Encoding ABI function signature in Java using web3j?

Question

Is there a generic way to simply take an ABI function, something like:

{
   "name":"foo",
   "inputs":{
      "interalType":"uint256",
      "name":"bar",
      "type":"uint256"
   },
   "outputs":{
      "interalType":"uint256",
      "name":"baz",
      "type":"uint256"
   }
}

and have it encode the function signature in web3j? In web3js this seems to be incredibly simple, something like:

const eth = new Eth()
eth.abi.encodeFunctionSignature(myFunction)

Where myFunction is the section of the abi. Is there no way to do this in web3j? Or am I just missing something basic? I thought I might be able to do if I build up a Function object and then use the DefaultFunctionEncoder and then make a call to encodeFunction, but I don't see an easy way to do this on the fly. All examples I've see are using pre-built solidity contracts.

Is there a generic way to mimic what the javascript is doing?

Update:

I was able to 'mostly' do this by creating a horrible function containing a switch statement on the type and iterating through each potential type to generate a 'default version of the object. For instance return new Uint256(BigInteger.ZERO); sort of thing. It's hideous, and doesn't handle tuples (mostly because I haven't figured out how to handle those yet), but when I build my inputs that way for the function, when I encode it the value does match was web3js gives on that.

There 'has' to be a better way to handle this.

Update 2: Tuple types seem to be working now, but now I've discovered that working with byte32[] type, the signatures seem to differ from web3js and web3j. I'm having my object creator return Bytes32.DEFAULT as the Type in that case, but I'm not sure this is correct.

Answer 1

AFAIK, there is no way to accomplish what you're trying directly using web3j. However, what you can do is generate the contract wrappers, copy the generated Functions definitions. Then, encode/decode the calls as we are doing in the Encoder/Decoder tests.