EnrollerBean.java

/**
 *
 * Copyright 2001 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the proprietary information of Sun Microsystems, Inc.  
 * Use is subject to license terms.
 * 
 */

package com.sun.s1peqe.ejb.bmp.enroller.ejb;

import java.rmi.RemoteException; 
import javax.ejb.*;
import java.sql.*;
import javax.sql.*;
import java.util.*;
import javax.naming.*;

public class EnrollerBean implements SessionBean {
 
    private Connection con;
    private String dbName = "java:comp/env/jdbc/bmp-enrollerDB";
    private SessionContext context;

    /**
     * Enrolls a Student in a course
     * @param studentId primary key of the student object
     * @param courseId primary key of the course object
     * @exception RemoteException
     */

    public void enroll(String studentId, String courseId) {
        try {
            insertEntry(studentId, courseId);
        } catch (Exception ex) {
            throw new EJBException("enroll: " + ex.getMessage());
        }
    }

    /**
     * Un-Enrolls a Student in a course
     * @param studentId primary key of the student object
     * @param courseId primary key of the course object
     * @exception RemoteException
     */
    public void unEnroll(String studentId, String courseId) {
        try {
            deleteEntry(studentId, courseId);
        } catch (Exception ex) {
            throw new EJBException("unEnroll: " + ex.getMessage());
        }
    }

    /**
     * Deletes a Student 
     * @param studentId primary key of the student object
     * @exception RemoteException
     */
    public void deleteStudent(String studentId) {
        try {
            deleteStudentEntries(studentId);
        } catch (Exception ex) {
            throw new EJBException("deleteStudent: " + ex.getMessage());
        }
    }

    /**
     * Deletes a Course 
     * @param courseId primary key of the course object
     * @exception RemoteException
     */
    public void deleteCourse(String courseId) {
        try {
            deleteCourseEntries(courseId);
        } catch (Exception ex) {
            throw new EJBException("deleteCourse: " + ex.getMessage());
        }
    }

    /**
     * Returns an Arraylist of StudentsIds enrolled in a course
     * @param courseId primary key of the course object
     * @exception RemoteException
     */
    public ArrayList getStudentIds(String courseId) {
        try {
            return selectStudent(courseId);
        } catch (Exception ex) {
            throw new EJBException("getStudentIds: " + ex.getMessage());
        }
    }

    /**
     * Return an ArrayList of CourseIds that student is enroller in
     * @param studentId primary key of the student object
     * @exception RemoteException
     */
    public ArrayList getCourseIds(String studentId) {
        try {
            return selectCourse(studentId);
        } catch (Exception ex) {
            throw new EJBException("getCourseIds: " + ex.getMessage());
        }
    }

    public void ejbCreate() {
        try {
            makeConnection();
        } catch (Exception ex) {
            throw new EJBException("Unable to connect to database. " +
                                   ex.getMessage());
        }
    }

    public void ejbRemove() {
        try {
            con.close();
        } catch (SQLException ex) {
            throw new EJBException("ejbRemove: " + ex.getMessage());
        }
    }

    public void ejbActivate() {
        try {
            makeConnection();
        } catch (Exception ex) {
            throw new EJBException("ejbActivate Exception: " + ex.getMessage());
        }
    }

    public void ejbPassivate() {
        try {
            con.close();
        } catch (SQLException ex) {
            throw new EJBException("ejbPassivate Exception: " + ex.getMessage());
        }
    }

    public void setSessionContext(SessionContext context) {
        this.context = context;
    }

    public EnrollerBean() {}

    /*********************** Database Routines *************************/

    private void makeConnection() throws NamingException, SQLException {
        InitialContext ic = new InitialContext();
        DataSource ds = (DataSource) ic.lookup(dbName);
        con =  ds.getConnection();
    }

    private void insertEntry(String studentId, String courseId)
        throws SQLException {

        String insertStatement =
            "insert into enrollment values ( ? , ? )";
        PreparedStatement prepStmt = 
            con.prepareStatement(insertStatement);

        prepStmt.setString(1, studentId);
        prepStmt.setString(2, courseId);

        prepStmt.executeUpdate();
        prepStmt.close();
    }

    private void deleteEntry(String studentId, String courseId) 
        throws SQLException {

        String deleteStatement =
            "delete from enrollment " +
            "where studentid = ? and courseid = ?";
        PreparedStatement prepStmt =
            con.prepareStatement(deleteStatement);

        prepStmt.setString(1, studentId);
        prepStmt.setString(2, courseId);
        prepStmt.executeUpdate();
        prepStmt.close();
    }

    private void deleteStudentEntries(String studentId)
        throws SQLException {

        String deleteStatement =
            "delete from enrollment " +
            "where studentid = ?";
        PreparedStatement prepStmt =
            con.prepareStatement(deleteStatement);

        prepStmt.setString(1, studentId);
        prepStmt.executeUpdate();
        prepStmt.close();
    }

    private void deleteCourseEntries(String courseId)
        throws SQLException {

        String deleteStatement =
            "delete from enrollment " +
            "where courseid = ?";
        PreparedStatement prepStmt =
            con.prepareStatement(deleteStatement);

        prepStmt.setString(1, courseId);
        prepStmt.executeUpdate();
        prepStmt.close();
    }

    private ArrayList selectStudent(String courseId) 
        throws SQLException {

        String selectStatement =
            "select studentid " +
            "from enrollment where courseid = ? ";
        PreparedStatement prepStmt = 
            con.prepareStatement(selectStatement);

        prepStmt.setString(1, courseId);
        ResultSet rs = prepStmt.executeQuery();
        ArrayList a = new ArrayList();

        while (rs.next()) {
            String id = rs.getString(1);
            a.add(id);
        }

        prepStmt.close();
        return a;
    }

    private ArrayList selectCourse(String studentId) 
        throws SQLException {

        String selectStatement =
            "select courseid " +
            "from enrollment where studentid = ? ";
        PreparedStatement prepStmt = 
            con.prepareStatement(selectStatement);

        prepStmt.setString(1, studentId);
        ResultSet rs = prepStmt.executeQuery();
        ArrayList a = new ArrayList();

        while (rs.next()) {
            String id = rs.getString(1);
            a.add(id);
        }

        prepStmt.close();
        return a;
    }
}