Developer Notes - ITwelzel.biz

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AddressDAO ContactsDAO Factory uses accesses selects/creates hsqldb Data Source PersonDAO Contact hsqldb ContactsDAO Client Service accesses Implements accesses CompanyDAO ContactsDAO accesses Figure 1: Implementation of the DAO design pattern for a DAO that accesses data for a business-contacts resource. Developer Notes The DAO Interface Using the DAO pattern, a developer accesses a data source only in terms of its DAO interface. This approach shields the application or client service from modifications to the underlying data source. The following is an example of a DAO interface for a DAO that abstracts data and functionality for a data source that stores information for business contacts: public interface ContactsDAO { public Contact getContact(String personID, String addressID, String companyID) throws DAOException; public String addContact(String addStr) throws DAOException; public void modifyContact(String contactID, String modifyStr) throws DAOException; } public void deleteContact(Contact contact) throws DAOException; 50 www.novell.com/appnotes
The DAO Implementation A DAO interface has at least one concrete class that implements the interface for a specific type of data source. The following is an implementation of the Contacts DAO interface for an hsqldb data source: public class HSQLDBContactsDAO implements ContactsDAO { public static String GET_PERSON_STATEMENT = "select * from person where personID = ?"; public static String GET_ADDRESS_STATEMENT = "select * from address where addressID = ?"; public static String GET_COMPANY_STATEMENT = "select * from company where companyID = ?"; public HSQLDBContactsDAO() { } protected PersonDAO getPerson(String personID) throws DAOException { Connection conn = null; PreparedStatement ps = null; ResultSet rs = null; PersonDAO ret = null; try { conn = getDataSource().getConnection(); ps = conn.prepareStatement(GET_PERSON_STATEMENT, ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY); ps.setString(1, personID); rs = ps.executeQuery(); if (rs.first()) { ret = new HSQLDBPersonDAO(personID, rs); } Developer Notes } rs.close(); ps.close(); conn.close(); return ret; } catch (SQLException se) { throw new DAOException("SQLException: " + se.getMessage()); } protected AddressDAO getAddress(String addressID) throws DAOException { Connection conn = null; PreparedStatement ps = null; ResultSet rs = null; N o v e m b e r 2 0 0 2 51
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