JDBC Basics

Most real-world Java applications do not store data only in memory. They interact with databases to store, retrieve, and update information.

JDBC (Java Database Connectivity) is the API that allows Java applications to communicate with databases in a standard and reliable way.

What Is JDBC?

JDBC is a Java API that enables Java programs to:

• Connect to a database
• Execute SQL queries
• Retrieve and manipulate data
• Work with multiple database systems

It acts as a bridge between Java code and the database.

Why JDBC Is Important

Almost every backend system depends on databases. JDBC is the foundation for database access in Java.

It is widely used in:

• Enterprise applications
• Web applications
• Banking and financial systems
• ERP and CRM platforms

How JDBC Works (High-Level)

JDBC follows a simple workflow:

• Load the database driver
• Establish a connection
• Create a statement
• Execute SQL queries
• Process results
• Close the connection

JDBC Architecture

JDBC consists of the following key components:

• Driver – connects Java to the database
• Connection – represents an active database session
• Statement – sends SQL queries to the database
• ResultSet – stores query results

Loading the JDBC Driver

Before connecting to a database, the appropriate JDBC driver must be loaded.

Class.forName("com.mysql.cj.jdbc.Driver");

Modern JDBC versions often load drivers automatically.

Establishing a Database Connection

The DriverManager class is used to create a database connection.

import java.sql.Connection;
import java.sql.DriverManager;

Connection con = DriverManager.getConnection(
    "jdbc:mysql://localhost:3306/testdb",
    "username",
    "password"
);

This connection allows Java to communicate with the database.

Creating a Statement

Once connected, a Statement object is used to execute SQL queries.

import java.sql.Statement;

Statement stmt = con.createStatement();

Executing a Query

You can retrieve data from the database using SQL SELECT queries.

import java.sql.ResultSet;

ResultSet rs = stmt.executeQuery("SELECT * FROM students");

while (rs.next()) {
    System.out.println(rs.getInt("id") + " " + rs.getString("name"));
}

Closing JDBC Resources

Always close database resources to avoid memory leaks.

rs.close();
stmt.close();
con.close();

Real-World Example

Consider a Java application fetching employee records from a database.

ResultSet rs = stmt.executeQuery("SELECT name, salary FROM employees");

while (rs.next()) {
    System.out.println(rs.getString("name") + " - " + rs.getDouble("salary"));
}

This pattern is used across enterprise applications.

Common JDBC Errors

• Incorrect database URL
• Wrong username or password
• Missing JDBC driver
• SQL syntax errors

Best Practices

• Always close connections properly
• Use PreparedStatement for security (covered next)
• Avoid hardcoding credentials
• Handle SQL exceptions carefully

Key Takeaways

• JDBC connects Java applications to databases
• It is the foundation of data-driven Java apps
• Used heavily in enterprise systems

In the next lesson, we will move deeper into JDBC and implement CRUD Operations.