Spring Resttemplate exception handling

Below is the code snippet; basically, I am trying to propagate the exception when the error code is anything other than 200.

ResponseEntity<Object> response = restTemplate.exchange(url.toString().replace("{version}", version),
					HttpMethod.POST, entity, Object.class);
			if(response.getStatusCode().value()!= 200){
				logger.debug("Encountered Error while Calling API");
				throw new ApplicationException();
			}

However in the case of a 500 response from the server I am getting the exception

org.springframework.web.client.HttpServerErrorException: 500 Internal Server Error
	at org.springframework.web.client.DefaultResponseErrorHandler.handleError(DefaultResponseErrorHandler.java:94) ~[spring-web-4.2.3.RELEASE.jar:4.2.3.RELEASE]

Do I really need to wrap the rest template exchange method in try? What would then be the purpose of codes?

You want to create a class that implements ResponseErrorHandler and then use an instance of it to set the error handling of your rest template:

public class MyErrorHandler implements ResponseErrorHandler {
  @Override
  public void handleError(ClientHttpResponse response) throws IOException {
    // your error handling here
  }

  @Override
  public boolean hasError(ClientHttpResponse response) throws IOException {
     ...
  }
}

[...]

public static void main(String args[]) {
  RestTemplate restTemplate = new RestTemplate();
  restTemplate.setErrorHandler(new MyErrorHandler());
}

Also, Spring has the class DefaultResponseErrorHandler, which you can extend instead of implementing the interface, in case you only want to override the handleError method.

public class MyErrorHandler extends DefaultResponseErrorHandler {
  @Override
  public void handleError(ClientHttpResponse response) throws IOException {
    // your error handling here
  }
}

Take a look at its source code to have an idea of how Spring handles HTTP errors.

Spring cleverly treats http error codes as exceptions, and assumes that your exception handling code has the context to handle the error. To get exchange to function as you would expect it, do this:

    try {
        return restTemplate.exchange(url, httpMethod, httpEntity, String.class);
    } catch(HttpStatusCodeException e) {
        return ResponseEntity.status(e.getRawStatusCode()).headers(e.getResponseHeaders())
                .body(e.getResponseBodyAsString());
    }

This will return all the expected results from the response.

You should catch a HttpStatusCodeException exception:

try {
    restTemplate.exchange(...);
} catch (HttpStatusCodeException exception) {
    int statusCode = exception.getStatusCode().value();
    ...
}

Another solution is the one described here at the end of this post by "enlian": http://springinpractice.com/2013/10/07/handling-json-error-object-responses-with-springs-resttemplate

try{
     restTemplate.exchange(...)
} catch(HttpStatusCodeException e){
     String errorpayload = e.getResponseBodyAsString();
     //do whatever you want
} catch(RestClientException e){
     //no response payload, tell the user sth else 
}

Spring abstracts you from the very very very large list of http status code. That is the idea of the exceptions. Take a look into org.springframework.web.client.RestClientException hierarchy:

You have a bunch of classes to map the most common situations when dealing with http responses. The http codes list is really large, you won't want write code to handle each situation. But for example, take a look into the HttpClientErrorException sub-hierarchy. You have a single exception to map any 4xx kind of error. If you need to go deep, then you can. But with just catching HttpClientErrorException, you can handle any situation where bad data was provided to the service.

The DefaultResponseErrorHandler is really simple and solid. If the response status code is not from the family of 2xx, it just returns true for the hasError method.

I have handled this as below:

try {
  response = restTemplate.postForEntity(requestUrl, new HttpEntity<>(requestBody, headers), String.class);
} catch (HttpStatusCodeException ex) {
  response = new ResponseEntity<String>(ex.getResponseBodyAsString(), ex.getResponseHeaders(), ex.getStatusCode());
}

A very simple solution can be:

try {
     requestEntity = RequestEntity
     .get(new URI("user String"));
    
    return restTemplate.exchange(requestEntity, String.class);
} catch (RestClientResponseException e) {
    	return ResponseEntity.status(e.getRawStatusCode()).body(e.getResponseBodyAsString());
}

If you use pooling (http client factory) or load balancing (eureka) mechanism with your RestTemplate, you will not have the luxury of creating a new RestTemplate per class. If you are calling more than one service you cannot use setErrorHandler because if would be globally used for all your requests.

