Handle exception thrown in ObjectLoader::doInBackground

As it turns out, SwingWorker still called done, even if the body of the
task itself threw an exception. So it just pushes the open event, even
though `nodes` is null.

What's annoying, is that there doesn't seem to be a good mechanism for
getting that exception... You either need to handle it yourself within
`doInBackground` and then read that exception data in `done`, or abuse
`SwingWorker::get` and catch an `ExecutionException`.

See issue #36 for discovery.

Author: Eswcvlad

src/main/java/com/itextpdf/rups/model/IProgressDialog.java

@@ -69,11 +69,11 @@ public interface IProgressDialog {
     void setTotal(int n);
 
     /**
-     * Displays an error dialog for the given exception.
+     * Displays an error dialog for the given throwable.
      *
-     * @param ex exception to display information about
+     * @param th throwable to display information about
      */
-    void showErrorDialog(Exception ex);
+    void showErrorDialog(Throwable th);
 
     /**
      * Control the visibility of the progress dialog.

src/main/java/com/itextpdf/rups/model/LoggerHelper.java

@@ -52,10 +52,10 @@ private LoggerHelper() {
         // static class
     }
 
-    public static void warn(String message, Exception e, String className) {
+    public static void warn(String message, Throwable th, String className) {
         final Logger logger = LoggerFactory.getLogger(className);
         logger.warn(message);
-        logger.debug(message, e);
+        logger.debug(message, th);
     }
 
     public static void warn(String message, String className) {
@@ -64,8 +64,8 @@ public static void warn(String message, String className) {
         logger.debug(message);
     }
 
-    public static void warn(String message, Exception e, Class<?> c) {
-        warn(message, e, c.getName());
+    public static void warn(String message, Throwable th, Class<?> c) {
+        warn(message, th, c.getName());
     }
 
     public static void warn(String message, Class<?> c) {
@@ -80,10 +80,10 @@ public static void warnf(Language format, Class<?> c, Object... args) {
         warnf(format.getString(), c, args);
     }
 
-    public static void error(String message, Exception e, String className) {
+    public static void error(String message, Throwable th, String className) {
         final Logger logger = LoggerFactory.getLogger(className);
         logger.error(message);
-        logger.debug(message, e);
+        logger.debug(message, th);
     }
 
     public static void error(String message, String className) {
@@ -92,8 +92,8 @@ public static void error(String message, String className) {
         logger.debug(message);
     }
 
-    public static void error(String message, Exception e, Class<?> c) {
-        error(message, e, c.getName());
+    public static void error(String message, Throwable th, Class<?> c) {
+        error(message, th, c.getName());
     }
 
     public static void error(String message, Class<?> c) {
@@ -110,12 +110,12 @@ public static void info(String message, Class<?> c) {
         info(message, c.getName());
     }
 
-    public static void debug(String message, Exception e, String className) {
-        LoggerFactory.getLogger(className).debug(message, e);
+    public static void debug(String message, Throwable th, String className) {
+        LoggerFactory.getLogger(className).debug(message, th);
     }
 
-    public static void debug(String message, Exception e, Class<?> c) {
-        debug(message, e, c.getName());
+    public static void debug(String message, Throwable th, Class<?> c) {
+        debug(message, th, c.getName());
     }
 
     public static void debug(String message, String className) {

src/main/java/com/itextpdf/rups/model/ObjectLoader.java

@@ -44,29 +44,32 @@ This file is part of the iText (R) project.
 
 import com.itextpdf.rups.view.Language;
 
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
 import javax.swing.SwingUtilities;
 import javax.swing.SwingWorker;
 
 /**
  * Loads the necessary iText PDF objects in Background.
  */
-public class ObjectLoader extends SwingWorker<Void, Void> {
+public final class ObjectLoader extends SwingWorker<Void, Void> {
     /**
      * This is the object that wait for task to complete.
      */
-    protected IRupsEventListener eventListener;
+    private final IRupsEventListener eventListener;
     /**
      * RUPS's PdfFile object.
      */
-    protected IPdfFile file;
+    private final IPdfFile file;
     /**
      * The factory that can provide PDF objects.
      */
-    protected IndirectObjectFactory objects;
+    private IndirectObjectFactory objects;
     /**
      * The factory that can provide tree nodes.
      */
-    protected TreeNodeFactory nodes;
+    private TreeNodeFactory nodes;
     /**
      * a human readable name for this loaded
      */
@@ -145,12 +148,47 @@ protected Void doInBackground() {
 
     @Override
     protected void done() {
+        if (handleTaskException()) {
+            return;
+        }
         try {
             eventListener.handleOpenDocument(this);
+            progress.setVisible(false);
         } catch (RuntimeException ex) {
-            progress.showErrorDialog(ex);
-            LoggerHelper.error(ex.getLocalizedMessage(), ex, getClass());
+            displayThrowable(ex);
+        }
+    }
+
+    private boolean handleTaskException() {
+        try {
+            // This will throw an ExecutionException, if doInBackground
+            // threw an exception
+            get(0L, TimeUnit.NANOSECONDS);
+            return false;
+        } catch (ExecutionException e) {
+            displayThrowable(e.getCause());
+            clearResult();
+        } catch (TimeoutException | RuntimeException e) {
+            // This should not happen in practice
+            displayThrowable(e);
+            clearResult();
+        } catch (InterruptedException e) {
+            // This should not happen in practice
+            displayThrowable(e);
+            clearResult();
+            Thread.currentThread().interrupt();
         }
+        return true;
+    }
+
+    private void clearResult() {
+        objects = null;
+        nodes = null;
+    }
+
+    private void displayThrowable(Throwable th) {
+        LoggerHelper.error(th.getLocalizedMessage(), th, getClass());
+        progress.showErrorDialog(th);
         progress.setVisible(false);
     }
 }

src/main/java/com/itextpdf/rups/model/ProgressDialog.java

@@ -158,12 +158,12 @@ public void setTotal(int n) {
     }
 
     /**
-     * Displays an error dialog for the given exception.
+     * Displays an error dialog for the given throwable.
      *
-     * @param ex exception to display information about
+     * @param th throwable to display information about
      */
     @Override
-    public void showErrorDialog(Exception ex) {
-        ErrorDialogPane.showErrorDialog(this, ex);
+    public void showErrorDialog(Throwable th) {
+        ErrorDialogPane.showErrorDialog(this, th);
     }
 }

src/test/java/com/itextpdf/rups/mock/NoopProgressDialog.java

@@ -64,7 +64,7 @@ public void setTotal(int n) {
     }
 
     @Override
-    public void showErrorDialog(Exception ex) {
+    public void showErrorDialog(Throwable th) {
         // noop
     }