Q: How to capture error responses from Rest Template in spring boot? I've 2 springboot REST APIs REST-A & REST-B. REST-B is interacting with mongodb for CRUD operations. And REST-A is calling REST-B endpoints for different reasons.
Controller in REST-B (Customer API)
public class CustomerController {
    
    @Autowired
    private CustomerRepository customerRepository;
    
    @GetMapping(value = "/customers/{id}")
    public ResponseEntity<Customer> getCustomerByExternalReferenceId(@PathVariable(value = "id") String id)
            throws ResourceNotFoundException {
        System.out.println("Customer id received :: " + id);
        Customer customer = customerRepository.findByExternalCustomerReferenceId(id)
                .orElseThrow(() -> new ResourceNotFoundException("Customer not found for this id :: " + id));
        return ResponseEntity.ok().body(customer);
    }
}

This endpoint works fine if I call from postman for both if customer found in DB and if customer not found in DB.


Now, if I try to call the same endpoint from REST-A and if customer found in DB I can get the response.
        String url = "http://localhost:8086/customer-api/customers/{id}";
        String extCustRefId = 
        setupRequest.getPayload().getCustomer().getCustomerReferenceId();
        
        // URI (URL) parameters
        Map<String, String> urlParams = new HashMap<>();
        urlParams.put("id", extCustRefId); // here I tried with id that exists in DB and getting 200 ok response
        
        HttpHeaders headers = new HttpHeaders();
        headers.set("X-GP-Request-Id", "abc-xyz-123");
        headers.set("Content-Type", "application/json");
        headers.set("Accept", "application/json");
        headers.set("Content-Length", "65");
        
        String searchurl = UriComponentsBuilder.fromUriString(url).buildAndExpand(urlParams).toString();
        
        System.out.println(searchurl);
        
        HttpEntity request = new HttpEntity(headers);
        RestTemplate restTemplate = new RestTemplate();
        try {
            ResponseEntity<String> response = restTemplate.exchange(
                    searchurl,
                    HttpMethod.GET,
                    request,
                    String.class
            );
        } catch (Exception e) {
            e.printStackTrace();
        }

But if there's no customer found from REST-B (Customer API) then I'm getting
http://localhost:8086/customer-api/customers/customer-528f2331-d0c8-46f6-88c2-7445ee6f4821
Customer id received :: customer-528f2331-d0c8-46f6-88c2-7445ee6f4821
org.springframework.web.client.HttpClientErrorException: 404 null
        at org.springframework.web.client.DefaultResponseErrorHandler.handleError(DefaultResponseErrorHandler.java:78)
        at org.springframework.web.client.RestTemplate.handleResponse(RestTemplate.java:700)
        at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:653)
        at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:613)
        at org.springframework.web.client.RestTemplate.exchange(RestTemplate.java:531)

How do I call rest endpoint from one springboot application to another and handle response properly?

A: You can get the response body from HttpClientErrorException as follows:
try {
    ResponseEntity<String> response = restTemplate.exchange(
            searchurl,
            HttpMethod.GET,
            request,
            String.class
    );
} catch (HttpClientErrorException e) {
    String errorResponseBody = e.getResponseBodyAsString();
    e.printStackTrace();
}

You can then use Jackson ObjectMapper to map the String to a Java object.
