studentejb.java

J2EE导学

/*
 *
 * Copyright 2000 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the proprietary information of Sun Microsystems, Inc.  
 * Use is subject to license terms.
 * 
 */

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

public class StudentEJB implements EntityBean {

   private String studentId;
   private String name;
   private ArrayList courseIds;
   private Connection con;
   private String dbName = "java:comp/env/jdbc/CollegeDB";
   private EntityContext context;
   private EnrollerHome enrollerHome;

   public ArrayList getCourseIds() {

      System.out.println("in getCourseIds");
      return courseIds;
   }

   public String getName() {

      return name;
   }

   public void setName(String name) {

      this.name = name;
   }

   public String ejbCreate(String studentId, String name)
       throws CreateException {
   
       System.out.println("in ejbCreate");
       try {
          insertStudent(studentId, name);
       } catch (Exception ex) {
           throw new EJBException("ejbCreate: " + 
              ex.getMessage());
       }

       this.studentId = studentId;
       this.name = name;
       System.out.println("about to leave ejbCreate");
       return studentId;
   }
     
   public String ejbFindByPrimaryKey(String primaryKey) 
      throws FinderException {

      boolean result;

      try {
         result = selectByPrimaryKey(primaryKey);
       } catch (Exception ex) {
           throw new EJBException("ejbFindByPrimaryKey: " + 
              ex.getMessage());
       }

      if (result) {
         return primaryKey;
      }
      else {
         throw new ObjectNotFoundException
            ("Row for id " + primaryKey + " not found.");
      }
   }

   public void ejbRemove() {

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

   public void setEntityContext(EntityContext context) {

      System.out.println("in setEntityContext");
      this.context = context;
      courseIds = new ArrayList();
      try {
         makeConnection();
         Context initial = new InitialContext();
         Object objref = initial.lookup("java:comp/env/ejb/Enroller");
         enrollerHome =
             (EnrollerHome)PortableRemoteObject.narrow(objref,
                                           EnrollerHome.class);
      } catch (Exception ex) {
          throw new EJBException("setEntityContext: " +
             ex.getMessage());
      }
   }

   public void unsetEntityContext() {

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

   public void ejbActivate() {

      studentId = (String)context.getPrimaryKey();
   }

   public void ejbPassivate() {

      studentId = null;
   }
   
   public void ejbLoad() {

      System.out.println("in ejbLoad");
      try {
         loadStudent();
         loadCourseIds();
       } catch (Exception ex) {
           throw new EJBException("ejbLoad: " +
              ex.getMessage());
       }
      System.out.println("leaving ejbLoad");
   }

   private void loadCourseIds() {

      System.out.println("in loadCourseIds");
      courseIds.clear();
      System.out.println("in loadCourseIds, about to try");

      try {
         Enroller enroller = enrollerHome.create();
         ArrayList a = enroller.getCourseIds(studentId);
         courseIds.addAll(a);

      } catch (Exception ex) {
          throw new EJBException("Exception in loadCourseIds: " +
             ex.getMessage());
       }
      System.out.println("leaving loadCourseIds");
   }

   public void ejbStore() {

      System.out.println("in ejbStore");
      try {
         storeStudent();
       } catch (Exception ex) {
           throw new EJBException("ejbStore: " +
              ex.getMessage());
       }
      System.out.println("leaving ejbStore");
   }

   public void ejbPostCreate(String studentId, String name) { }

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

   private void makeConnection() throws NamingException, SQLException {

      InitialContext ic = new InitialContext();
      DataSource ds = (DataSource) ic.lookup(dbName);
      con =  ds.getConnection();
   }

   private void insertStudent (String studentId, String name)
       throws SQLException {

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

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

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

   private boolean selectByPrimaryKey(String primaryKey) 
      throws SQLException {

      String selectStatement =
            "select studentid " +
            "from student where studentid = ? ";
      PreparedStatement prepStmt =
            con.prepareStatement(selectStatement);
      prepStmt.setString(1, primaryKey);

      ResultSet rs = prepStmt.executeQuery();
      boolean result = rs.next();
      prepStmt.close();
      return result;
   }

   private void deleteStudent(String studentId) throws SQLException {

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

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

   private void loadStudent() throws SQLException {

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

      prepStmt.setString(1, studentId);

      ResultSet rs = prepStmt.executeQuery();

      if (rs.next()) {
         name = rs.getString(1);
         prepStmt.close();
      }
      else {
         prepStmt.close();
         throw new NoSuchEntityException("Row for studentId " + studentId +
            " not found in database.");
      }
   }

   private void storeStudent() throws SQLException {

      String updateStatement =
            "update student set name =  ? " +
            "where studentid = ?";
      PreparedStatement prepStmt = 
            con.prepareStatement(updateStatement);

      prepStmt.setString(1, name);
      prepStmt.setString(2, studentId);
      int rowCount = prepStmt.executeUpdate();
      prepStmt.close();

      if (rowCount == 0) {
         throw new EJBException("Storing row for studentId " + 
            studentId + " failed.");
      }
   }


} // StudentEJB