Example of dropping a field while parsing

[danvk]

See this StackOverflow question. I'm parsing large GeoJSON files and would like to produce Document objects without the coordinates arrays, which can easily take up 75+% of the space.

I implemented a GenericValue subclass which uses the SAX parser callbacks and its own stack to pull this off. It winds up roughly doubling parsing performance, so this is a very worthwhile optimization. It leaves much to be desired, however: it duplicates large amounts of code from GenericDocument and it's unable to build up objects in exactly the same manner, since methods like GenericValue::SetObjectRaw are private.

@miloyip suggested on StackOverflow that a better way to do this would be with the GenericDocument::Populate method, and that I should file an issue asking for an example. So here I am :)

[miloyip]

Hi,

I have created two examples in #615. Both examples do the same thing, they filter a user-specified key, and then output the filtered results. filterkey just uses SAX API, while filterkeydom firstly populates a DOM, and then output the DOM.

Its usage is like this:

widget.json

{"widget": {
    "debug": "on",
    "window": {
        "title": "Sample Konfabulator Widget",
        "name": "main_window",
        "width": 500,
        "height": 500
    },
    "image": { 
        "src": "Images/Sun.png",
        "name": "sun1",
        "hOffset": 250,
        "vOffset": 250,
        "alignment": "center"
    },
    "text": {
        "data": "Click Here",
        "size": 36,
        "style": "bold",
        "name": "text1",
        "hOffset": 250,
        "vOffset": 100,
        "alignment": "center",
        "onMouseUp": "sun1.opacity = (sun1.opacity / 100) * 90;"
    }
}}

$ filterkey image < widget.json | pretty

{
    "widget": {
        "debug": "on",
        "window": {
            "title": "Sample Konfabulator Widget",
            "name": "main_window",
            "width": 500,
            "height": 500
        },
        "text": {
            "data": "Click Here",
            "size": 36,
            "style": "bold",
            "name": "text1",
            "hOffset": 250,
            "vOffset": 100,
            "alignment": "center",
            "onMouseUp": "sun1.opacity = (sun1.opacity / 100) * 90;"
        }
    }
}

The core thing is the FilterKeyHandler, which receives SAX events, filters them, and forward to the output handler. Both examples uses the same FilterKeyHandler. I think you may implement your own filter for your requirements.