JDBC (Java Database Connectivity)

JDBC is an API that allows Java to interact with databases like MySQL, PostgreSQL, and Oracle.

Architecture

1. Java Application: Your code.
2. JDBC Driver: Library specific to the DB (e.g., mysql-connector-java).
3. Database: The actual storage.

Steps to Connect

1. Load Driver: Class.forName("com.mysql.cj.jdbc.Driver");
2. Create Connection: DriverManager.getConnection(url, user, pass);
3. Create Statement: con.createStatement();
4. Execute Query: stmt.executeQuery(sql);
5. Process ResultSet: Loop through data.
6. Close Connection.

Code Example

import java.sql.*;

public class Main {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/mydb";
        String user = "root";
        String pass = "password";

        try {
            Connection con = DriverManager.getConnection(url, user, pass);
            Statement stmt = con.createStatement();
            ResultSet rs = stmt.executeQuery("SELECT * FROM users");

            while(rs.next()) {
                System.out.println(rs.getString("username"));
            }
            con.close();
        } catch (Exception e) {
            System.out.println(e);
        }
    }
}

[!WARNING] Always assume user input is malicious! Use PreparedStatement to prevent SQL Injection.

PreparedStatement

Unlike Statement, PreparedStatement pre-compiles the SQL and accepts parameters safely.

PreparedStatement pstmt = con.prepareStatement("SELECT * FROM users WHERE id = ?");
pstmt.setInt(1, 101);
ResultSet rs = pstmt.executeQuery();

Quiz

Next Steps

Raw JDBC is verbose. In Module 16, we'll see how Spring Boot makes this painless.