Cannot use a function define in Java code to use in registerFunction

[rjdp]

I had this function in my java code that stringifies json

Function<Object, Object> jsonStringify = x -> {
    try {
        return mapper.writeValueAsString(x);
    } catch (JsonProcessingException e) {
        throw new RuntimeException(e);
    }
};

but I cannot do

expr.registerFunction("jsonsStr",  jsonStringify)

, Javascript version of Jsonata allows this.

[wnm3]

I think because Java is compiled and JavaScript is interpreted we'd have to take a different approach (e.g., needing to specify the class, method, parameter types...). We could create this specific function and add it to the functions available, but that is not very expansive. Another approach would be to allow for a jar file to be registered making its classes and methods available as functions, or a particular class that could be provided (replacing a default class) with functions that could be called.

Each function has a signature that helps JSONata know where it can find parameters (e.g,. from context or solely from what is passed), and describing what is returned. So, there would likely need to be a complementary file describing the functions' names and signatures (allowing us to dynamically reference the class and its methods). There would also be limitations on the types of objects able to be returned (JsonNode derivatives or the primitive classes).

I'd like to hear others' ideas before starting to tackle this requirement. Having a $Stringify function added would solve your immediate problem.

[rjdp]

Hey @wnm3

Any object that can be serialised to JSON (may need to implement JSON serialisable interface .. idk) can be the return value and and dealing with kinds of input can be totally registered function's responsibility ( receive Object type and introspect types and handle accordingly ). I am not sure how challenging this would be to implement in Java as I just starting coding in JAVA.

I am not sure if passing function reference to registerFunction has any technical challenges in Java.

[wnm3]

Doesn't the $string function do what you want?

[wnm3]

@rjdp Java provides introspection API's but we are comparing apples and oranges when discussing Java functions and JavaScript functions. I was assuming you wanted the equivalent feature in Java to register Java functions, not JavaScript functions. It would be nice if there was an architected way to allow people to register Java functions to extend JSONata4Java's capabilities.

Regarding registering a JavaScript function that could be executed in a Java environment (what JSONata4Java uses) is more complex. Otherwise, you could simply use this approach to load the jsonata.js and associated JavaScript called by it and not need the Java version. Selenium provides a JavaScript executor discussed here and there is a ScriptEngine discussed here. It gets complicated when needing to work with the data already being managed in Java to make it available to the script and vice versa.

[msmiths]

@wnm3 There is also the Rhino engine. This is what we initially used in WIoTP before implementing a Java version of JSONata.

[rjdp]

@wnm3 I was talking of registering Java functions, as I mentioned in my first comment. I am actually writing a SMT for kafka connect and the only option I have is JAVA. I think if we can register Java functions that would be best.

I think adding javascript support would be unnecessary burden here

[rjdp]

$string works for me, wow I totally missed this. Thankyou! It solves my problem for now. But yeah being able to register Java function would make this on parity with jsonata-js

[wnm3]

@bluemel -- you were looking at refactoring functions in general. Any thoughts on making it easier for people to register their own extensions (Java classes/methods) to JSONata4Java? As long as the jar is in the classpath, I could see something like:

registerFunction(fct-name, fully-qualified-classname, method-name, signature-string)

where we assume unique static public method name returning a JsonNode, null, or throwing an exception... fct-name would then be addressable using the $fct-name reference.