Using ResponseEntity to extract information from another API

Question

I have 2 API lets call them API1 and API2
API1 is a system API that extracts data from a database and returns a List of Strings as a result.
API2 extracts the information from API1 and returns the List of Strings as is.

Now my question is if API1 is down how do I handle it. I know I have to use a ResponseEntity to extract the HTTP status code but I am unable to do it. Conside the code below as an example

API1 service

private static List<String> getData(int attribute1){
//A piece of code that extracts data from the database based on the attribute1 and store the information in a res object<br>
    return res;
}

API2 service

private static List<String> getData(int attribute1){
    String uri="localhost:9191/getData/"+attribute1;
    private RestTemplate restTemplate = new RestTemplate();
    List<String> res = restTemplate.getForObject(uri, List.class);
    return res;
}

Would I need to change my return type of API1 service functions
If so how would they look like
Irrespective of what happens in API1, API2 will change and how so to accomodate ResponseEntity
Any help would be much appreciated.

Enmanuel Rodríguez Paz · Accepted Answer · 2021-07-22 01:48:56Z

2

In case your API1 is down or has any problems, you'll get an exception calling the "getForObject" method using RestTemplate. If you read the documentation, you'll see that this method throws a RestClientException, which means that if you want to handle any problem with API1 you need to try/catch the method and handle the exception accordingly with your needs. So, you'll have something like this:

private static List getData(int attribute1) {

    String uri = "localhost:9191/getData/" + attribute1;

    private RestTemplate restTemplate = new RestTemplate();
    try {
        List res = restTemplate.getForObject(uri, List.class);
        return res;
    } catch(RestClientException rce) {
        // Here you'll handle the exception
    }
}

Also, note that the RestClientException has 3 direct subclasses: ResourceAccessException, RestClientResponseException and UnknownContentTypeException. You could catch each one of these instead of cathing RestClientException, so you can handle them in different ways.

answered Jul 22, 2021 at 1:48

Enmanuel Rodríguez Paz

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2 Comments

Ankit Kathait Over a year ago

Thanks for the answer Enmanuel. This looks more of a workaround. Do you also know how it can be handelled via ResponseEntity, as I was having touble to find an adequate source from the same. Also ResponseEntity has much more information, that I was hoping to further use.

Enmanuel Rodríguez Paz Over a year ago

The thing is that the class RestTemplate throws those 3 exceptions when you use the method getForObject, getForEntity, exchange, etc. RestTemplate has something called ResponseErrorHandler, which as the name suggests, handles the errors. By default, RestTemplate uses the implementation DefaultResponseErrorHandler which throws the exception when there's an HTTP response 4XX or 5XX. So, if you want to work the way you are trying, you need to implement your own ResponseErrorHandler. See this link to get some guide about it: baeldung.com/spring-rest-template-error-handling

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