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18.6 Prepared Statements (Precompiled Queries)

499

Listing 18.18 PreparedStatements.java (continued)

    if (vendor == DriverUtilities.UNKNOWN) {

      printUsage();

      return;

    }

    String driver = DriverUtilities.getDriver(vendor);

    String host = args[0];

    String dbName = args[1];

    String url =

      DriverUtilities.makeURL(host, dbName, vendor);

    String username = args[2];

    String password = args[3];

    // Use "print" only to confirm it works properly,

    // not when getting timing results.

    boolean print = false;

    if ((args.length > 5) && (args[5].equals("print"))) {

      print = true;

    }

    Connection connection =

      getConnection(driver, url, username, password);

    if (connection != null) {

      doPreparedStatements(connection, print);

      doRawQueries(connection, print);

    }

  }

  private static void doPreparedStatements(Connection conn,

                                           boolean print) {

    try {

      String queryFormat =

        "SELECT lastname FROM employees WHERE salary > ?";

      PreparedStatement statement =

        conn.prepareStatement(queryFormat);

      long startTime = System.currentTimeMillis();

      for(int i=0; i<40; i++) {

        statement.setFloat(1, i*5000);

        ResultSet results = statement.executeQuery();

        if (print) {

          showResults(results);

        }

      }

      long stopTime = System.currentTimeMillis();

      double elapsedTime = (stopTime   startTime)/1000.0;

      System.out.println("Executing prepared statement " +

                         "40 times took " +

                         elapsedTime + " seconds.");

    } catch(SQLException sqle) {

      System.out.println("Error executing statement: " + sqle);

    }

  }

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