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Using Gremlin through Java

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okram edited this page Jan 5, 2011 · 42 revisions

Compiling Gremlin from Java

Gremlin makes use of Groovy as its host language. As such, Gremlin.groovy compiles down to a Groovy.class. It is possible to use Gremlin in a Java application. The primary to interact with Gremlin.groovy is through the Gremlin.compile(String gremlin) method. This method creates a Pipe (see Pipes) that can be iterated. An example is provided below.

Graph graph = TinkerGraphFactory.createTinkerGraph();
Pipe pipe = Gremlin.compile("outE.inV.name");
pipe.setStarts(graph.getVertex(1));
for(String name : pipe) {
  System.out.println(name);
}

You can also compile pipelines (as well as evaluate more complex scripts) using the JSR 223 GremlinScriptEngine.

An Introduction to JSR 223

One of the exciting developments that occurred in Java 1.6+ was the creation of a collection of interfaces that allow developers to tie other languages to the Java virtual machine (JSR 223). In this way, these languages, through a standard set of methods, can be used within any Java 1.6+ application. Thus, it’s possible to capitalize on the features of another language when building a Java application. For Java applications that make use of graphs, Gremlin is a prime candidate for inclusion.

The reference implementation of JSR 223 deployed with Java 1.6+ is Mozilla’s JavaScript implementation known as Rhino. Other popular implementations include Jython, JRuby, and Groovy. For an excellent reference to other implementations of JSR 223, please see https://scripting.dev.java.net.

Finally, you can learn more about JSR 223 from the articles below.

Gremlin provides two classes that should be communicated with directly when using the Gremlin virtual machine from within a Java application.

  • GremlinScriptEngine implements ScriptEngine
  • GremlinScriptEngineFactory implements ScriptEngineFactory

The common way in which to use Gremlin through these interfaces is as follows. First add a text file named javax.script.ScriptEngineFactory to your META-INF/services directory (ScriptEngineFactory is a service provider). In that file, add the line com.tinkerpop.gremlin.GremlinScriptEngineFactory. Now, the GremlinScriptEngineFactory is available to the ScriptEngineManager.

ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine engine = manager.getEngineByName("gremlin");
// or, instead of above, simply do:
//       ScriptEngine engine = new GremlinScriptEngineFactory().getScriptEngine();
Graph graph = TinkerGraphFactory.createTinkerGraph();
List results = new ArrayList();
engine.getBindings(ScriptContext.ENGINE_SCOPE).put("g", graph);
engine.getBindings(ScriptContext.ENGINE_SCOPE).put("v", graph.getVertex(1)); 
engine.getBindings(ScriptContext.ENGINE_SCOPE).put("name", "josh");
engine.getBindings(ScriptContext.ENGINE_SCOPE).put("results", results);

...
engine.eval("v.outE.inV{it.name==name} >> results");
String script = "i = 0\n" +
                "for(x in 1..10)\n" +
                "  i++";
engine.eval(script);
engine.eval(new FileReader("script.grm"));
  • ENGINE_SCOPE: Engine scope variables/bindings are visible during the lifetime of a single ScriptEngine and a set of variables is maintained for each engine.
  • GLOBAL_SCOPE: Global scope variables/bindings are visible to all engines created by same ScriptEngineManager. This is a SimpleBindings that allow various ScriptEngine ’s created from the same manager to communicate with one another through a “blackboard”. For example, global scope bindings in a Groovy engine can be used by a Gremlin engine and vice versa.

To avoid scoping and thus, variable sharing, use

ScriptEngine engine = new GremlinScriptEngine();

  • See the JavaDoc on ScriptEngine for all the methods exposed by GremlinScriptEngine.
  • See the JavaDoc on ScriptEngineFactory for all the methods exposed by GremlinScriptEngineFactory.
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