Buddy... This is really going to be a hard task. Re-Using EditorParts in SWT widgets/ViewParts is not easy. The only thing that I got to manage was to reuse the EPF RichText-Widget which was designed for use as an EditorPart.
In that case it was easy, because it only needed an IEditorSite as a constructor parameter. I then extended it and adapted the IViewSite to an IEditorSite.
But concerning JDT: There is so much funcionality which is directly related to the Base-Text-Editor functionality from eclipses IEditorParts... I think it won't be worth the effort.
Could't you find a Java-IDE for Java-Code? Isn't there anything working with Swing/AWT? You could then possibly include a Source-Code-Editor-Swing-Frame using a SWT_AWT-Brigde-Widget. This way I successfully integrated an Swing-PDF-Viewer into an eclipse ViewPart.
Take a look at the eclipse API desciption.
And as a first rough try for the Java IDE:
drJava