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import java.io.*;
import javax.servlet.*;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.sql.*;
@WebServlet("/DatabaseAccess")
public class Databaseaccess extends HttpServlet {

	private static final long serialVersionUID = 1L;

	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

		// JDBC driver name and database URL
		final String DB_URL_with_SSL = "jdbc:mysql://127.0.0.1:3306/?user=root";

		// Database credentials
		final String USER = "root";
		final String PASS = "denise9955";

		// Set response content type
		response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		String title = "Database Result";

		String docType = "<!doctype html>\n";

		out.println(docType + "<html>\n" + "<head><title>" + title + "</title></head>\n" + "<body>\n" + "<h1>" + title
				+ "</h1>\n");
		try {
			// Register JDBC driver
			Class.forName("com.mysql.cj.jdbc.Driver");

			// Open a connection with a try-with-resources: non c'e' bisogno di chiamare la funzione close su conn, verrà chiusa alla fine del body
			try (Connection conn = DriverManager.getConnection(DB_URL_with_SSL, USER, PASS)) {
				// Execute SQL query
				try (Statement stmt = conn.createStatement()) {
					String sql;
					sql = "SELECT nome, cognome FROM registration where login = 'fsina'";
					try (ResultSet rs = stmt.executeQuery(sql)) {
						// Extract data from result set
						while (rs.next()) {
							// Retrieve by column name
							String first = rs.getString("nome");
							String last = rs.getString("cognome");

							// Display values
							out.println("<h2>Ciao " + first + " ");
							out.println(last + "<h2>");
						}

						out.println("</body></html>");

					}

				}

			}

		} catch (SQLException | ClassNotFoundException e) {
			// Handle errors for JDBC
			e.printStackTrace();
		}
	}
}


MI DA' ERRORE SQL, "DATABASE NOT SELECTED"
why?