Data Access Object or DAO design pattern is a popular design pattern to implement persistence layer of Java application. DAO pattern is based on abstraction and encapsulation design principles and shields rest of application from any change on persistence layer e.g. change of database from Oracle to MySQL, change of persistence technology e.g. from File System to Database. For example if you are authenticating user using relational database and later your company wants to use LDAP to perform authentication. If you are using DAO design pattern to access database, it would be relatively safe as you only need to make change on Data Access Layer. DAO design pattern also keeps coupling low between different parts of application. By using DAO design pattern your View Layer is completely independent to DAO layer and only Service layer has dependency on it which is also abstracted by using DAO interface. You can further use Generics to template your DAO layer. If you are using Spring than you can leverage JdbcTemplate for performing JDBC calls which saves lot of boiler plate coding. Using DAO pattern to access database is one of the JDBC best practices to follow.
What is Data Access Object (DAO) pattern in Java
In short Data Access Object or DAO design pattern is way to reduce coupling between Business logic and Persistence logic. Application business logic often needs domain objects which is persisted in either Database, File System or any other persistence storage. DAO pattern allows you to encapsulate code for performing CRUD operation against persistence from rest of application. Which means any change on persistence logic will not affect other layers of application which is already tested. DAO pattern enables application to cope with any change in database provider or persistence technology. In next section we will What are the main benefits of using DAO design pattern in Java application.
Benefits of using DAO design pattern
DAO or Data Access Object design pattern is good example of abstraction and encapsulation object oriented principles. It separates persistence logic is a separate layer called Data access layer which enable application to react safely on change in Persistence mechanism. For example if you shift from File based persistence mechanism to Database, your change will be limited to data access layer and won't impact Service layer or domain Objects. Data Access Object or DAO pattern is pretty much standard in Java application being it core Java, web application or enterprise application. Following are couple of more benefits of using DAO pattern in Java application :
1) DAO design pattern allows JUnit test to run faster as it allows to create Mock and avoid connecting to database to run tests. It improves testing because its easy to write test with Mock objects, rather than an Integration test with database. In case of any issues while running Unit test, you only need to check code and not database. Also shields with database connectivity and environment issues.
2) Since DAO pattern is based on interface, it also promotes Object oriented design principle "programming for interface than implementation" which results in flexible and quality code.
DAO design pattern Example
In the core of Data Access Object or DAO pattern is a Java interface, which defines various method to perform CRUD operation e.g. Create, Read, Update and Delete. Based upon your application back-end technology you can create different implementation of this interface e.g. JdbcDAOImpl to connect database using JDBC, HibernateDAOImple to use hibernate or FileDAOImpl if you are using File system for persistence. Service layer which uses this Data Access Object will use interface to interact with Data access layer. Here is how a typical DAO Interface look like:
it defines various method to perform CRUD operation. Now you can create different implementation of this AccountDAO interface e.g. JdbcAccountDAOImpl or HibernateAccountDAOImpl. Your JdbcAccountDAOImpl will use JDBC API or Spring JdbcTemplate along with SQL Queries to perform CRUD operations.
That's all on what is Data Access Object or DAO pattern in Java and what are benefits of using DAO pattern in Java application. We have also see a simple example of How to implement Data Access Object pattern with AccountDAO interface. It's standard and one of the standard JDBC practices to use DAO pattern to create persistent layer in Java application.
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