DAO Design Pattern in Java

DAO Design Pattern in Java

In this article, I am going to discuss the DAO Design Pattern in Java with Examples. Please read our previous article where we discussed the Business Delegate Design Pattern in Java. In this article, we will explore the DAO Design Pattern in Java, its advantages, disadvantages, and practical applications in modern software development.

What is DAO Design Pattern?

In software development, managing data persistence and database interactions can be a complex task. The Data Access Object (DAO) design pattern provides a structured approach to handling data access, abstracting away the underlying database details.

The DAO design pattern separates the business logic of an application from the data access layer, providing a consistent and abstract interface for interacting with a data source, such as a database. It encapsulates the data access operations, hiding the complexities of database connections, SQL queries, and result handling.

Components of DAO Design Pattern

The DAO Design Pattern consists of the following components:

  • Data Access Object (DAO): It is responsible for encapsulating the data access operations, such as creating, reading, updating, and deleting data. The DAO provides a contract or interface that defines the available data access methods, shielding the client from the underlying data access implementation.
  • Data Transfer Object (DTO): It represents the data structure or object used for transferring data between the DAO and the rest of the application. The DTO acts as a container for the data retrieved or updated by the DAO, providing a structured format that can be easily passed between layers.
  • Data Source: It represents the actual data storage, such as a relational database or a file system. The DAO interacts with the data source to perform data access operations, translating the business logic into database-specific queries.
Example to Understand DAO Design Pattern in Java

Let’s consider a real-world example where the DAO design pattern can be applied: an employee management system. Imagine a software application that allows administrators to create, retrieve, update, and delete employee information in a database.

In this scenario, the Data Access Object (DAO) acts as an intermediary between the application and the database, providing a consistent interface for data access operations related to employee management. The DAO encapsulates the details of interacting with the database, such as SQL queries and result handling.

The EmployeeDAO interface defines methods for CRUD (Create, Read, Update, Delete) operations on user entities. It abstracts away the specific database implementation details and provides a contract for the application to interact with the user data. Concrete implementations of the UserDAO interface handle the database-specific operations.

By using the DAO design pattern in this employee management system, the application can separate the employee management logic from the data access operations. The DAO provides a consistent interface for accessing employee data, regardless of the underlying database technology or schema.

The DAO pattern offers advantages such as code reusability, maintainability, and flexibility. Multiple parts of the application can use the UserDAO methods to interact with employee data, promoting code consistency and reducing code duplication. Additionally, changes to the database schema or technology can be isolated within the DAO implementation, minimizing the impact on the rest of the application.

Overall, the DAO design pattern proves valuable in scenarios where there is a need to abstract away the complexities of data access and interact with persistent storage. The user management system example demonstrates how the pattern provides a structured approach to handling employee data, separates concerns, and improves code organization and maintainability. The UML Diagram of this example is given below using DAO Design Pattern.

Example to Understand DAO Design Pattern in Java

Implementing DAO Design Pattern in Java

Step 1: Create a new directory to store all the class files of this project.

Step 2: Open VS Code and create a new project, called dao.

Step 3: In the project, create a new file called Employee.java. Add the following code to the file:

public class Employee
    private int id;
    private String name;

    public Employee(int id, String name)
        this.id = id;
        this.name = 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;}   

To implement the setters, getters, and constructor, you may use the “Source Action…” method found in the right-click menu of VS Code. Other IDEs usually have some similar option to automatically generate setters, getters, and constructors.

Step 4: In the project, create a new file called EmployeeDAO.java. This interface defines the functions that need to be implemented by the concrete class. Add the following code to EmployeeDAO.java:

import java.util.List;

public interface EmployeeDAO
    public List<Employee> getAllEmployees();
    public Employee getEmployeeById (int id);
    public void update (Employee e);
    public void delete (int id);

Step 5: In the project, create a new file called EmployeeDAOImplementation.java. This class implements the functions defined in the aforementioned EmployeeDAO.java. Add the following code to EmployeeDAOImplementation.java:

import java.util.ArrayList;
import java.util.List;

public class EmployeeDAOImplementation implements EmployeeDAO
    private List<Employee> employees;

    public EmployeeDAOImplementation ()
        employees = new ArrayList<>();
        employees.add(new Employee(0, "Employee A"));
        employees.add(new Employee(1, "Employee B"));

    public List<Employee> getAllEmployees()
    {return employees;}

    public Employee getEmployeeById(int id)
    {return employees.get(id);}

    public void update(Employee e)

    public void delete(int id)

