Unit 4: Applets, AWT, servlets and JDBC

• Applet: a small Java program embedded in a web page and run by a browser plug-in or appletviewer. Applets are now obsolete — browsers removed plug-in support, appletviewer was dropped in JDK 11 and the Applet API is deprecated — but the concepts carry over to GUI programming and remain in the syllabus.

• AWT (Abstract Window Toolkit) uses native, heavyweight components; Swing (JFrame, JButton) adds lightweight, richer components and is preferred for new desktop code.

java@WebServlet("/hello")
public class Hello extends HttpServlet {
    protected void doPost(HttpServletRequest req, HttpServletResponse res) throws IOException {
        String name = req.getParameter("name");
        res.setContentType("text/html");
        res.getWriter().println("<h2>Welcome, " + name + "</h2>");
    }
}

• GET sends data in the URL (bookmarkable, limited); POST sends it in the body (forms, larger data).

• Other techniques: URL rewriting and hidden form fields.

javaString url = "jdbc:mysql://localhost:3306/college";
try (Connection con = DriverManager.getConnection(url, "root", "pwd");
     PreparedStatement ps = con.prepareStatement("SELECT name FROM student WHERE marks > ?")) {
    ps.setInt(1, 60);
    ResultSet rs = ps.executeQuery();
    while (rs.next()) System.out.println(rs.getString("name"));
    PreparedStatement up = con.prepareStatement("UPDATE student SET marks = marks + 5 WHERE id = ?");
    up.setInt(1, 7); up.executeUpdate();
}

• PreparedStatement prevents SQL injection and is precompiled.