Web3j directly gets string from contract by eth_call

Question

I just have a simple solidity contract:

pragma solidity ^0.4.19;

contract SampleContract {
    string value;

    function SampleContract() public {
        value = "hello world";
    }

    function getValue() public view returns (string){
        return value;
    }

    function setValue(string str) public {
        value = str;
    }
}

I am attempting to interact it with web3j. For now I have already deployed successfully and get the address.
I am trying to call method getValue() by codes:

static String call(String from, String contractAddress, String callData) throws Exception {
        Call call = new Call(from, contractAddress, callData);
        return service.ethCall(call, DefaultBlockParameter.valueOf("latest")).send().getValue();
    }

String callData = encodeGetValueFuncWithParams();
System.out.println(callData);
String result = call(from, contractAddress, callData);
System.out.println(result);    

I indeed get the result but in hex. The result I get is

0x
0000000000000000000000000000000000000000000000000000000000000020
000000000000000000000000000000000000000000000000000000000000000b
68656c6c6f20776f726c64000000000000000000000000000000000000000000

I converted this vaue and it is "hello world" but how can I directly get the value as string "hello world" instead of "0xxxxxxxx". The way I create my calldata is shown below:

static String encodeGetValueFuncWithParams(){
    Function function = new Function(
            "getValue",
            Collections.emptyList(),
            Arrays.asList(new TypeReference<DynamicBytes>(){})
    );
    String encodedFunc = FunctionEncoder.encode(function);
    return  encodedFunc;
}

My question is:
How do I construct my calldata so that I can directly get string value instead of hex value from contract.

Answer 1

See https://docs.web3j.io/transactions.html#querying-the-state-of-a-smart-contract. I think you need to call FunctionReturnDecoder.decode(). (You'll need to have available the list of output parameter types, so you'll need to restructure your code a bit.)