Using ParameterizedTypeReference to setExpectedResponseType for HttpRequestExecutingMessageHandler

Question

I'm trying to configure a gateway using the HttpRequestExecutingMessageHandler . The problem that I'm facing is to setExpectedResponseType to a generic type.

I have found some solutions when you use the RestTemplate directly, but when dealing with the configuration through the HttpRequestExecutingMessageHandler I haven't been able to make it call the proper exchange method of the RestTemplate that receives the ParameterizedTypeReference .

This is the example code:

My generic class:

   public class ListWrapperModel<T> {

   public ListWrapperModel() {}
   private List<T> list;
}

My configuration for HttpRequestExecutingMessageHandler:

    Map<String, Expression> uriVariableExp = getDefaultEndpointProperties();
    SpelExpressionParser parser = new SpelExpressionParser();
    uriVariableExp.put("id", parser.parseExpression("payload"));

    String endpoint = "{host}/models?id={id}";
    HttpRequestExecutingMessageHandler gateway;

    gateway = new HttpRequestExecutingMessageHandler(endpoint, getRestTemplate());
    gateway.setRequiresReply(true);
    gateway.setHttpMethod(HttpMethod.GET);
    gateway.setExpectedResponseType(new ParameterizedTypeReference<ListWrapperModel<Model>>(){}.getClass());
    gateway.setUriVariableExpressions(uriVariableExp);

    return gateway;

This is one of the scenarios that I've tried, the other one, was doing this:

gateway.setExpectedResponseType(new ParameterizedTypeReference<ListWrapperModel<Model>>(){}.getType().getClass());

But didn't work.

Debugging HttpRequestExecutingMessageHandler, I notice that when it is trying to determinate the expected type, the return type is: com.host.app.service.gateway.http.ServiceConfiguration$1

I'm new to java but I will assume that the $1 is the anonymous type created.

I would like to ask if there is a way to configure this so that can work properly.

Thanks!

Answer 1

I managed to solve the problem by using a response type value expression. The following settings worked for me:

ParameterizedTypeReference<ListWrapperModel<Model>> type = new ParameterizedTypeReference<ListWrapperModel<Model>>() { };
gateway.setExpectedResponseTypeExpression(new ValueExpression<>(type));

The value expression will later be evaluated to the provided ParameterizedTypeReference which the underlying RestTemplate will use to convert the result.