Styling features based on a custom rule using GeoTools

Question

I have a Java swing app which loads lines shapefiles which represents a road system. I want to show the congested roads on this map with a separate style.

My current approach

I have two attributes in the shapefile for each line named "DesignCapacity" and "CurrentTraffic". I have a simple rule to check whether the DesignCapacity is less than the CurrentTraffic. The rule is attached to a Line symbolizer which draws the line in a separate color.

LineSymbolizer lineSymbolizer = sb.createLineSymbolizer();
Stroke stroke = sb.createStroke(Color.RED, 4);
lineSymbolizer.setStroke(stroke);
Rule rl = sb.createRule(lineSymbolizer1);
rl.setFilter(sb.getFilterFactory().less(
            sb.getFilterFactory().property("DesignCapacity"), 
            sb.getFilterFactory().property("CurrentTraffic")));
FeatureTypeStyle ft = sb.createFeatureTypeStyle("Feature", rl);
style.featureTypeStyles().add(ft);

return style;

My objective

I would need to add the "DesignCapacity" and "CurrentTraffic" to a separate database thus removing the two attributes from the shapefile. In that case,

1. Can I use the existing rule based styling approach and set a filter? (Instead of shapefile properties, the values should come from database tables)
2. If styling is not the optimum approach, what would be the best way to achieve this?

Answer 1

Your described approach will not work as the styling engine (renderer) only has information about the current feature when it comes to draw it.

The easiest solution is to import your shapefile into your database and then create a view that joins the roads with the table holding your traffic details and use that to draw the map. It will be faster and more flexible too.