我一直在努力解决SwingWorker的可用性问题,它会在后台任务中抛出任何异常,例如描述了
on this SO thread.该线程给出了一个很好的描述问题,但不讨论恢复原始异常.
我已经交付的小程序需要向上传播异常.但是我还没有抓住它.我正在使用this blog entry中的SimpleSwingWorker包装类来试图解决这个问题.这是一个相当小的班级,但我会在最后转载,仅供参考.
try {
// lots of code here to prepare data,finishing with
SpecialDataHelper helper = new SpecialDataHelper(...stuff...);
helper.execute(); // this will call get+done on the actual worker
} catch (Throwable e) {
// used "Throwable" here in desperation to try and get
// anything at all to match,including unchecked exceptions
//
// no luck,this code is never ever used :-(
}
包装：
class SpecialDataHelper extends SimpleSwingWorker {
public SpecialDataHelper (SpecialData sd) {
this.stuff = etc etc etc;
}
public Void doInBackground() throws Exception {
OurCodeThatThrowsACheckedException(this.stuff);
return null;
}
protected void done() {
// called only when successful
// never reached if there's an error
}
}
SimpleSwingWorker的功能是实际的SwingWorker的done()/ get()方法被自动调用.这在理论上反驳了在后台发生的任何异常.在实践中,没有任何东西被抓住,我甚至不知道为什么.
SimpleSwingWorker类用于引用,为简洁起见没有任何消息：
import java.util.concurrent.ExecutionException;
import javax.swing.SwingWorker;
/**
* A drop-in replacement for SwingWorker<Void,Void> but will not silently
* swallow exceptions during background execution.
*
* Taken from http://jonathangiles.net/blog/?p=341 with thanks.
*/
public abstract class SimpleSwingWorker {
private final SwingWorker<Void,Void> worker =
new SwingWorker<Void,Void>() {
@Override
protected Void doInBackground() throws Exception {
SimpleSwingWorker.this.doInBackground();
return null;
}
@Override
protected void done() {
// Exceptions are lost unless get() is called on the
// originating thread. We do so here.
try {
get();
} catch (final InterruptedException ex) {
throw new RuntimeException(ex);
} catch (final ExecutionException ex) {
throw new RuntimeException(ex.getCause());
}
SimpleSwingWorker.this.done();
}
};
public SimpleSwingWorker() {}
protected abstract Void doInBackground() throws Exception;
protected abstract void done();
public void execute() {
worker.execute();
}
}
解决方法
忘记你的包装,这是吃异常,而SwingWorker没有.以下是应该如何使用SwingWorker,以及如何处理从后台任务抛出的特定异常：
class MeaningOfLifeFinder extends SwingWorker<String,Object> {
@Override
public String doInBackground() throws SomeException {
return findTheMeaningOfLife();
}
@Override
protected void done() { // called in the EDT. You can update the GUI here,show error dialogs,etc.
try {
String meaningOfLife = get(); // this line can throw InterruptedException or ExecutionException
label.setText(meaningOfLife);
}
catch (ExecutionException e) {
Throwable cause = e.getCause(); // if SomeException was thrown by the background task,it's wrapped into the ExecutionException
if (cause instanceof SomeException) {
// TODO handle SomeException as you want to
}
else { // the wrapped throwable is a runtime exception or an error
// TODO handle any other exception as you want to
}
}
catch (InterruptedException ie) {
// TODO handle the case where the background task was interrupted as you want to
}
}
}
