cardfile.java

有关JDBC的使用一些编程实例,有关与数据库连接的代码

/*
 * Copyright 1996 John Wiley & Sons, Inc. All Rights Reserved. Reproduction
 * or translation of this work beyond that permitted in Section 117 of the 1976
 * United States Copyright Act without the express written permission of the
 * copyright owner is unlawful. Requests for further information should be 
 * addressed to Permissions Department, John Wiley & Sons, Inc. The 
 * purchaser may make back-up copies for his/her own use only and not for 
 * distribution or resale. The Publisher assumes no responsibility for errors, 
 * omissions, or damages, caused by the use of this  software or from the use
 * of the information contained herein.
 *
 */
import java.awt.*;
import java.lang.*;
import java.util.*;
import msql.*;

public class CardFile extends Frame {
  
  // instantiate a new Msql object

  Msql msql = new Msql();

  // the TextField objects for each column

  TextField txt_name, txt_address, txt_city, txt_state, 
            txt_zip, txt_country, txt_phone, txt_id;

  String formstate; // indicates whether we are adding or editing

  //  String    name, address, city, state, zip, country, phone;

  // a layout manager for the Frame

  GridBagLayout layoutmangler = new GridBagLayout();

  // each of the buttons and a Panel to hold them

  Button next, previous, quit, save, newrow, edit, cancel, delete;
  Panel actionbuttons;

  // the Vector holds the primary key (customer id) for
  // each row in the table. currentRow holds the index 
  // of the one we are currently viewing

  int currentRow = 0;
  Vector cardfileKeys = new Vector();

  // this hash is used to map column names to the 
  // corresponding objects (the TextFields)

  Hashtable columnmap = new Hashtable();

  // the default constructor

  public CardFile() {

    // set the layout for the frame
    this.setLayout(layoutmangler);

    // this is the offset within the GridBagLayout. If
    // I want the next object on a different line, I 
    // postincrement. If not, I don't.
    int i = 0;

    // the name field
    //
    // first, I add an anonymous text label to the Frame using
    // the AddToFrame method. Note that it uses column 0, and
    // row i (currently zero). I don't want the textfield
    // to appear on a different row, so I don't postincrement i.

    AddToFrame(new Label("Name:"), 0, i);

    // now, I instantiate txt_name. This is a textfield with 20
    // spaces. Then, I add it to the frame, and insert a reference
    // to it in the columnmap, keyed by 'name', which is the name 
    // of the column in the CardFile table
    
    txt_name = new TextField(20);
    txt_name.setEditable(false);
    AddToFrame(txt_name, 1, i++);
    columnmap.put("name", txt_name);

    // the rest of the fields. Everything is pretty much the same as above.
    //
    // the address field

    AddToFrame(new Label("Address:"), 0, i);
    txt_address = new TextField(35);
    txt_address.setEditable(false);
    AddToFrame(txt_address, 1, i++);
    columnmap.put("address", txt_address);

    // the city field
    // don't postincrement i, so state will show up
    // on the same row.
    
    AddToFrame(new Label("City:"), 0, i);
    txt_city = new TextField(20);
    txt_city.setEditable(false);
    AddToFrame(txt_city, 1, i);
    columnmap.put("city", txt_city);

    // the state field

    AddToFrame(new Label("State:"), 2, i);
    txt_state = new TextField(2);
    txt_state.setEditable(false);
    AddToFrame(txt_state, 3, i++);
    columnmap.put("state", txt_state);

    // the zip field

    AddToFrame(new Label("Zip:"), 0, i);
    txt_zip = new TextField(11);
    txt_zip.setEditable(false);
    AddToFrame(txt_zip, 1, i++);
    columnmap.put("zip", txt_zip);

    // the country field

    AddToFrame(new Label("Country:"), 0, i);
    txt_country = new TextField(25);
    txt_country.setEditable(false);
    AddToFrame(txt_country, 1, i++);
    columnmap.put("country", txt_country);

    // the phone field

    AddToFrame(new Label("Phone:"), 0, i);
    txt_phone = new TextField(20);
    txt_phone.setEditable(false);
    AddToFrame(txt_phone, 1, i++);
    columnmap.put("phone", txt_phone);

    // the id field. 

    AddToFrame(new Label("Id:"), 0, i);
    txt_id = new TextField(4);
    txt_id.setEditable(false);
    AddToFrame(txt_id, 1, i++);
    columnmap.put("id", txt_id);

    // create the button panel and give it a new FlowLayout

    actionbuttons = new Panel();
    actionbuttons.setLayout(new FlowLayout(FlowLayout.CENTER, 5, 5));
    
    // The constraints for the button panel are a little
    // more complex than the constraints for the labels
    // and textfields, so we'll set it up here, and add
    // the actionbuttons panel
    
    GridBagConstraints c = new GridBagConstraints();
    c.gridwidth = 3; c.gridheight = 1;
    c.fill = GridBagConstraints.NONE;
    c.anchor = GridBagConstraints.CENTER;
    c.weightx = 0.0; c.weighty = 0.0;   
    c.gridx = 0; c.gridy = i;
    ((GridBagLayout)this.getLayout()).setConstraints(actionbuttons, c);   
    this.add(actionbuttons);

