Developer Notes - ITwelzel.biz

More documents

Recommendations

Info

Introduction This is the sixth in a series of AppNotes outlining a platform and methodology for Java 2 Platform Enterprise Edition (J2EE) application development on NetWare using a service-oriented architecture. In the previous AppNote, we thoroughly examined the platform kernel relating to services that JMX offers to empower our platform. In this AppNote, we will discuss how our platform interfaces with the data tier and how we can build our data-access components to be highly flexible and robust. The Need for Data Access Abstractions The data tier of enterprise application development offers integration and access to all services and data that are prevalent in enterprise applications and systems, including relational databases, directory services, and legacy systems. Developer Notes Direct access to a data source links business logic and implementation details of an external resource. If the API to that resource changes, it will be necessary to also change your application source code throughout the application, resulting in a significant testing and maintenance burden. However, a data access framework that is able to abstract data resources insulates callers from those resource changes. A data access framework presents a vendor-neutral interface to the caller; in addition, it manages the details of passing service requests from the caller to the business tier. This design is particularly beneficial because ultimately a single service request may access multiple data resources. The replacement of an existing data resource will also cause the existing data access class to be replaced, which then presents the new service to the caller. It is effortless for a system design to evolve with time when the business tier (with an abstract data-access layer) is isolated. Overview of JDBC JDBC technology allows you to access nearly any record-oriented data source from the Java programming language. It offers cross-DBMS connectivity to an extensive collection of SQL databases, and also provides access to non-relational data sources, such as spreadsheets or flat files. The JDBC API is the industry standard database-connectivity mechanism between the Java programming language and relational databases. JDBC allows developers the full advantage of Java’s “Write Once, Run Anywhere” promise for cross-platform applications that require access to enterprise data. A JDBC-enabled application allows a developer to effortlessly connect all available relational data, even in a heterogeneous environment. 48 www.novell.com/appnotes
The JDBC API is offered as a core part of the Java 2 platform and makes it possible to establish a connection with a relational database, send SQL statements to the database and process the results. The Data Access Object Pattern Code dependent on specific features of data resources connects business logic and data access logic. Therefore, replacing or modifying an application’s data resources is very complicated. The Data Access Object (DAO) pattern reduces the complications arising from tightly-coupled business logic and data access code by abstracting data sources to enable transparent access to the data. The DAO pattern has the following advantages: • Separates a data resource’s interface from its data access implementation. • Adapts a specific data resource’s access API to a generic interface. • Allows data access implementation to adjust independently from the code that uses the DAO. • Offers access to a particular data resource without coupling the resource’s API to the business logic. • Permits application developers or deployment engineers the choice of a data access mechanism with no changes to the program code. This approach allows a developer access to a data source only in terms of its DAO interface. Based on configuration data, an application uses a factory object to select the DAO implementation at runtime. Developer Notes A DAO interface has at least one concrete class that implements the interface for a specific type of data source. To add a new type of data source, an application developer simply follows the steps listed below: 1. Create a class that implements the DAO interface for the new data source type. 2. Specify the implementing class’s name in a meta-data configuration source. 3. Facilitate a re-initialization by the client service, which causes the creation of an instance of the new DAO class by the factory, which the application will now use. Figure 1 shows the implementation of the DAO design pattern for a DAO that accesses data for a business-contacts resource. Notice how the factory is used to select the DAO implementation. N o v e m b e r 2 0 0 2 49
Page 1: How to Build J2EE Applications Usin
Page 5 and 6: The DAO Implementation A DAO interf
Page 7 and 8: { } throws DAOException String comp
Page 9 and 10: } + e.getMessage()); } return dao;
Page 11 and 12: A Sample XML Configuration sele
Page 13: • For Novell-specific Java progra

Developer Notes - ITwelzel.biz

Create successful ePaper yourself

Delete template?

Save as template?