📄 fastemployeelist1.java
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/* * @(#)FastEmployeeList1.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 employee information from a database and format it * into an HTML table. This servlet uses a local connection * pool. */public class FastEmployeeList1 extends HttpServlet{ // Our connection pool. Note that instance variables are // actually global to all clients since there is only // one instance of the servlet that has multiple threads // of execution javaservlets.jdbc.ConnectionPool m_connectionPool; /** * <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 { // 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>Employee List</title>"); out.println("</head>"); out.println("<h2><center>"); out.println("Employees for Nezzer's Chocolate Factory"); out.println("</center></h2>"); out.println("<br>"); out.println("<center>"); out.println("(with local connection pool)"); out.println("</center><br>"); query("SELECT Empno, Name, Position FROM Employee", out); // Wrap up out.println("</html>"); out.flush(); out.close(); } /** * <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); // Create our connection pool m_connectionPool = new javaservlets.jdbc.ConnectionPool(); // Initialize the connection pool. This will start all // of the connections as specified in the connection // pool configuration file try { m_connectionPool.initialize(); } catch (Exception ex) { // Convert the exception ex.printStackTrace(); throw new ServletException ("Unable to initialize connection pool"); } } /** * <p>Destroy the servlet. This is called once when the servlet * is unloaded. */ public void destroy() { // Tear down our connection pool if it was created if (m_connectionPool != null) { m_connectionPool.destroy(); } super.destroy(); } /** * <p>Given the SQL query string, execute the query and * format the results into an HTML table * * @param query SQL query to execute * @param out PrintWriter to use to output the query results * @return true if the query was successful */ private boolean query(String query, java.io.PrintWriter out) { 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 { // Get an available connection from our connection pool con = m_connectionPool.getConnection(); // 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); } 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) { // Put the connection back into the pool m_connectionPool.close(con); } } 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 * @return The number of rows in the ResultSet */ private int formatTable(java.sql.ResultSet rs, java.io.PrintWriter out) throws Exception { int rowCount = 0; // 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 out.println("<td>" + rs.getString(i + 1) + "</td>"); } // End the table row out.println("</tr>"); } // End the table out.println("</table></center>"); return rowCount; }}⌨️ 快捷键说明
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