    // instantiate and add each of the buttons

    previous = new Button("Previous");
    actionbuttons.add(previous);

    next = new Button("Next");
    actionbuttons.add(next);

    quit = new Button("Quit");
    actionbuttons.add(quit);

    newrow = new Button("New");
    actionbuttons.add(newrow);

    edit = new Button("Edit");
    actionbuttons.add(edit);

    delete = new Button("Delete");
    actionbuttons.add(delete);

    // save and cancel are disabled until the user
    // is adding or editing.

    save = new Button("Save");
    actionbuttons.add(save);
    save.setEnabled(false);

    cancel = new Button("Cancel");
    actionbuttons.add(cancel);
    cancel.setEnabled(false);

    // connect to the localhost and use the database
    // named 'sample'

    try {
      msql.Connect("localhost");
      msql.SelectDB("sample");
    } catch(MsqlException e ) {
      e.printStackTrace();      
    }

    // call getKeys() to populate cardfileKeys with unique identifiers
    // for all the keys in the table

    getKeys();

    // call getRow() to display the first row in the table.
    // this should be the element in cardfileKeys at index 
    // currentRow, which starts out at zero.

    getRow();

    // pack the Frame and show it.
    pack();
    show();
    System.out.println("CardFile was started successfully.");

  }

  /**
   * getKeys()
   *
   * This populates the cardfileKeys Vector with unique identifiers
   * for all of the rows in the cardfile table. This lets us buffer
   * all of the rows, without storing the values for each column.
   * As a result, we only have to worry about dirty data if someone
   * changes a key, which of course, you would *never* do...
   *
   * now, if someone else deletes or inserts a row, that's a
   * different problem. Handling that is an excercise left to
   * the reader...
   */
  protected void getKeys() {

    try {

      // delete all the elements in cardfileKeys

      cardfileKeys.removeAllElements();

      // execute a query to get the id column for each of the
      // rows. Then, process each row and add the id column
      // to cardfileKeys

      MsqlResult    result = msql.Query("select id from cardfile");
      String row[];
      while(( row = result.FetchRow()) != null){
	cardfileKeys.addElement(row[0]);
      }

    } 
    catch (MsqlException e) {
      e.printStackTrace();
    }
  }

  /**
   * clearForm()
   *
   * Clear all of the input fields
   *
   */
  protected void clearForm () {

    // blank the name field
    txt_name.setText("");

    // blank the address field
    txt_address.setText("");

    // blank the city field
    txt_city.setText("");

    // blank the state field
    txt_state.setText("");

    // blank the zip field
    txt_zip.setText("");

    // blank the country field
    txt_country.setText("");

    // blank the phone field
    txt_phone.setText("");

    // blank the id field
    txt_id.setText("");

  }

  /**
   * AddToFrame()
   *
   * A convenience method to wrap the living hell
   * that is GridBagConstraints()
   *
   */
  protected void AddToFrame (Component item, int x, int y) {

    // some sane layout defaults.

    GridBagConstraints c = new GridBagConstraints();
    c.gridwidth = 1; c.gridheight = 1;
    c.fill = GridBagConstraints.NONE;
    c.anchor = GridBagConstraints.NORTHWEST;
    c.weightx = 0.0; c.weighty = 0.0;        

    // set the grid coordinates

    c.gridx = x; c.gridy = y;

    // set the constraints, and add the item to the layout

    ((GridBagLayout)this.getLayout()).setConstraints(item, c);    
    this.add(item);

  }


  /**
   *
   * save()
   *
   * Save the record we are editing to the table
   *
   */
  protected void save() {

    // construct an insert statement, with values for each
    // column, including id. Teaching this system to auto-
    // increment id in a multi-user environment is an excercise
    // left up to the reader.
    //
    // Assuming, of course, that bambi hasn't released a version
    // of mSQL which supports this natively :-)

    String sql = "insert into cardfile " +
                 "   (name, address, city, state, zip, country, phone, id)" +
                 "   values ( " + 
                             "'" + txt_name.getText() + "', " +
                             "'" + txt_address.getText() + "', " +
                             "'" + txt_city.getText() + "', " +
                             "'" + txt_state.getText() + "', " +
                             "'" + txt_zip.getText() + "', " +
                             "'" + txt_country.getText() + "', " +
                             "'" + txt_phone.getText() + "', " +
                                   txt_id.getText() + ")";

    try {

      // if the query doesn't throw an exception, we can add the newly
      // created id to the cardfileKeys Vector, and set the currentRow
      // to the element which points to the new record

      MsqlResult    result = msql.Query(sql);
      cardfileKeys.addElement(txt_id.getText());
      currentRow = cardfileKeys.indexOf(txt_id.getText());

      // call getRow() to refresh the form. This really shouldn't
      // be necessary, but it lets us know that the record was
      // saved correctly. Or not, as the case may be :-)

      getRow();

    } 
    catch(MsqlException e ) {
      e.printStackTrace();      
    }
 
  }