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From Mark Murphy <jmarkmur...@gmail.com>
Subject Functionality injection technique for XWPF
Date Sun, 16 Oct 2016 00:04:25 GMT
In working through the XWPF API I see a lot of notation concerning
duplicated code. This is because there are a lot of places which need the
same functionality, but they are not related in a way that can easily be
sub-classed. For example a Document Body can contain Comments, Paragraphs
and Tables. So can Headers, Footers, Footnotes, and Table Cells. In
addition, Tables can contain Comments, but not Paragraphs or other Tables.
Same for Table Rows. The content functionality can be sub-classed by
itself, but  many of the objects that need to use that functionality
already have a place in the class structure, and cannot extend another
class. So I need another way to inject that functionality. I have an idea,
but would like some validation from others who are more versed in Java than
I, so here is the thought.

I would create two base content classes: Markup which would contain the
implementation for comments, bookmarks, custom XML, and a few other things
which are used universally throughout the various content parts; and
Content which would extend Markup and add Paragraphs and Tables, and
anything else that is used exclusively where paragraphs and tables can be
added. Both of these would have associated interfaces which would be
implemented in the parts that need this functionality. The part I am not
totally certain about is injecting this functionality into XWPFDocument,
XWPFTable, XWPFTableCell, XWPFHeaderFooter, etc. My thought is to have each
of these objects implement one of the two base content interfaces, and
contain a reference to its associated implementation class. Then to
complete the implementation, it would forward requests associated with
these interfaces to the implementation class.

So XWPFDocument would include something like this:

XWPFDocument extends POIXMLDocument implements IContent

...
private Content _content;
...

public XWPFParagraph createParagraph() {
  return _content.createParagraph();
}
...

I know there are other things I would need to do because the XWPFDocument
class keeps a list of paragraphs and tables, and I would have to update
those lists, but this is the gist of how I would remove the duplication of
implementation details from all the places where it currently exists. A lot
of objects can create paragraphs and tables, and even more can create
comment and bookmark artifacts.

What do you think? Workable? Any cons to this approach?

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