How to use org.eclipse.jface.text

  public String apply(String contents) {
    final TextEdit edit = codeFormatter.format(
        CodeFormatter.K_COMPILATION_UNIT
            | CodeFormatter.F_INCLUDE_COMMENTS, contents, 0,
        contents.length(), 0, Constants.LINE_SEPARATOR);

    if (edit == null) {
      // TODO log a fatal or warning here. Throwing an exception is causing the actual freemarker error to be lost
      return contents;
    }

    IDocument document = new Document(contents);

    try {
      edit.apply(document);
    } catch (Exception e) {
      throw new RuntimeException(
          "Failed to format the generated source code.", e);
    }

    return document.get();
  }
}

public String getHoverInfo(ITextViewer textViewer, IRegion region) {
  try {
    IDocument doc = textViewer.getDocument();
    String text = doc.get(region.getOffset(), region.getLength());
    return "<b>"+text+"</b>";
  } catch (Exception e) {
    return null;
  }        
}

@Override
public void documentAboutToBeChanged(DocumentEvent event) {
  if (fActiveRegion != null) {
    fRememberedPosition= new Position(fActiveRegion.getOffset(), fActiveRegion.getLength());
    try {
      event.getDocument().addPosition(fRememberedPosition);
    } catch (BadLocationException x) {
      fRememberedPosition= null;
    }
  }
}

@Override
public void doubleClicked(ITextViewer text) {
  int offset= text.getSelectedRange().x;
  if (offset < 0)
    return;
  final IDocument document= text.getDocument();
  IRegion region= findExtendedDoubleClickSelection(document, offset);
  if (region == null)
    region= findWord(document, offset);
  if (region != null)
    text.setSelectedRange(region.getOffset(), region.getLength());
}

private void repairRepresentation() {
  if (fActiveRegion == null)
    return;
  int offset= fActiveRegion.getOffset();
  int length= fActiveRegion.getLength();
  fActiveRegion= null;
  // Invalidate ==> remove applied text presentation
  if (fTextViewer instanceof ITextViewerExtension2)
    ((ITextViewerExtension2) fTextViewer).invalidateTextPresentation(offset, length);
  else
    fTextViewer.invalidateTextPresentation();
}

@Override
public int findAndSelect(int widgetOffset, String findString, boolean searchForward, boolean caseSensitive, boolean wholeWord, boolean regExSearch) {
  int modelOffset= widgetOffset == -1 ? -1 : widgetOffset2ModelOffset(widgetOffset);
  if (fRange != null) {
    IRegion range= fRange.getRange();
    modelOffset= TextViewer.this.findAndSelectInRange(modelOffset, findString, searchForward, caseSensitive, wholeWord, range.getOffset(), range.getLength(), regExSearch);
  } else {
    modelOffset= TextViewer.this.findAndSelect(modelOffset, findString, searchForward, caseSensitive, wholeWord, regExSearch);
  }
  widgetOffset= modelOffset == -1 ? -1 : modelOffset2WidgetOffset(modelOffset);
  return widgetOffset;
}

/**
 * Same as {@link #modelRange2WidgetRange(IRegion)} just for a {@link org.eclipse.jface.text.Position}.
 *
 * @param modelPosition the position describing a range in the viewer's document
 * @return a region describing a range in the viewer's widget
 * @since 2.1
 */
protected IRegion modelRange2WidgetRange(Position modelPosition) {
  return modelRange2WidgetRange(new Region(modelPosition.getOffset(), modelPosition.getLength()));
}

@Override
boolean isMultiline(ISelection selection) throws BadLocationException {
  ITextSelection ts= (ITextSelection)selection;
  return fDocument.getLineOfOffset(ts.getOffset()) < fDocument.getLineOfOffset(ts.getOffset() + ts.getLength());
}

private /*static*/ final boolean isVisible(ITextViewer viewer, int offset, int length) {
  if (viewer instanceof ITextViewerExtension5) {
    ITextViewerExtension5 extension= (ITextViewerExtension5) viewer;
    IRegion overlap= extension.modelRange2WidgetRange(new Region(offset, length));
    return overlap != null;
  }
  return viewer.overlapsWithVisibleRegion(offset, length);
}

/**
 * Creates a new document with the given initial content.
 *
 * @param initialContent the document's initial content
 */
public Document(String initialContent) {
  super();
  setTextStore(new CopyOnWriteTextStore(new GapTextStore()));
  setLineTracker(new DefaultLineTracker());
  getStore().set(initialContent);
  getTracker().set(initialContent);
  completeInitialization();
}

@Override
public char getChar(int pos) throws BadLocationException {
  if ((0 > pos) || (pos >= getLength()))
    throw new BadLocationException();
  return getStore().get(pos);
}

@Override
public void documentAboutToBeChanged(DocumentEvent e) {
  if (e.getDocument() == getVisibleDocument())
    fWidgetCommand.setEvent(e);
  handleVisibleDocumentAboutToBeChanged(e);
}

/**
 * Creates a new empty document.
 */
public Document() {
  super();
  setTextStore(new CopyOnWriteTextStore(new GapTextStore()));
  setLineTracker(new DefaultLineTracker());
  completeInitialization();
}

@Override
public void mouseExit(MouseEvent e) {
  if (!hasInformationControlReplacer() || !canMoveIntoInformationControl(getCurrentInformationControl()) || !inKeepUpZone(e.x, e.y, fSubjectControl, fSubjectArea, false)) {
    fMouseLostWhileComputing= true;
    deactivate();
  }
}

@Override
protected void hideInformationControl() {
  try {
    super.hideInformationControl();
  } finally {
    if (fTextViewer instanceof IWidgetTokenOwner) {
      IWidgetTokenOwner owner= (IWidgetTokenOwner) fTextViewer;
      owner.releaseWidgetToken(this);
    }
  }
}

@Override
void replaceInformationControl(boolean takeFocus) {
  if (fTextViewer != null)
    fTextViewer.releaseWidgetToken(this);
  super.replaceInformationControl(takeFocus);
}

@Override
public void doubleClicked(ITextViewer text) {
  int offset= text.getSelectedRange().x;
  if (offset < 0)
    return;
  final IDocument document= text.getDocument();
  IRegion region= findExtendedDoubleClickSelection(document, offset);
  if (region == null)
    region= findWord(document, offset);
  if (region != null)
    text.setSelectedRange(region.getOffset(), region.getLength());
}

/**
 * Creates a new document with the given initial content.
 *
 * @param initialContent the document's initial content
 */
public Document(String initialContent) {
  super();
  setTextStore(new CopyOnWriteTextStore(new GapTextStore()));
  setLineTracker(new DefaultLineTracker());
  getStore().set(initialContent);
  getTracker().set(initialContent);
  completeInitialization();
}

@Override
public char getChar(int pos) throws BadLocationException {
  if ((0 > pos) || (pos >= getLength()))
    throw new BadLocationException();
  return getStore().get(pos);
}

@Override
public String get(int pos, int length) throws BadLocationException {
  int myLength= getLength();
  if ((0 > pos) || (0 > length) || (pos + length > myLength))
    throw new BadLocationException();
  return getStore().get(pos, length);
}