Spring - Perform Update Operation in CRUD

public List<Student> getStudents() throws Exception {
    List<Student> students = new ArrayList<>();
    // the ArrayList students contains
      // all the data from the database
    return students; 
}

package com.jdbc;

public class Student {
    private String name;
    private String gender;
    private String course;
    private int id;
    
    public Student(int id, String name,String course, String gender) {
        this.name = name;
        this.gender = gender;
        this.course = course;
        this.id = id;
    }
    
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getGender() {
        return gender;
    }
    public void setGender(String gender) {
        this.gender = gender;
    }
    public String getCourse() {
        return course;
    }
    public void setCourse(String course) {
        this.course = course;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    @Override
    public String toString() {
        return "Student [id=" + id + ", name" + name + ", course=" + course + ", gender=" + gender + "]";
    }
}

import javax.annotation.Resource;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.DataSource;

import com.jdbc.StudentDbUtil;
import com.jdbc.Student;

@WebServlet("/StudentControllerServlet")
public class StudentControllerServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private StudentDbUtil studentDbUtil;

private void listStudents(HttpServletRequest request, HttpServletResponse response) 
        throws Exception {

        // get students from db util
        // This is where the database arraylist
          // is received in the servlet
        List<Student> students = studentDbUtil.getStudents(); 
        
        // add students to the request
        request.setAttribute("STUDENT_LIST", students);
                
        // send to JSP page (view)
        RequestDispatcher dispatcher =     request.getRequestDispatcher("/CRUDform.jsp");
        
        dispatcher.forward(request, response);
    }
}

@Resource(name="jdbc/test") 
private DataSource dataSource;

@Override 
public void init() throws ServletException { 
    super.init();
      
// create our student db util ... 
// and pass in the conn pool / datasource 
try
{ 
    studentDbUtil = new StudentDbUtil(dataSource); 
} 
catch (Exception exc) {
    throw new ServletException(exc); 
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    try {
    String theCommand = request.getParameter("command");
        
    switch (theCommand) {
      case "LOAD":
          loadStudent(request, response); 
        break;
        }
    }
    catch (Exception exc) {
        throw new ServletException(exc);
    }
}

private void loadStudent(HttpServletRequest request, HttpServletResponse response) 
            throws Exception {
            
    // read student id from form data
    int id = Integer.parseInt(request.getParameter("id"));
    String theStudentId = request.getParameter("studentId");
    String crud = request.getParameter("crud");
    
    // get student from database (db util)
    Student theStudent = studentDbUtil.getStudent(id);   
            
    // get students from db util and control continues            
    List<Student> students = studentDbUtil.getStudents();
            
    // add students to the request
    request.setAttribute("STUDENT_LIST", students);
            
    // place student in the request attribute
    request.setAttribute("THE_STUDENT", theStudent);
            
    request.setAttribute("COMMAND", "update");    

    // send to jsp page: CRUDform.jsp
    RequestDispatcher dispatcher = request.getRequestDispatcher("/CRUDform.jsp");
            
    dispatcher.forward(request, response);        
}

// point of resource injection
public DataSource dataSource; 
     
public StudentDbUtil(DataSource theDataSource) { 
    dataSource = theDataSource;
} 

public Student getStudent(int theStudentId) throws Exception{
        Student theStudent = null;
        
        Connection myConn = null;
        PreparedStatement myStmt = null;
        ResultSet myRs = null;
        String studentId;
        try {
            // get connection to database
            myConn = dataSource.getConnection();
            
            //create sql to get selected student
        String sql = "select * from students where id=?";

        // create prepared statement
        myStmt = myConn.prepareStatement(sql);
            
        // set params
        myStmt.setInt(1, theStudentId);
            
        // execute statement
        myRs = myStmt.executeQuery();
            
        // retrieve data from result set row
        if (myRs.next()) {
            int id = myRs.getInt("id");
            String name = myRs.getString("name");
            String course = myRs.getString("course");
            String gender = myRs.getString("gender");
                
            // create new student object
            theStudent = new Student(id, name, course, gender);
        }
        else {
            throw new Exception("Could not find student id: " + theStudentId);
        }    
        return theStudent;
        }
        finally {
            close(myConn, myStmt, myRs);
        }
    }

private void loadStudent(HttpServletRequest request, HttpServletResponse response) 
            throws Exception {                                                              
            
    // get students from db util and control continues            
    List<Student> students = studentDbUtil.getStudents();
            
    // add students to the request
    request.setAttribute("STUDENT_LIST", students);
            
    // place student in the request attribute. This is what is used to pre-populate the form with data from the database.
    request.setAttribute("THE_STUDENT", theStudent);
    
    // the attribute command is set to update for identification purpose.        
    request.setAttribute("COMMAND", "update");    

    // send to jsp page: CRUDform.jsp
    RequestDispatcher dispatcher = request.getRequestDispatcher("/CRUDform.jsp");
            
    dispatcher.forward(request, response);        
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        try {
            // read the "command" parameter
            String theCommand = request.getParameter("command");
            
            // route to the appropriate method
            switch (theCommand) {
                
            case "UPDATE":
            updateStudent(request, response); 
            break;
                
            }
        catch (Exception exc) {
            throw new ServletException(exc);
        }
        
    }

private void updateStudent(HttpServletRequest request, HttpServletResponse response)
            throws Exception {
            // read student info from form data
            int id = Integer.parseInt(request.getParameter("id"));
            String name = request.getParameter("name");
            String course = request.getParameter("course");
            String gender = request.getParameter("gender");
            // create a new student object
            Student theStudent = new Student(id,name,course,gender);
            
            // perform update on database
            studentDbUtil.updateStudent(theStudent);
            
            // get students from db util
            List<Student> students = studentDbUtil.getStudents();
            
            // add students to the request
            request.setAttribute("STUDENT_LIST", students);
        
            // send them back to the "list students" page
            listStudents(request, response);
    }

public void updateStudent(Student theStudent) throws Exception{
        Connection myConn = null;
        PreparedStatement myStmt = null;
        
        try {
            // get connection to database
            myConn = dataSource.getConnection();
            
            // create SQL update statement
            String sql = "update student "
                    + "set  name=?,gender=?,course=? "
                    + "where id=?";
            
            // prepare statement
            myStmt = myConn.prepareStatement(sql);
            
            //set params
            myStmt.setString(1, theStudent.getName());
            myStmt.setString(2, theStudent.getGender());
            myStmt.setString(3, theStudent.getCourse());
            myStmt.setInt(4, theStudent.getId());    
    
            myStmt.execute();
        }
        finally {
            // clean up JDBC objects
            close(myConn, myStmt, null);
        }
    }