How to display / edit / save a string using an eclipse text editor into a RCP application?

I figured it out. From Rüdiger Herrmann and greg-449 I was able to build this prototype.

class StringEditorInput implements IStorageEditorInput {

    private IStorage storage;

    public StringEditorInput(IStorage storage) {

        this.storage = Objects.requireNonNull(storage, "Storage object cannot be null.");
    }

    @Override
    public boolean exists() {
        return true;
    }

    @Override
    public IStorage getStorage() throws CoreException {
        return storage;
    }

   /* Uninteresting methods left out for brevity */
}

class StringStorage implements IStorage {

    private String content;

    public StringStorage(String content) {

        this.content = Objects.requireNonNull(content, "The new content string cannot be null.");
    }

    @Override
    public InputStream getContents() throws CoreException {
        return new ByteArrayInputStream(content.getBytes(StandardCharsets.UTF_8));
    }

    /* Uninteresting methods left out for brevity */
}

/**
 * Set the text in the PDDL editor.
 *
 * @param text
 *            PDDL code to show in the editor.
 */
public void setEditorText(String text) {

    String editorId = "pl.poznan.put.cs.gui4pddl.PDDLEditor";
    IWorkbenchPage page = PlatformUI.getWorkbench().getActiveWorkbenchWindow().getActivePage();

    try {
        editor = IDE.openEditor(page, new StringEditorInput(new StringStorage(text)), editorId);
    } catch (PartInitException e) {
        e.printStackTrace();
    }
}

/**
 * Get the text currently displayed in the PDDL editor.
 *
 * @return PDDL code.
 */
public String getEditorText() {

    IWorkbenchPage page = PlatformUI.getWorkbench().getActiveWorkbenchWindow().getActivePage();
    page.saveEditor(editor, false);

    String editorText = "";

    if (editor instanceof ITextEditor) {
        ITextEditor textEditor = (ITextEditor) editor;

        IDocumentProvider provider = textEditor.getDocumentProvider();

        IEditorInput input = editor.getEditorInput();

        IDocument document = provider.getDocument(input);

        editorText = document.get();
    }

    return editorText;
}

Note that setEditorText(String text) and getEditorText() are somehow connected to the buttons Open and Save in my RCP application.