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18.6 Prepared Statements (Precompiled Queries)

497

Listing 18.17 ExitListener.java 

package coreservlets;

import java.awt.*;

import java.awt.event.*;

/** A listener that you attach to the top level Frame

 *  or JFrame of your application, so quitting the

 *  frame exits the application.

*/

public class ExitListener extends WindowAdapter {

  public void windowClosing(WindowEvent event) {

    System.exit(0);

  }

}

18.6 Prepared Statements 

(Precompiled Queries)

If you are going to execute similar SQL statements multiple times, using

 prepared  statements can be more efficient than executing a raw query each

time. The idea is to create a parameterized statement in a standard form that

is sent to the database for compilation before actually being used. You use a

question mark to indicate the places where a value will be substituted into

the statement. Each time you use the prepared statement, you simply replace

some of the marked parameters, using a 

setXxx

 call corresponding to the

entry you want to set (using 1 based indexing) and the type of the parameter

(e.g., 

setInt

, 

setString

, and so forth). You then use 

executeQuery

 (if you

want a 

ResultSet

 back) or 

execute

/

executeUpdate

 (for side effects) as

with normal statements. For instance, if you were going to give raises to all

the personnel in the 

employees

 database, you might do something like the

following:

Connection connection =

DriverManager.getConnection(url, user, password);

String template = 

"UPDATE employees SET salary = ? WHERE id = ?";

PreparedStatement statement =

connection.prepareStatement(template);

float[] newSalaries = getNewSalaries();

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

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