Step 6: In the project, create a new file called DAOPatternDemo.java. This class will contain the main() function. Add the following code to DAOPatternDemo.java:

public class DAOPatternDemo
    public static void main(String[] args)
        EmployeeDAO ed = new EmployeeDAOImplementation();

        //print all employees
        for (Employee e : ed.getAllEmployees())
            System.out.println("Employee #" + e.getId() + "\t Name: " + e.getName());
        //update employee
        ed.update(new Employee(1, "Employee C"));

        //check if employee update is successful
        Employee e = ed.getEmployeeById(1);
        System.out.println("Employee #" + e.getId() + "\t Name: " + e.getName());

The main() function creates an object of type EmployeeDAO. It displays all the employee data. Then, it modifies the data of the employee in the controller. Finally, it displays the employee’s data again.

Step 7: Compile and execute the application. Ensure compilation is successful. Verify that the program works as expected.

DAO Design Pattern in Java with Examples

Congratulations! You now know how to implement DAO patterns!

UML Diagram of DAO Design Pattern:

Now, let us see the DAO Design Pattern UML Diagram Components with our Example so that you can easily understand the UML Diagram.

UML Diagram of DAO Design Pattern

The classes can be described as follows:

  1. Object: This is the POJO class.
  2. ObjectDAO: This interface defines the functions that will be later implemented by ObjectDAOImplementation.
  3. ObjectDAOImplementation: This class is responsible for communication between DriverClass and the data.
  4. DriverClass: This class contains the main() function and is responsible for the simulation of the program.
Advantages of Business DAO Pattern in Java:

The followings are the advantages of using the DAO Design Pattern in Java:

  • Separation of Concerns: The DAO design pattern promotes a clear separation of concerns by isolating the data access logic from the rest of the application. It allows developers to focus on business logic without being concerned about the intricacies of database interactions. This separation enhances code readability, maintainability, and testability.
  • Code Reusability: The DAO pattern enables code reusability by encapsulating the data access operations into a separate component. Multiple parts of the application can reuse the DAO methods, eliminating code duplication and ensuring consistency in data access logic. This reusability simplifies development and maintenance, leading to improved code quality.
  • Database Independence: The DAO pattern abstracts away the specific database implementation details, making the application independent of the underlying data source. By encapsulating the SQL queries and database-specific operations within the DAO, it becomes easier to switch or support multiple databases without affecting the client code. This flexibility is particularly useful in scenarios where the application needs to support different database vendors.
  • Enhanced Maintainability: With the DAO design pattern, modifications to the data access layer can be localized within the DAO component. Changes to database schemas, SQL queries, or connection configurations can be made in a centralized manner, minimizing the impact on the rest of the application. This promotes maintainability and simplifies the management of database-related changes.
  • Improved Security: The DAO pattern supports the implementation of security measures, such as data validation, parameterized queries, and access control. By encapsulating the data access logic within the DAO, developers can enforce security practices consistently across the application. This helps prevent SQL injection attacks and ensures data integrity and confidentiality.
Disadvantages of Business DAO Pattern in Java:

The followings are the disadvantages of using the DAO Design Pattern in Java:

  • Increased Complexity: Implementing the DAO design pattern can introduce additional complexity to the application architecture. It requires the creation of DAO interfaces, concrete implementations, and data transfer objects. This added complexity can lead to a larger codebase and increased development effort.
  • Learning Curve: Developers new to the DAO design pattern may face a learning curve, as it requires an understanding of database interactions, SQL queries, and object-relational mapping concepts. Proper training, documentation, and code examples can help mitigate this challenge and facilitate the adoption of the pattern.
  • Potential Performance Overhead: The DAO pattern can introduce some performance overhead, especially in cases where data retrieval involves complex queries or joins. The additional abstraction layer between the application and the database can impact query execution time. Careful optimization and caching strategies may be required to mitigate this potential performance impact.
  • Limited Flexibility for Complex Queries: The DAO pattern works well for simple data access scenarios, but it may not be suitable for complex queries involving multiple joins, aggregations, or stored procedures. In such cases, the DAO may not provide sufficient flexibility to handle advanced query requirements. Custom query execution mechanisms or alternative patterns may be more appropriate.

In the next article, I am going to discuss Front Controller Design Pattern in Java with Examples. Here, in this article, I try to explain DAO Design Pattern in Java with Examples. I hope you understood the need for and use of the DAO Design Pattern in Java.

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