Emits a Google KML stream of the shortest path between two points. A "point" is a Neo4j node having latitude and and longitude properties. The Neo4j A* algorithm does the work.

Neo4j shortest path

	public void findShortestPath(PrintStream ps, long startNode, long endNode) {
		try {
			RouterService router = Initializer.getApplicationContext().getBean(RouterService.class);
			router.emitShortestPathKML(ps, startNode, endNode);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	public void emitShortestPathKML(PrintStream ps, long keyValueA, long keyValueB)
			throws ApplicationException {
		
		log.info(String.format("Finding least-expensive route from node %d to node %d", keyValueA, keyValueB));
		GraphDatabaseService graphDb = getDbWrapper().getDbRef();

		Index<Node> nodeIndex = graphDb.index().forNodes(DomainConstants.INDEX_NAME);
		Node nodeA = nodeIndex.get(DomainConstants.PROP_NODE_ID, keyValueA)
				.getSingle();
		Node nodeB = nodeIndex.get(DomainConstants.PROP_NODE_ID, keyValueB)
				.getSingle();

		log.info(String.format("nodeA ID %d", nodeA.getId()));
		log.info(String.format("nodeB ID %d", nodeB.getId()));
		
		Transaction tx = graphDb.beginTx();
		try {
			Expander relExpander = Traversal.expanderForTypes(
					DomainConstants.RelTypes.DOMAIN_LINK, Direction.BOTH);

			relExpander.add(DomainConstants.RelTypes.DOMAIN_LINK, Direction.BOTH);

			PathFinder<WeightedPath> shortestPath = GraphAlgoFactory.aStar(relExpander,
					costEval, estimateEval);

			emitCoordinates(ps, shortestPath, nodeA, nodeB);
			
			tx.success();
			
		} finally {
			tx.finish();
		}
	}

	private void emitCoordinates(PrintStream printSteam, PathFinder<WeightedPath> shortestPath, Node nodeA, Node nodeB) {

		WeightedPath path = shortestPath.findSinglePath(nodeA, nodeB);
		
		if (null != path){
			printSteam.println(KMLConstants.KML_LINE_START);
			for (Node node : path.nodes()) {
				
				double lat = (Double) node.getProperty(DomainConstants.PROP_LATITUDE);
				double lon = (Double) node.getProperty(DomainConstants.PROP_LONGITUDE);
				
				printSteam.println(String.format("%f,%f,2300", lon, lat));
			}
			log.info(String.format("Emitted route having shortest path coordinates (%d...%d)", 
				nodeA.getId(), nodeB.getId()));
			printSteam.println(KMLConstants.KML_LINE_END);
		} else {
			log.info(String.format("No route found between coordinates (%d...%d)", nodeA.getId(), 
				nodeB.getId()));
		}
	}