Chapter 6 

275

When you use the EJB container managed persistence technology, you also can

rely on the EJB container's security features to control access to the data. You also

leverage the performance benefits of the EJB container managed persistence

engine, which uses data caching to improve performance. Finally, by using these

technologies, you can take advantage of the mapping tools that come with them. 

The other option for representing relational data is to create a generic layer to

hold the data. For this approach, you use JDBC APIs to handle data from rela 

tional data sources. The JDBC 

RowSet

 technology, in particular, makes it easy to

access relational data in an efficient manner. (Keep in mind, however, that JDBC

RowSet

 technology is not yet standard in the J2EE platform.) The 

RowSet

 technol 

ogy, through the 

WebRowSet

 feature, gives you an XML view of the data source. Its

CachedRowSet

 capabilities lets you access data in a disconnected fashion, while

the 

FilteredRowSet

 functions give you the ability to manage data in a discon 

nected manner, without requiring heavyweight DBMS support. By using a generic

layer to hold data, you have a simpler design, since there is no real layering, and

you avoid the conceptual weight of a formal data model. This approach may have

better performance, particularly when access is tabular in nature (such as when

selecting several attributes from all rows that match a particular condition).

E

To access data stored in non relational data sources, it is best to use connectors. 

Connectors let you plug in non relational data sources to the J2EE environ 

ment. For non relational systems that do not have ready made connectors avail 

able, such as home grown systems, you need to write your own connector. See

 Integrating Custom Legacy Systems  on page 283. 

6.4.2 Data Transformation

Data transformation the ability to convert data to an acceptable application

format is a common requirement for newer applications that need to access legacy

data. Such transformation functionality is necessary because most legacy systems

were not designed to handle the requirements of these subsequent applications. 

To illustrate, a legacy system may store dates using an eight digit integer

format; for example, storing the date September 23, 2003 as 

20030923

. Another

application that accesses this legacy system needs the same date formatted as

either 

MM/DD/YYYY

 or 

09/23/2003

. The application needs to access the eight digit

date from the legacy system and transform it to a usable format.