To use the following examples you need to specify the dependency in your Maven config correctly.
To do routing in your Java code you'll need just a few lines of code.
See this code example on how to do that where also code examples for the next sections are included.
GraphHopper offers three different choices of algorithms for routing: The speed mode (which implements Contraction Hierarchies (CH) and is by far the fastest), the hybrid mode (which uses Landmarks (LM) and is still fast, but also supports some features CH does not support) and the flexible mode (Dijkstra or A*) which does not require calculating index data and offers full flexibility but is a lot slower.
See the profiles for an explanation how to configure the different routing modes. At query time you
can disable speed mode using ch.disable=true. In this case either hybrid mode (if there is an LM preparation for the
chosen profile) or flexible mode will be used. To use flexible mode in the presence of an LM preparation you need to
also set lm.disable=true.
To calculate a route you have to pick one vehicle and optionally an algorithm like
bidirectional_astar, see the test speedModeVersusHybridMode.
The flexible and hybrid modes allow adding a desired heading (north based azimuth between 0 and 360 degree) to any point. Adding a heading makes it more likely that a route starts towards the provided direction, because roads going into other directions are penalized (see the Routing.HEADING_PENALTY parameter and the test headingAndAlternativeRoute).
A heading with the value 'NaN' won't be enforced and a heading not within [0, 360] will trigger an IllegalStateException. It is important to note that if you force the heading at via or end points the outgoing heading needs to be specified. I.e. if you want to force "coming from south" to a destination you need to specify the resulting "heading towards north" instead, which is 0.
The flexible and hybrid mode allows you to calculate alternative routes. Note that this setting can affect speed of your routing requests. See the test headingAndAlternativeRoute and the Parameters class for further hints.
If you want to calculate routes using the GraphHopper Directions API or a self hosted instance of GraphHopper, you can use the Java and Android client-hc (there are also clients for Java Script and many other languages).
GraphHopperAPI gh = new GraphHopperWeb();
gh.load("http://your-graphhopper-service.com");
// or for the GraphHopper Directions API https://graphhopper.com/#directions-api
// gh.load("https://graphhopper.com/api/1/route");
GHResponse rsp = gh.route(new GHRequest(...));