JDBC applet
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/**
* This is a demonstration JDBC applet. It displays some simple standard output
* from the Coffee database.
*/
import java.applet.Applet;
import java.awt.Graphics;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Vector;
public class OutputApplet extends Applet implements Runnable {
private Thread worker;
private Vector queryResults;
private String message = "Initializing";
public synchronized void start() {
// Every time "start" is called we create a worker thread to
// re-evaluate the database query.
if (worker == null) {
message = "Connecting to database";
worker = new Thread(this);
worker.start();
}
}
/**
* The "run" method is called from the worker thread. Notice that because
* this method is doing potentially slow databases accesses we avoid making
* it a synchronized method.
*/
public void run() {
String url = "jdbc:mySubprotocol:myDataSource";
String query = "select COF_NAME, PRICE from COFFEES";
try {
Class.forName("myDriver.ClassName");
} catch (Exception ex) {
setError("Can't find Database driver class: " + ex);
return;
}
try {
Vector results = new Vector();
Connection con = DriverManager.getConnection(url, "myLogin",
"myPassword");
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(query);
while (rs.next()) {
String s = rs.getString("COF_NAME");
float f = rs.getFloat("PRICE");
String text = s + " " + f;
results.addElement(text);
}
stmt.close();
con.close();
setResults(results);
} catch (SQLException ex) {
setError("SQLException: " + ex);
}
}
/**
* The "paint" method is called by AWT when it wants us to display our
* current state on the screen.
*/
public synchronized void paint(Graphics g) {
// If there are no results available, display the current message.
if (queryResults == null) {
g.drawString(message, 5, 50);
return;
}
// Display the results.
g.drawString("Prices of coffee per pound: ", 5, 10);
int y = 30;
java.util.Enumeration e = queryResults.elements();
while (e.hasMoreElements()) {
String text = (String) e.nextElement();
g.drawString(text, 5, y);
y = y + 15;
}
}
/**
* This private method is used to record an error message for later display.
*/
private synchronized void setError(String mess) {
queryResults = null;
message = mess;
worker = null;
// And ask AWT to repaint this applet.
repaint();
}
/**
* This private method is used to record the results of a query, for later
* display.
*/
private synchronized void setResults(Vector results) {
queryResults = results;
worker = null;
// And ask AWT to repaint this applet.
repaint();
}
}
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