enrollerbean.java

j2ee tutorial

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

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/CollegeDB";
   private SessionContext context;

   public void enroll(String studentId, String courseId) {

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

   public void unEnroll(String studentId, String courseId) {

       try {
          deleteEntry(studentId, courseId);
       } catch (Exception ex) {
           throw new EJBException("unEnroll: " +
              ex.getMessage());
       }
   }

   public void deleteStudent(String studentId) {

       try {
          deleteStudentEntries(studentId);
       } catch (Exception ex) {
           throw new EJBException("deleteStudent: " +
              ex.getMessage());
       }
   }

   public void deleteCourse(String courseId) {

       try {
          deleteCourseEntries(courseId);
       } catch (Exception ex) {
           throw new EJBException("deleteCourse: " +
              ex.getMessage());
       }
   }

   public ArrayList getStudentIds(String courseId) {

       try {
          return selectStudent(courseId);
       } catch (Exception ex) {
           throw new EJBException("getStudentIds: " +
              ex.getMessage());
       }
   }

   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;
   }

} // EnrollerBean