hidden" name="id" value="${student.id}" />
        </c:if>
        
        <label>Name:</label><br>
        <input type="text" name="name" value="${student.name}" required /><br><br>
        
        <label>Email:</label><br>
        <input type="email" name="email" value="${student.email}" required /><br><br>
        
        <label>Age:</label><br>
        <input type="number" name="age" value="${student.age}" min="16" max="60" required /><br><br>
        
        <label>Course:</label><br>
        <select name="course">
            <option value="Java" ${student.course == 'Java' ? 'selected' : ''}>Java</option>
            <option value="Python" ${student.course == 'Python' ? 'selected' : ''}>Python</option>
            <option value="Web Development" ${student.course == 'Web Development' ? 'selected' : ''}>Web Development</option>
        </select><br><br>
        
        <button type="submit">Save</button>
        <a href="${pageContext.request.contextPath}/students/list">Cancel</a>
    </form>
</body>
</html>

Front Controller Pattern

A Front Controller is a single servlet that handles ALL requests and dispatches to appropriate handlers:

java example

@WebServlet("/app/*")
public class FrontController extends HttpServlet {

    private Map<String, RequestHandler> handlers = new HashMap<>();

    @Override
    public void init() {
        handlers.put("/students", new StudentHandler());
        handlers.put("/courses", new CourseHandler());
        handlers.put("/reports", new ReportHandler());
    }

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        
        String path = request.getPathInfo();
        RequestHandler handler = findHandler(path);
        
        if (handler != null) {
            handler.handle(request, response);
        } else {
            response.sendError(404);
        }
    }
}

This is essentially what Spring MVC's DispatcherServlet does!

Project Structure (MVC)

src/ ├── main/ │ ├── java/ │ │ └── com/example/ │ │ ├── controller/ ← Servlets │ │ │ ├── StudentController.java │ │ │ └── CourseController.java │ │ ├── model/ ← POJOs/Beans │ │ │ ├── Student.java │ │ │ └── Course.java │ │ ├── dao/ ← Database access │ │ │ ├── StudentDAO.java │ │ │ └── CourseDAO.java │ │ ├── service/ ← Business logic │ │ │ ├── StudentService.java │ │ │ └── CourseService.java │ │ └── filter/ ← Filters │ │ └── AuthFilter.java │ └── webapp/ │ ├── WEB-INF/ │ │ ├── views/ ← JSP pages (not directly accessible) │ │ │ ├── student-list.jsp │ │ │ ├── student-form.jsp │ │ │ └── error.jsp │ │ └── web.xml │ ├── css/ │ ├── js/ │ └── index.html

MVC Benefits Summary

Benefit	Explanation
Separation of Concerns	Each layer has one job
Testability	Model and Service tested independently
Parallel Development	Frontend/Backend developers work separately
Reusability	Models reused across different views
Maintainability	Change view without touching logic
Scalability	Easy to add new features

Interview Key Points

MVC separates data (Model), UI (View), and logic (Controller)
In Java web apps: Model=JavaBeans, View=JSP, Controller=Servlet
Controller receives request, calls Model, forwards to View
JSP pages should NEVER be directly accessible (put in WEB-INF)
Front Controller pattern = single entry point for all requests
Spring MVC is a sophisticated implementation of this pattern
DAO pattern separates database logic from business logic

Summary

In this chapter, we learned about MVC Architecture in detail. Here are the key points:

Basic introduction to the concept and why it is needed
Syntax and structure with complete examples
Internal working and best practices
Real-world applications and use cases
Common mistakes and how to avoid them
How this topic is asked in interviews

To practice these concepts, write and run the code in your IDE and verify the output. Modify each example and experiment so that you deeply understand the concept.

Key Takeaways for Mvc Architecture

This topic is fundamental in Java development and is frequently asked in interviews
Make sure to do hands-on practice for practical implementation
Understanding its use in real-world projects is important for writing production-ready code
Keep referring to documentation and official Java docs for the latest updates
Also develop testing and debugging skills alongside this topic
Follow industry best practices and actively participate in code reviews

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for MVC Architecture.

Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this Java Master Course topic.

Search Terms

java-master-course, java master course, java, master, course, servlets, jsp, mvc

Continue learning this concept

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PreviousJSP Tags and JSTL NextRequest and Response Objects

Java Notes

MVC Architecture

Complete guide to Model-View-Controller (MVC) pattern in Java web applications - implementing MVC with Servlets and JSP, Front Controller pattern, and practical examples.

What is MVC?

