I know that it is some kind of interface for accessing data from different types of sources. When doing research, I bumped into a concept called data source or data source object, which confused me even further.
What is a DAO programmatically, in terms of where and how it is used?
The Data Access Object is basically an object or an interface that provides access to an underlying database or any other persistence storage.
That definition from: http://en.wikipedia.org/wiki/Data_access_object
Check also the sequence diagram here: http://www.oracle.com/technetwork/java/dataaccessobject-138824.html
Maybe a simple example can help you understand the concept:
Let's say we have an entity to represent an employee:
public class Employee {
private int id;
private String name;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
The employee entities will be persisted into a corresponding Employee table in a database.
A simple DAO interface to handle the database operation required to manipulate an employee entity will be like:
interface EmployeeDAO {
List<Employee> findAll();
List<Employee> findById();
List<Employee> findByName();
boolean insertEmployee(Employee employee);
boolean updateEmployee(Employee employee);
boolean deleteEmployee(Employee employee);
}
Next we have to provide a concrete implementation for that interface to deal with SQL server, and another to deal with flat files, etc.