DAO design pattern is used in the data persistent layer of a Java

application. It mainly uses OOPS principle of Encapsulation.

By using DAO pattern it makes the application loosely coupled and

less dependent on actual database.

We can even implement some in-memory database like H2 with

DAO to handle the unit-testing.

In short, DAO hides the underlying database implementation from

the class that accesses the data via DAO object.

Recently we can combine DAO with Spring framework to inject any

DB implementation.

https://www.digitalocean.com/community/tutorials/dao-design-pattern