Java · Theory

URLConnection class

Theory

185/270

URLConnection class

URLConnection class sits in JDBC — Java talking to a database with SQL. Five steps: driver → Connection → Statement/PreparedStatement → ResultSet → close (try-with-resources).

For URLConnection class — prefer PreparedStatement. Never paste user input into SQL with +. That is SQL injection.

URLConnection class session: connection URL, user, and password. ResultSet is read row by row with next(). Close everything when done.

Let's take this on the board with one tiny Main class — no extra files. URLConnection class — this Main really runs. If MySQL school DB is up, it prints Connected to school DB. If not, catch prints No DB yet + exception class. Steps stay: connect → prepare → execute → read → close. Start from main, go line by line, and stop at each print. That output is the proof for URLConnection class.

Exam tip

List the 5 classic JDBC steps in order.

Example

import java.sql.DriverManager;
import java.sql.SQLException;

public class Main {
  public static void main(String[] args) {
    String url = "jdbc:mysql://localhost:3306/school";
    try {
      DriverManager.getConnection(url, "root", "secret");
      System.out.println("Connected to school DB");
    } catch (SQLException e) {
      System.out.println("No DB yet: " + e.getClass().getSimpleName());
    }
  }
}

URLConnection class — this Main really runs. If MySQL school DB is up, it prints Connected to school DB. If not, catch prints No DB yet + exception class. Steps stay: connect → prepare → execute → read → close.

Short notes

DefURLConnection class — JDBC = Java API to talk to a database with SQL.
FlowURLConnection class — driver → Connection → Statement → ResultSet → close.
RuleURLConnection class — prefer PreparedStatement. Use try-with-resources.
TrapURLConnection class — string-concatenating user input into SQL.

import java.sql.DriverManager; import java.sql.SQLException; public class Main { public static void main(String[] args) { String url = "jdbc:mysql://localhost:3306/school"; try { DriverManager.getConnection(url, "root", "secret"); System.out.println("Connected to school DB"); } catch (SQLException e) { System.out.println("No DB yet: " + e.getClass().getSimpleName()); } } }

URLConnection class

Example

Short notes

Questions

URLConnection class

Example

Short notes

Questions