Eclipse Pluginで、ファイルに応じたエディタを開く

IFile file = ...;

IEditorDescriptor editorDescriptor = PlatformUI
  .getWorkbench().getEditorRegistry()
  .getDefaultEditor(file.getName());
if (editorDescriptor == null) {
  editorDescriptor = PlatformUI.getWorkbench()
    .getEditorRegistry().getDefaultEditor("file.txt"); //$NON-NLS-1$
}
PlatformUI.getWorkbench().getActiveWorkbenchWindow()
  .getActivePage().openEditor(
    new FileEditorInput(file),
    editorDescriptor.getId());