As I do not like XML so much, I spent some time on a very small project to load routes written in JavaScript or Groovy.

Background

When camel runs on top of Spring Boot, it automatically loads routes bounded to spring’s application context as well as xml routes placed in a configurable location so as example, if you add a property like:

camel.springboot.xml-routes = classpath:routes/*.xml

Camel will scan the classpath for resources matching routes/*.xml so can we use a similar approach to load routes written in different languages?

Of course yes.

JavaScript

Java comes with the ScriptEngine so we can use it to invoke a js script that we can use to set up routes. The first attemp was something like:

new RouteBuilder() {
    public void configure() throws Exception {
        ScriptEngineManager manager = ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("nashorn");

        // bind the builder to the script engine
        engine.put("builder", this);

        // evaluate the script
        engine.eval(...);
}

This let us to write a js script such as:

builder.from('timer:js?period=1s')
    .to('log:js?showAll=false&multiline=false')

Yeah it does work but I do not like having to reference a builder directly so I came across this SO question and I re-wrote my code as:

new RouteBuilder() {
    public void configure() throws Exception {
        ScriptEngineManager manager = new ScriptEngineManager();
        ScriptEngine engine = manager.getEngineByName("nashorn");

        // get JavaScript "global" object
        Object global = engine.eval("this");
        // get JS "Object" constructor object
        Object jsObject = engine.eval("Object");

        Invocable invocable = (Invocable) engine;

        // "bind" properties of this to JS global object
        invocable.invokeMethod(jsObject, "bindProperties", global, this);

        // evaluate the script
        engine.eval(...);
    }
}

Which lets to avoid to reference the builder object so we can write our route as:

from('timer:js?period=1s')
    .to('log:js?showAll=false&multiline=false')

Groovy

For groovy I decide not to use the ScriptEngine as Groovy as I did not found any easy way to implement a solution similar to the JavaScript one so I decide Groovy’s native embedding facility:

new RouteBuilder() {
    public void configure() throws Exception {
        CompilerConfiguration cc = new CompilerConfiguration();
        cc.setScriptBaseClass(DelegatingScript.class.getName());

        ClassLoader cl = Thread.currentThread().getContextClassLoader();
        GroovyShell sh = new GroovyShell(cl, new Binding(), cc);

        DelegatingScript script = (DelegatingScript) sh.parse(...)
        script.setDelegate(this);
        script.run();
    }
}

So we can write routes as:

from('timer:groovy?period=1s')
    .process { it.in.body = UUID.randomUUID().toString() }
    .to('log:groovy?showAll=false&multiline=false')

Conclusion

This is a Sunday project so I’m sure there are quite a lot of small details that need some more attention but if you want to experiment with scripting languages instead of XML to define your routes, you can find a small spring boot auto configurer on my GitHub page.

To configure the behavior of the auto configurer you can do something like:

camel:
  springboot:
    # your camel conf here
  routes:
    loader:
      enabled: true
      locations:
        # list of paths and pattern to scan
        # for routes
        - classpath:ext/camel/*.js
        - classpath:ext/camel/*.groovy

Updates (2018-07-30)

I’ve updated the example to include a binding for JavaScript using GraalJS. As there’s no equivalent for nashorn’s bindProperties extension, a little hack is required:

 return new RouteBuilder() {
    public void configure() throws Exception {
        try(Context context = Context.create()) {

            // add this builder instance to javascript language
            // bindings
            context.getBindings("js").putMember("builder", this);

            // move builder's methods to global scope so builder's
            // dsl can be invoke directly
            context.eval(
                "js",
                "m = Object.keys(builder)\n" +
                    "m.forEach((element) => {\n" +
                    "    global[element] = builder[element]\n" +
                    "});"
            );

            // remove bindings
            context.getBindings("js").removeMember("builder");

            try (InputStream is = source.getInputStream()) {
                context.eval(
                    Source.newBuilder("js", new InputStreamReader(is), "").build()
                );
            }
        }
    }
};

To user GraalJS it is required to run the project using GraalVM

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