FAQ : J2EE Pattern Interview Questions - Data Access Object

Define data access object pattern
Adapt a uniform interface to access multiple databases like relational, unrelational, object-oriented, etc.

Where to use & benefits
Need to access multiple data sources like legacy systems, B2B, LDAP, and so forth.
Lack of uniform APIs to address the requirements to access disparate systems.
Persistent storage APIs vary depending on the product vendor.
Adapt and encapsulate all access to the data source.
Hide the data source implementation details from its clients.
More portable and less code dependencies in components.
Solve differences in the APIs which is used to access different persistent storage mechanisms.
Not useful for container-managed persistence.

Related patterns include

• factory method -- used to deal with different data sources.

• abstract factory -- used to make an abstract layer of access to data sources.

• transfer object -- used to transport data to and from its clients.

Example of Data access object pattern
See sun's code sample