First step would be read the data from the database. Here is an example using JDBC - Lesson: JDBC Introduction (The Java™ Tutorials > JDBC(TM) Database Access).
Next step is to create a Graphic using the Runtime API. Examples at Add graphics and text to graphics overlays—ArcGIS Runtime SDK for Java (Quartz Beta) | ArcGIS for De...
For example if you have read fields called lat and lng in your database table, then you could create a Graphic like this:
SpatialReference wgs84 = SpatialReferences.getWgs84();
Point location = new Point(lng, lat, wgs84);
SimpleMarkerSymbol marker = new SimpleMarkerSymbol(new RgbColor(255, 0, 0, 255), 10, SimpleMarkerSymbol.Style.CIRCLE);
Graphic graphic = new Graphic(location, marker);
graphicOverlay.getGraphics().add(graphic);