MVC (Model-View-Controller) is a design pattern that separates an application into three interconnected components:

Model — Data and business logic (JavaBeans, POJOs, Services)
View — Presentation layer (JSP pages, HTML templates)
Controller — Handles requests, coordinates Model and View (Servlets)

Why MVC?

Without MVC	With MVC
HTML mixed with Java logic	Clean separation
Hard to test	Easy unit testing
One developer does everything	Team can work in parallel
Changes break other parts	Changes isolated to one layer
Code duplication	Reusable components

Implementing MVC: Student Management Example

Model Layer

Student.java (JavaBean/POJO)

java example

package com.example.model;

public class Student {
    private int id;
    private String name;
    private String email;
    private int age;
    private String course;

    public Student() {}

    public Student(int id, String name, String email, int age, String course) {
        this.id = id;
        this.name = name;
        this.email = email;
        this.age = age;
        this.course = course;
    }

    // Getters and Setters
    public int getId() { return id; }
    public void setId(int id) { this.id = id; }
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public String getEmail() { return email; }
    public void setEmail(String email) { this.email = email; }
    public int getAge() { return age; }
    public void setAge(int age) { this.age = age; }
    public String getCourse() { return course; }
    public void setCourse(String course) { this.course = course; }
}

StudentDAO.java (Data Access Object)

java example

package com.example.dao;

import com.example.model.Student;
import java.sql.*;
import java.util.*;

public class StudentDAO {
    private Connection connection;

    public StudentDAO(Connection connection) {
        this.connection = connection;
    }

    public List<Student> getAllStudents() throws SQLException {
        List<Student> students = new ArrayList<>();
        String sql = "SELECT * FROM students ORDER BY id";
        
        try (PreparedStatement ps = connection.prepareStatement(sql);
             ResultSet rs = ps.executeQuery()) {
            while (rs.next()) {
                students.add(mapRow(rs));
            }
        }
        return students;
    }

    public Student getById(int id) throws SQLException {
        String sql = "SELECT * FROM students WHERE id = ?";
        try (PreparedStatement ps = connection.prepareStatement(sql)) {
            ps.setInt(1, id);
            try (ResultSet rs = ps.executeQuery()) {
                if (rs.next()) return mapRow(rs);
            }
        }
        return null;
    }

    public void insert(Student student) throws SQLException {
        String sql = "INSERT INTO students (name, email, age, course) VALUES (?, ?, ?, ?)";
        try (PreparedStatement ps = connection.prepareStatement(sql)) {
            ps.setString(1, student.getName());
            ps.setString(2, student.getEmail());
            ps.setInt(3, student.getAge());
            ps.setString(4, student.getCourse());
            ps.executeUpdate();
        }
    }

    public void update(Student student) throws SQLException {
        String sql = "UPDATE students SET name=?, email=?, age=?, course=? WHERE id=?";
        try (PreparedStatement ps = connection.prepareStatement(sql)) {
            ps.setString(1, student.getName());
            ps.setString(2, student.getEmail());
            ps.setInt(3, student.getAge());
            ps.setString(4, student.getCourse());
            ps.setInt(5, student.getId());
            ps.executeUpdate();
        }
    }

    public void delete(int id) throws SQLException {
        String sql = "DELETE FROM students WHERE id = ?";
        try (PreparedStatement ps = connection.prepareStatement(sql)) {
            ps.setInt(1, id);
            ps.executeUpdate();
        }
    }

    private Student mapRow(ResultSet rs) throws SQLException {
        return new Student(
            rs.getInt("id"),
            rs.getString("name"),
            rs.getString("email"),
            rs.getInt("age"),
            rs.getString("course")
        );
    }
}

StudentService.java (Business Logic)

Example

Controller Layer

StudentController.java (Servlet)

Example

View Layer

student-list.jsp

jsp example

<%@ page contentType="text/html;charset=UTF-8" %>
<%@ taglib uri="jakarta.tags.core" prefix="c" %>

<!DOCTYPE html>
<html>
<head><title>Student Management</title></head>
<body>
    <h2>Students (${totalCount})</h2>
    
    <c:if test="${not empty sessionScope.message}">
        <p style="color:green">${sessionScope.message}</p>
        <c:remove var="message" scope="session" />
    </c:if>
    
