TryCatchRedo

/** Specialized I/O exception to request some kind of user confirmation.
 * A code that needs to ask user shall not attempt to open a dialog itself,
 * rather it shall emit this exception and let its callers show the dialog
 * at appropriate time.
 *
 * @author Jaroslav Tulach
 * @since 2.0
 */
public abstract class UserQuestionException extends IOException {
    /** Description of the dialog to show to the user. Whoever catches
     * this exception shall use 
     * {@link #getQuestionPane()}.
     * {@link JOptionPane#createDialog(java.lang.String)}
     * to construct and display the dialog.
     * 
     * @return the pane to display to user
     */
    public abstract JOptionPane getQuestionPane();
    /** When the user confirms (or rejects) message presented by the
     * {@link #getQuestionPane()} dialog, the exception shall be notified
     * by calling this method with {@link JOptionPane#getValue()} option.
     *
     * @param option the option selected by the user
     */
    public abstract void confirm(Object option);
}
 

try {
    OutputStream os = where.openConnection().getOutputStream();
    os.write(what.toString().getBytes());
    os.close();
} catch (IOException ex) {
    JOptionPane.showMessageDialog(null, ex);
}
 

for (;;) {
    try {
        OutputStream os = where.openConnection().getOutputStream();
        os.write(what.toString().getBytes());
        os.close();
    } catch (UserQuestionException ex) {
        JOptionPane p = ex.getQuestionPane();
        JDialog d = p.createDialog(ex.getLocalizedMessage());
        setVisible(d, p);
        ex.confirm(p.getValue());
        if (
            !p.getValue().equals(JOptionPane.CANCEL_OPTION) &&
            !p.getValue().equals(JOptionPane.CLOSED_OPTION)
        ) {
            continue;
        }
    } catch (IOException ex) {
        JOptionPane.showMessageDialog(null, ex);
    }
    break;
}
 

public final class QueryStream extends OutputStream {
    private ByteArrayOutputStream arr = new ByteArrayOutputStream();
    /** this field can be manipulated by the QueryException */
    Boolean reverse;
 
    @Override
    public synchronized void write(byte[] b, int off, int len)
    throws IOException {
        if (reverse == null) {
            throw new QueryException();
        }
        arr.write(b, off, len);
    }
 
    @Override
    public synchronized void write(int b) throws IOException {
        if (reverse == null) {
            throw new QueryException();
        }
        arr.write(b);
    }
 
    @Override
    public String toString() {
        if (reverse == null) {
            return "Reverse question was not answered yet!";
        }
        if (reverse) {
            StringBuilder sb = new StringBuilder();
            sb.append(arr.toString());
            sb.reverse();
            return sb.toString();
        }
        return arr.toString();
    }
 
    private class QueryException extends UserQuestionException {
 
        @Override
        public JOptionPane getQuestionPane() {
            JOptionPane p = new JOptionPane("Store in reverse way?");
            p.setOptionType(JOptionPane.YES_NO_CANCEL_OPTION);
            return p;
        }
 
        @Override
        public void confirm(Object option) {
            if (option.equals(JOptionPane.YES_OPTION)) {
                reverse = Boolean.TRUE;
                return;
            }
            if (option.equals(JOptionPane.NO_OPTION)) {
                reverse = Boolean.FALSE;
                return;
            }
        }
    }
}
 

Categories: APIDesignPatterns | APIDesignPatterns:Exceptions