Exception Reporter
In the following code,
public class SomeWidget {
Text fileContent_;
void setup() {
...
dialog_.addSelectionListener(new SelectionListener() {
public void widgetSelected(SelectionEvent e) {
String fileName = dialog_.open();
try {
fileContent_.setText(readFileContents(fileName));
}
catch (IOException e) {
throw new RuntimeException(e);
}
}
...
});
}
readFileContents(String name) throws IOException {/*Some code*/}
}
The readFileContents throws an IOException, which cannot be re-thrown because the SelectionListener is an interface which does not declare a throws clause in the method widgetSelected. Hence, it is not possible to let the user of SomeWidget handle the exception, because even if we throw a RuntimeException, it gets thrown in a Thread that is different from the one that uses SomeWidget.
One solution could be to use Publisher-Subscriber technique for error reporting.
For example:
public class SomeWidget {
Text fileContent_;
void setup() {
...
dialog_.addSelectionListener(new SelectionListener() {
public void widgetSelected(SelectionEvent e) {
String fileName = dialog_.open();
try {
fileContent_.setText(readFileContents(fileName));
}
catch (IOException e) {
reportException(e);
}
}
...
});
}
readFileContents(String name) throws IOException {/*Some code*/}
addExceptionListener(ExceptionListener l) {
excListeners_.add(l);
}
reportException(Throwable t) {
/* Iterate thro' excListeners_ and call exceptionOccurred() */
}
}
public interface ExceptionListener {
void exceptionOccurred(Throwable t);
}
/*
Clients of SomeWidget.
- /
...
SomeWidget s = new SomeWidget();
...
s.addExceptionListener(new ExceptionListener() {
void exceptionOccurred(Throwable t) {
MessageDialog.showDialog(t.getMessage());
}
});
...
This technique allows for more than one handlers to the same exception, centralized error reporting etc.
-- VhIndukumar with Biresh