?? indylist.java
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/* * @(#)IndyList.java * * Copyright (c) 1998 Karl Moss. All Rights Reserved. * * You may study, use, modify, and distribute this software for any * purpose provided that this copyright notice appears in all copies. * * This software is provided WITHOUT WARRANTY either expressed or * implied. * * @author Karl Moss * @version 1.0 * @date 04Apr98 * */package javaservlets.db;import javax.servlet.*;import javax.servlet.http.*;import java.sql.*;/** * <p>This is a simple servlet that will use JDBC to gather all * of the Indy 500 winner information from a database and format it * into an HTML table. This servlet uses HttpSessions to keep * track of the position within the ResultSet so that the * table can be split into several different pages, each with * a 'Next n rows' link. */public class IndyList extends HttpServlet{ /** * <p>Performs the HTTP GET operation * * @param req The request from the client * @param resp The response from the servlet */ public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, java.io.IOException { // Get the last year shown on the page that // called us. Remember that we are sorting // the years in descending order. String lastYear = req.getParameter("lastYear"); if (lastYear == null) { lastYear = "9999"; } // Get our URI String uri = req.getRequestURI(); // Set the content type of the response resp.setContentType("text/html"); // Create a PrintWriter to write the response java.io.PrintWriter out = new java.io.PrintWriter(resp.getOutputStream()); // Print the HTML header out.println("<html>"); out.println("<head>"); out.println("<title>Indianapolis 500 Winners</title>"); out.println("</head>"); out.println("<h2><center>"); out.println("Indianapolis 500 Winners"); out.println("</center></h2>"); out.println("<br>"); // Create any addition properties necessary for connecting // to the database, such as user and password java.util.Properties props = new java.util.Properties(); props.put("user", ""); props.put("password", ""); query("sun.jdbc.odbc.JdbcOdbcDriver", "jdbc:odbc:MyAccess", props, "SELECT * from IndyWinners where year < " + lastYear + " order by year desc", out, uri); // Wrap up out.println("</html>"); out.flush(); out.close(); } /** * <p>Performs the HTTP POST operation * * @param req The request from the client * @param resp The response from the servlet */ public void doPost(HttpServletRequest req, HttpServletResponse resp) { // Same as get doGet(req, resp); } /** * <p>Initialize the servlet. This is called once when the * servlet is loaded. It is guaranteed to complete before any * requests are made to the servlet * * @param cfg Servlet configuration information */ public void init(ServletConfig cfg) throws ServletException { super.init(cfg); } /** * <p>Destroy the servlet. This is called once when the servlet * is unloaded. */ public void destroy() { super.destroy(); } /** * <p>Given the JDBC driver name, URL, and query string, * execute the query and format the results into an * HTML table * * @param driverName JDBC driver name * @param connectionURL JDBC connection URL * @param props Addition connection properties, such as user * and password * @param query SQL query to execute * @param out PrintWriter to use to output the query results * @param uri Request URI * @return true if the query was successful */ private boolean query(String driverName, String connectionURL, java.util.Properties props, String query, java.io.PrintWriter out, String uri) { boolean rc = true; // The JDBC Connection object Connection con = null; // The JDBC Statement object Statement stmt = null; // The JDBC ResultSet object ResultSet rs = null; // Keep stats for how long it takes to execute // the query long startMS = System.currentTimeMillis(); // Keep the number of rows in the ResultSet int rowCount = 0; try { // Create an instance of the JDBC driver so that it has // a chance to register itself Class.forName(driverName).newInstance(); // Create a new database connection. con = DriverManager.getConnection(connectionURL, props); // Create a statement object that we can execute queries // with stmt = con.createStatement(); // Execute the query rs = stmt.executeQuery(query); // Format the results into an HTML table rowCount = formatTable(rs, out, uri); } catch (Exception ex) { // Send the error back to the client out.println("Exception!"); ex.printStackTrace(out); rc = false; } finally { try { // Always close properly if (rs != null) { rs.close(); } if (stmt != null) { stmt.close(); } if (con != null) { con.close(); } } catch (Exception ex) { // Ignore any errors here } } // If we queried the table successfully, output some // statistics if (rc) { long elapsed = System.currentTimeMillis() - startMS; out.println("<br><i>" + rowCount + " rows in " + elapsed + "ms</i>"); } return rc; } /** * <p>Given a JDBC ResultSet, format the results into * an HTML table * * @param rs JDBC ResultSet * @param out PrintWriter to use to output the table * @param uri Requesting URI * @return The number of rows in the ResultSet */ private int formatTable(java.sql.ResultSet rs, java.io.PrintWriter out, String uri) throws Exception { int rowsPerPage = 10; int rowCount = 0; // Keep track of the last year found String lastYear = ""; // This will be true if there is still more data in the // table boolean more = false; // Create the table out.println("<center><table border>"); // Process the results. First dump out the column // headers as found in the ResultSetMetaData ResultSetMetaData rsmd = rs.getMetaData(); int columnCount = rsmd.getColumnCount(); // Start the table row out.println("<tr>"); for (int i = 0; i < columnCount; i++) { // Create each table header. Note that the column index // is 1-based out.println("<th>" + rsmd.getColumnLabel(i + 1) + "</th>"); } // End the table row out.println("</tr>"); // Now walk through the entire ResultSet and get each // row while (rs.next()) { rowCount++; // Start a table row out.println("<tr>"); // Dump out the values of each row for (int i = 0; i < columnCount; i++) { // Create the table data. Note that the column index // is 1-based String data = rs.getString(i + 1); out.println("<td>" + data + "</td>"); // If this is the year column, cache it if (i == 0) { lastYear = data; } } // End the table row out.println("</tr>"); // If we are keeping track of the maximum number of // rows per page and we have exceeded that count // break out of the loop if ((rowsPerPage > 0) && (rowCount >= rowsPerPage)) { // Find out if there are any more rows after this one more = rs.next(); break; } } // End the table out.println("</table></center>"); if (more) { // Create a 'Next' button out.println("<form method=POST action=\"" + uri + "\">"); out.println("<center>"); out.println("<input type=submit value=\"Next " + rowsPerPage + " rows\">"); out.println("</center>"); // Page was filled. Put in the last year that we saw out.println("<input type=hidden name=lastYear value=" + lastYear + ">"); out.println("</form>"); } return rowCount; }}?? 快捷鍵說明
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