    <a href="${pageContext.request.contextPath}/students/add">Add New Student</a>
    
    <table border="1">
        <tr>
            <th>ID</th><th>Name</th><th>Email</th>
            <th>Age</th><th>Course</th><th>Actions</th>
        </tr>
        <c:forEach var="student" items="${students}">
            <tr>
                <td>${student.id}</td>
                <td>${student.name}</td>
                <td>${student.email}</td>
                <td>${student.age}</td>
                <td>${student.course}</td>
                <td>
                    <a href="${pageContext.request.contextPath}/students/edit?id=${student.id}">Edit</a>
                    <a href="${pageContext.request.contextPath}/students/delete?id=${student.id}"
                       onclick="return confirm('Delete this student?')">Delete</a>
                </td>
            </tr>
        </c:forEach>
    </table>
</body>
</html>

student-form.jsp

jsp example

<%@ page contentType="text/html;charset=UTF-8" %>
<%@ taglib uri="jakarta.tags.core" prefix="c" %>

<!DOCTYPE html>
<html>
<head><title>${empty student ? "Add" : "Edit"} Student</title></head>
<body>
    <h2>${empty student ? "Add New" : "Edit"} Student</h2>
    
    <c:if test="${not empty error}">
        <p style="color:red">${error}</p>
    </c:if>
    
    <form method="POST" action="${pageContext.request.contextPath}/students/${empty student ? 'add' : 'edit'}">
        <c:if test="${not empty student}">
            <input type="hidden" name="id" value="${student.id}" />
        </c:if>
        
        <label>Name:</label><br>
        <input type="text" name="name" value="${student.name}" required /><br><br>
        
        <label>Email:</label><br>
        <input type="email" name="email" value="${student.email}" required /><br><br>
        
        <label>Age:</label><br>
        <input type="number" name="age" value="${student.age}" min="16" max="60" required /><br><br>
        
        <label>Course:</label><br>
        <select name="course">
            <option value="Java" ${student.course == 'Java' ? 'selected' : ''}>Java</option>
            <option value="Python" ${student.course == 'Python' ? 'selected' : ''}>Python</option>
            <option value="Web Development" ${student.course == 'Web Development' ? 'selected' : ''}>Web Development</option>
        </select><br><br>
        
        <button type="submit">Save</button>
        <a href="${pageContext.request.contextPath}/students/list">Cancel</a>
    </form>
</body>
</html>

Front Controller Pattern

A Front Controller is a single servlet that handles ALL requests and dispatches to appropriate handlers:

java example

@WebServlet("/app/*")
public class FrontController extends HttpServlet {

    private Map<String, RequestHandler> handlers = new HashMap<>();

    @Override
    public void init() {
        handlers.put("/students", new StudentHandler());
        handlers.put("/courses", new CourseHandler());
        handlers.put("/reports", new ReportHandler());
    }

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        
        String path = request.getPathInfo();
        RequestHandler handler = findHandler(path);
        
        if (handler != null) {
            handler.handle(request, response);
        } else {
            response.sendError(404);
        }
    }
}

This is essentially what Spring MVC's DispatcherServlet does!

Project Structure (MVC)

MVC Benefits Summary

Benefit	Explanation
Separation of Concerns	Each layer has one job
Testability	Model and Service tested independently
Parallel Development	Frontend/Backend developers work separately
Reusability	Models reused across different views
Maintainability	Change view without touching logic
Scalability	Easy to add new features

Interview Key Points

MVC separates data (Model), UI (View), and logic (Controller)
In Java web apps: Model=JavaBeans, View=JSP, Controller=Servlet
Controller receives request, calls Model, forwards to View
JSP pages should NEVER be directly accessible (put in WEB-INF)
Front Controller pattern = single entry point for all requests
Spring MVC is a sophisticated implementation of this pattern
DAO pattern separates database logic from business logic

Summary

In this chapter, we learned about MVC Architecture in detail. Here are the key points:

Basic introduction to the concept and why it is needed
Syntax and structure with complete examples
Internal working and best practices
Real-world applications and use cases
Common mistakes and how to avoid them
How this topic is asked in interviews

To practice these concepts, write and run the code in your IDE and verify the output. Modify each example and experiment so that you deeply understand the concept.

Key Takeaways for Mvc Architecture

This topic is fundamental in Java development and is frequently asked in interviews
Make sure to do hands-on practice for practical implementation
Understanding its use in real-world projects is important for writing production-ready code
Keep referring to documentation and official Java docs for the latest updates
Also develop testing and debugging skills alongside this topic
Follow industry best practices and actively participate in code reviews

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for MVC Architecture.

Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this Java Master Course topic.

Search Terms

java-master-course, java master course, java, master, course, servlets, jsp, mvc

Continue learning this concept

PreviousJSP Tags and JSTL NextRequest and Response Objects