Richard Cannings wrote:
>
> I'm trying to get my applet to do a simple SELECT query. I tried a few
> different ways which usually ended in:
>
> SQLException: java.sql.SQLException: Error during query: null
>
> Finally I gave up, downloaded Daniel Schneider's MySqlQueryApplet.java,
> edited it, and wouldn't you know-- yet another "SQLException:
> java.sql.SQLException: Error during query: null" error.
>
> I searched the mailing list archive but couldn't find any information on
> this. I'm running mm.mysql.jdbc-1.2a, mysql-3.22.23b and
> jdk_1.1.7-v3-glibc-x86-native on a redhat-6.0 linux system. Also with
> the same login@server I can do the query no problem. Any advise would be
> appreciated.
>
> Here is my editted source of Daniel Schneider's MySqlQueryApplet.java:
>
> import org.gjt.mm.mysql.*;
> import org.gjt.mm.mysql.Connection;
> import org.gjt.mm.mysql.Statement;
> import org.gjt.mm.mysql.Driver;
> import org.gjt.mm.mysql.ResultSet;
> import java.applet.Applet;
> import java.awt.Graphics;
> import java.util.Vector;
> import java.sql.*;
>
> public class MySqlQueryApplet 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:mysql://ilaw.math.ucalgary.ca:3306/ilaw";
> // String url = "jdbc:mySubprotocol:myDataSource";
> String query = "select first_name, last_name from users_info";
>
> try {
> Class.forName("org.gjt.mm.mysql.Driver");
> } catch(Exception ex) {
> setError("Can't find Database driver class: " + ex);
> return;
> }
>
> try {
> Vector results = new Vector();
> Connection con = (Connection)
> DriverManager.getConnection(url,"client_user"
> , "_removed_");
> Statement stmt = (Statement) con.createStatement();
> ResultSet rs = (ResultSet)stmt.executeQuery(query);
> while (rs.next()) {
> String s = rs.getString("first_name");
> String s2 = rs.getString("last_name");
> String text = s + " " + s2;
> 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("Who is in the database: ", 5, 10);
> int y = 30;
> java.util.Enumeration enum = queryResults.elements();
> while (enum.hasMoreElements()) {
> String text = (String)enum.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();
> }
> }
Hi Richard
What I can see, is that you load the mm JDBC-driver multiple times (I've never done this,
so perhaps your error comes from that).
Also, in a Applet you should load the JDBC driver with:
Class.forName("org.gjt.mm.mysql.Driver").newInstance();
or with:
DriverManager.registerDriver( new org.gjt.mm.mysql.Driver() );
If this isn't the problem, please send us a stacktrace of the error.
Tschau
Christian
