How to Connect to a PostgreSQL Database via JDBC in Java

In this tutorial, I’ll walk you through the process of connecting a Java application to a PostgreSQL database using JDBC (Java Database Connectivity). This guide is ideal for beginners who want a hands-on introduction to JDBC in a Maven-based Java project.

✅ Prerequisites

Make sure:

• PostgreSQL is installed and running on your system.
• You have Java and Maven installed.
• You know your database name, username, and password.

1. Create a Maven Project and Add the PostgreSQL JDBC Driver

🛠 Step 1.1 – Create a New Maven Project

You can generate a simple Maven project using the command below:

mvn archetype:generate \
  -DgroupId=com.mycompany.app \
  -DartifactId=my-app \
  -DarchetypeArtifactId=maven-archetype-quickstart \
  -DarchetypeVersion=1.5 \
  -DinteractiveMode=false

🧩 Step 1.2 – Add the PostgreSQL JDBC Driver to pom.xml

Open the pom.xml file and add the following dependency:

<dependency>
    <groupId>org.postgresql</groupId>
    <artifactId>postgresql</artifactId>
    <version>42.7.5</version>
</dependency>

This dependency ensures that the PostgreSQL driver will be downloaded and included in your classpath.

2. Define the Database Connection Details

Inside your Java file (e.g., Main.java), define the JDBC URL, username, and password:

String url = "jdbc:postgresql://localhost:5432/auth_service_db";
String user = "your_username";
String password = "your_password";

🛑 Security Tip: Avoid hardcoding sensitive credentials in production. Use environment variables or a secure config management solution.

3. Establish a Connection to the Database

Wrap your JDBC logic in a try-catch block to handle potential errors gracefully.

try {
    Connection conn = DriverManager.getConnection(url, user, password);

• DriverManager.getConnection() searches for a suitable JDBC driver (which we added via Maven) and attempts to connect using the credentials and URL.

4. Define an SQL Query

Let’s define a simple SQL query to select all records from the users table:

    String query = "SELECT * FROM users";

This assumes you have a table named users in your auth_service_db database.

5. Create a Statement Object

    Statement stmt = conn.createStatement();

• The Statement object allows you to send SQL queries to the database.

6. Execute the Query and Retrieve the Results

    ResultSet rs = stmt.executeQuery(query);

• executeQuery() sends the SQL statement to the database.
• The returned ResultSet holds the data retrieved from the database.

7. Process the Result Set

    while (rs.next()) {
        System.out.println("User: " + rs.getString("username"));
        System.out.println("Password: " + rs.getString("password"));
    }

• rs.next() moves the cursor forward one row at a time.
• You can extract values by passing column names or indexes to getString(), getInt(), etc.

8. Clean Up Resources

Always close resources to avoid memory leaks and connection pool exhaustion.

    rs.close();
    stmt.close();
    conn.close();
} catch (Exception e) {
    e.printStackTrace();
}

🧹 JDBC resources like ResultSet, Statement, and Connection should be closed in reverse order of their creation, preferably in a finally block or using try-with-resources (Java 7+).

💡 Final Code Sample

Here is a complete version for easy reference:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
 
public class Main {
    public static void main(String[] args) {
        String url = "jdbc:postgresql://localhost:5432/auth_service_db";
        String user = "minhduc8a2";
        String password = "123456";
 
        try {
            Connection conn = DriverManager.getConnection(url, user, password);
            String query = "SELECT * FROM users";
            Statement stmt = conn.createStatement();
            ResultSet rs = stmt.executeQuery(query);
 
            while (rs.next()) {
                System.out.println("User: " + rs.getString("username"));
                System.out.println("Password: " + rs.getString("password"));
            }
 
            rs.close();
            stmt.close();
            conn.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

📌 Summary

• JDBC is the standard Java API for database connectivity.
• Use Maven to manage dependencies easily.
• Always handle exceptions and close your resources.
• Avoid hardcoding credentials in real-world applications.

✍️ Author

Le Minh Duc A passionate Java & Spring developer building scalable microservices.