package coreservlets; import java.io.*; import javax.servlet.*; import javax.servlet.http.*; import java.sql.*; /** A servlet that reads information from a database and * presents it in an HTML table. It uses connection * pooling to optimize the database retrieval. A good * test case is ConnectionPool.html, which loads many * copies of this servlet into different frame cells. *

* Taken from Core Servlets and JavaServer Pages * from Prentice Hall and Sun Microsystems Press, * http://www.coreservlets.com/. * © 2000 Marty Hall; may be freely used or adapted. */ public class ConnectionPoolServlet extends HttpServlet { private ConnectionPool connectionPool; public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String table; try { String query = "SELECT firstname, lastname " + " FROM employees WHERE salary > 70000"; Connection connection = connectionPool.getConnection(); DBResults results = DatabaseUtilities.getQueryResults(connection, query, false); connectionPool.free(connection); table = results.toHTMLTable("#FFAD00"); } catch(Exception e) { table = "Error: " + e; } response.setContentType("text/html"); // Prevent the browser from caching the response. See // Section 7.2 of Core Servlets and JSP for details. response.setHeader("Pragma", "no-cache"); // HTTP 1.0 response.setHeader("Cache-Control", "no-cache"); // HTTP 1.1 PrintWriter out = response.getWriter(); String title = "Connection Pool Test"; out.println(ServletUtilities.headWithTitle(title) + "\n" + "

\n" + table + "\n" + "\n"); } /** Initialize the connection pool when servlet is * initialized. To avoid a delay on first access, load * the servlet ahead of time yourself or have the * server automatically load it after reboot. */ public void init() { int vendor = DriverUtilities.MYSQL; String driver = DriverUtilities.getDriver(vendor); String host = "localhost"; String dbName = "javatest"; String url = DriverUtilities.makeURL(host, dbName, vendor); String username = "javauser"; String password = "javadude"; try { connectionPool = new ConnectionPool(driver, url, username, password, initialConnections(), maxConnections(), true); } catch(SQLException sqle) { System.err.println("Error making pool: " + sqle); getServletContext().log("Error making pool: " + sqle); connectionPool = null; } } public void destroy() { connectionPool.closeAllConnections(); } /** Override this in subclass to change number of initial * connections. */ protected int initialConnections() { return(10); } /** Override this in subclass to change maximum number of * connections. */ protected int maxConnections() { return(50); } }