savingsaccountbean.java

卡内基梅隆大学软件工程课件,很全面

/*
 *
 * 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.sql.*;
import javax.sql.*;
import java.util.*;
import java.math.*;
import javax.ejb.*;
import javax.naming.*;

public class SavingsAccountBean implements EntityBean {

    private String id;
    private String firstName;
    private String lastName;
    private BigDecimal balance;
    private EntityContext context;
    private Connection con;
    private String dbName = "java:comp/env/jdbc/SavingsAccountDB";

    public void debit(BigDecimal amount) 
       throws InsufficientBalanceException {

       if (balance.compareTo(amount) == -1) {
           throw new InsufficientBalanceException();
       }
       balance = balance.subtract(amount);
    }

    public void credit(BigDecimal amount) {

       balance = balance.add(amount);
    }
 
    public String getFirstName() {
 
       return firstName;
    }
 
    public String getLastName() {
 
       return lastName;
    }
  
    public BigDecimal getBalance() {

       return balance;
    }

    public void ejbHomeChargeForLowBalance(BigDecimal minimumBalance, 
       BigDecimal charge) throws InsufficientBalanceException {

       try {
           SavingsAccountHome home = (SavingsAccountHome)context.getEJBHome();
           Collection c = home.findInRange(new BigDecimal("0.00"),
               minimumBalance.subtract(new BigDecimal("0.01")));

           Iterator i = c.iterator();

           while (i.hasNext()) {
              SavingsAccount account = (SavingsAccount)i.next();
              if (account.getBalance().compareTo(charge) == 1) {
                 account.debit(charge);
              }
           }

       } catch (Exception ex) {
           throw new EJBException("ejbHomeChargeForLowBalance: " 
               + ex.getMessage());
       } 
    } 

    public String ejbCreate(String id, String firstName, 
       String lastName, BigDecimal balance)
       throws CreateException {

       if (balance.signum() == -1)  {
          throw new CreateException
             ("A negative initial balance is not allowed.");
       }

       try {
          insertRow(id, firstName, lastName, balance);
       } catch (Exception ex) {
           throw new EJBException("ejbCreate: " + 
              ex.getMessage());
       }

       this.id = id;
       this.firstName = firstName;
       this.lastName = lastName;
       this.balance = balance;

       return id;
    }

   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 Collection ejbFindByLastName(String lastName)
      throws FinderException {

      Collection result;

      try {
         result = selectByLastName(lastName);
       } catch (Exception ex) {
           throw new EJBException("ejbFindByLastName " + 
              ex.getMessage());
       }
       return result;
   }

   public Collection ejbFindInRange(BigDecimal low, BigDecimal high)
      throws FinderException {

      Collection result;

      try {
         result = selectInRange(low, high);
            
       } catch (Exception ex) {
           throw new EJBException("ejbFindInRange: " + 
              ex.getMessage());
       }
      return result;
   }

   public void ejbRemove() {

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

   public void setEntityContext(EntityContext context) {

      this.context = context;
      try {
         makeConnection();
      } catch (Exception ex) {
          throw new EJBException("Unable to connect to database. " +
             ex.getMessage());
      }
   }

   public void unsetEntityContext() {

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

   public void ejbActivate() {

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

   public void ejbPassivate() {

      id = null;
   }

   public void ejbLoad() {

      try {
         loadRow();
       } catch (Exception ex) {
           throw new EJBException("ejbLoad: " + 
              ex.getMessage());
       }
   }
   
   public void ejbStore() {

      try {
         storeRow();
       } catch (Exception ex) {
           throw new EJBException("ejbStore: " + 
              ex.getMessage());
       }
   }


   public void ejbPostCreate(String id, String firstName, 
      String lastName, BigDecimal balance) { }


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

   private void makeConnection() throws NamingException, SQLException {

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

   private void insertRow (String id, String firstName, String lastName, 
                           BigDecimal balance) throws SQLException {

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

          prepStmt.setString(1, id);
          prepStmt.setString(2, firstName);
          prepStmt.setString(3, lastName);
          prepStmt.setBigDecimal(4, balance);

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

   private void deleteRow(String id) throws SQLException {

      String deleteStatement =
            "delete from savingsaccount where id = ? ";
      PreparedStatement prepStmt =
            con.prepareStatement(deleteStatement);

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

   private boolean selectByPrimaryKey(String primaryKey) 
      throws SQLException {

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

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

   private Collection selectByLastName(String lastName) 
      throws SQLException {

      String selectStatement =
            "select id " +
            "from savingsaccount where lastname = ? ";
      PreparedStatement prepStmt = 
            con.prepareStatement(selectStatement);

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

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

      prepStmt.close();
      return a;
   }

   private Collection selectInRange(BigDecimal low, BigDecimal high) 
      throws SQLException {

      String selectStatement =
            "select id from savingsaccount " +
            "where balance between  ? and ?";
      PreparedStatement prepStmt = 
            con.prepareStatement(selectStatement);

      prepStmt.setBigDecimal(1, low);
      prepStmt.setBigDecimal(2, high);
      ResultSet rs = prepStmt.executeQuery();
      ArrayList a = new ArrayList();

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

      prepStmt.close();
      return a;
   }

   private void loadRow() throws SQLException {

      String selectStatement =
            "select firstname, lastname, balance " +
            "from savingsaccount where id = ? ";
      PreparedStatement prepStmt = 
            con.prepareStatement(selectStatement);

      prepStmt.setString(1, this.id);

      ResultSet rs = prepStmt.executeQuery();

      if (rs.next()) {
         this.firstName = rs.getString(1);
         this.lastName = rs.getString(2);
         this.balance = rs.getBigDecimal(3);
         prepStmt.close();
      }
      else {
         prepStmt.close();
         throw new NoSuchEntityException("Row for id " + id +
            " not found in database.");
      }
   }


   private void storeRow() throws SQLException {

      String updateStatement =
            "update savingsaccount set firstname =  ? ," +
            "lastname = ? , balance = ? " +
            "where id = ?";
      PreparedStatement prepStmt = 
            con.prepareStatement(updateStatement);

      prepStmt.setString(1, firstName);
      prepStmt.setString(2, lastName);
      prepStmt.setBigDecimal(3, balance);
      prepStmt.setString(4, id);
      int rowCount = prepStmt.executeUpdate();
      prepStmt.close();

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

} // SavingsAccountBean