How to handle RestTemplate Exceptions in a client?

I have a springboot application which invokes a Client Library I've written, to make REST calls to a third party service.

I want to be able to catch any/all exceptions which may come from this client library, and map them to my own custom exception, which I can catch in my application.

Within the Client Library, I have a RestTemplate bean, and I've bound a ErrorHandler to it, like so:

public class CustomRestTemplateErrorHandler implements ResponseErrorHandler {

}

I use the typical methods of 'hasError' and 'handleError'. If I return a HTTP400 with some expected error response body, I can catch this error and map it to my exception, as shown here:

@Override
    public void handleError(ClientHttpResponse response) {
        try {
            if (!response.getStatusCode().is2xxSuccessful()) {
                BufferedReader reader = new BufferedReader(
                        new InputStreamReader(response.getBody()));
                String httpBodyResponse = reader.lines()
                        .collect(Collectors.joining(""));

                ObjectMapper mapper = new ObjectMapper();
                ExpectedErrorResponse errorResponse = mapper.readValue(httpBodyResponse, ExpectedErrorResponse.class);
                throw new CustomException(response.getStatusCode(), errorResponse);
            }
        } catch (IOException ioException) {
            throw new CustomException(ioException.getMessage(), ioException.getCause());
        }
    }

Lets say I run this test, and the downstream server isn't running. I'll get the following Exception, which isn't caught by my error handler: Caused by: org.springframework.web.client.ResourceAccessException: I/O error on POST request for "http://127.0.0.1:8082/": Connect to 127.0.0.1:8082 [/127.0.0.1] failed: Connection refused: connect; nested exception is org.apache.http.conn.HttpHostConnectException: Connect to 127.0.0.1:8082 [/127.0.0.1] failed: Connection refused: connect

How do I catch both the expected type of error response, and a RestClientException, within the ResponseErrorHandler?

Thanks

Problem statement

ResourceAccessException is an exception class which is not inherited from IOException, so your catch will not be entered in this specific case. So, you have several options:

Catch Exception

Code:

catch (Exception exception) {
    //your code
}

this would handle both IOException and RestClientException. Even though this is a short and easy-to-read solution, if you may have other exceptions to catch in a different manner, then you may want to decide against it. But in many cases this could help you. Ultimately it is you who needs to decide whether this is the way to go.

Catch multiple exceptions

Code

catch (IOException ioException) {
    // Your code
} catch (RestClientException restClientException) {
    // Your code
}

This is precisely doing what you want, so it is a useful solution if the first suggestion does not help.

Catch multiple exception types in the same block

Code

catch (IOException | RestClientException myException) {
    // Your code
}

This is whitelisting the root exception types you want to handle and it's a neat way to approach the problem.