How to format param-signature for a JSNI method with more than 1 parameter?

Question

I am using GWT and have a Java method with a signature that requires a string and a boolean parameter, like this:

private void myMethod(String s, Boolean b) {}

I have a JSNI method that exposes this Java method after compilation:

public class myClass {
    public native void exportMyMethod(myClass c)/*-{
        $wnd.myMethod = $entry(function(s, b) {
            [email protected]::myMethod(Ljava/lang/String;Z);
        });
    }-*/;
}

For the life of me, I cannot figure out how to properly format the param-signature when there's more than 1 parameter.

I've read the GWT documentation regarding how to do this. I've also read where that document directs me to how to properly refer to the JNI Type. But I cannot seem to find an example of how to format the signature when using more than 1 parameter. It seems like it should be easy.

So, how do I format my param-signature correctly? I've tried:

[email protected]::myMethod(Ljava/lang/String;Z);
[email protected]::myMethod(Ljava/lang/String;Ljava/lang/Boolean;);
[email protected]::myMethod(Ljava/lang/StringLjava/lang/Boolean;);
[email protected]::myMethod(Ljava/lang/String;,Ljava/lang/Boolean;);

Every different permutation that I've tried has resulted in the same error.

"Referencing method 'com.path.to.myClass.myMethod(Ljava/lang/String;Z)/' unable to resolve method."

It may be worth noting that I've changed the method signature to only use a single parameter and everything runs fine. It just can't seem to map to my Java method with more than 1 parameter defined. At least, not until I figure out how to properly format them. :( — Miniversal

Colin Alworth Colin Alworth · Accepted Answer · 2019-03-01T21:44:22

In Javascript, unlike Java, you can actually pass a method as if it were a variable - you can reassign it, assign it to a variable, etc. That means that for JSNI references to work, we need to have a way not only to call them, but to reference them.

The standard JSNI pattern then is [email protected]::method(arg;types;)(actual, params)

In your case, this line

[email protected]::myMethod(Ljava/lang/String;Z);

should be changed to something like this

[email protected]::myMethod(Ljava/lang/String;Z)(s, b);

Please note however that Z refers to boolean, not Boolean, so the current code in your question is inconsistent. If only one method exists with a particular name, you can omit the types and just pass *:

[email protected]::myMethod(*)(s, b);

How to format param-signature for a JSNI method with more than 1 parameter?

2 Answers