@Override
    protected IReadWriteStream<ApiRequest> getApiHandler(IPolicy policy, Object config) {
        if (policy instanceof IDataPolicy) {
            return ((IDataPolicy) policy).getRequestDataHandler(getHead(), getContext(), config);
        } else {
            return null;
        }
    }
@see io.apiman.gateway.engine.policy.Chain#getApiHandler(io.apiman.gateway.engine.policy.IPolicy, java.lang.Object)
gateway/engine/core/src/main/java/io/apiman/gateway/engine/policy/RequestChain.java