In this case, catching the HttpStatusCodeException seems to be the better option.

The only other option you have is to define multiple RestTemplate instances using the @Qualifier annotation.

Also - but this is my own taste - I like my error handling snuggled tightly to my calls.

The code of exchange is below:

public <T> ResponseEntity<T> exchange(String url, HttpMethod method,
			HttpEntity<?> requestEntity, Class<T> responseType, Object... uriVariables) throws RestClientException

Exception RestClientException has HttpClientErrorException and HttpStatusCodeException exception.

So in RestTemplete there may occure HttpClientErrorException and HttpStatusCodeException exception. In exception object you can get exact error message using this way: exception.getResponseBodyAsString()

Here is the example code:

public Object callToRestService(HttpMethod httpMethod, String url, Object requestObject, Class<?> responseObject) {

        printLog( "Url : " + url);
        printLog( "callToRestService Request : " + new GsonBuilder().setPrettyPrinting().create().toJson(requestObject));

        try {

            RestTemplate restTemplate = new RestTemplate();
            restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
            restTemplate.getMessageConverters().add(new StringHttpMessageConverter());


            HttpHeaders requestHeaders = new HttpHeaders();
            requestHeaders.setContentType(MediaType.APPLICATION_JSON);

            HttpEntity<Object> entity = new HttpEntity<>(requestObject, requestHeaders);

            long start = System.currentTimeMillis();

            ResponseEntity<?> responseEntity = restTemplate.exchange(url, httpMethod, entity, responseObject);

            printLog( "callToRestService Status : " + responseEntity.getStatusCodeValue());


            printLog( "callToRestService Body : " + new GsonBuilder().setPrettyPrinting().create().toJson(responseEntity.getBody()));

            long elapsedTime = System.currentTimeMillis() - start;
            printLog( "callToRestService Execution time: " + elapsedTime + " Milliseconds)");

            if (responseEntity.getStatusCodeValue() == 200 && responseEntity.getBody() != null) {
                return responseEntity.getBody();
            }

        } catch (HttpClientErrorException exception) {
            printLog( "callToRestService Error :" + exception.getResponseBodyAsString());
            //Handle exception here
        }catch (HttpStatusCodeException exception) {
            printLog( "callToRestService Error :" + exception.getResponseBodyAsString());
            //Handle exception here
        }
        return null;
    }

Here is the code description:

In this method you have to pass request and response class. This method will automatically parse response as requested object.

First of All you have to add message converter.

restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
            restTemplate.getMessageConverters().add(new StringHttpMessageConverter());

Then you have to add requestHeader. Here is the code:

HttpHeaders requestHeaders = new HttpHeaders();
            requestHeaders.setContentType(MediaType.APPLICATION_JSON);

            HttpEntity<Object> entity = new HttpEntity<>(requestObject, requestHeaders);

Finally, you have to call exchange method:

ResponseEntity<?> responseEntity = restTemplate.exchange(url, httpMethod, entity, responseObject);

For prety printing i used Gson library. here is the gradle : compile 'com.google.code.gson:gson:2.4'

You can just call the bellow code to get response:

ResponseObject response=new RestExample().callToRestService(HttpMethod.POST,"URL_HERE",new RequestObject(),ResponseObject.class);

Here is the full working code:

import com.google.gson.GsonBuilder;
import org.springframework.http.*;
import org.springframework.http.converter.StringHttpMessageConverter;
import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter;
import org.springframework.web.client.HttpClientErrorException;
import org.springframework.web.client.HttpStatusCodeException;
import org.springframework.web.client.RestTemplate;


public class RestExample {

    public RestExample() {
        
    }

    public Object callToRestService(HttpMethod httpMethod, String url, Object requestObject, Class<?> responseObject) {

        printLog( "Url : " + url);
        printLog( "callToRestService Request : " + new GsonBuilder().setPrettyPrinting().create().toJson(requestObject));

        try {

            RestTemplate restTemplate = new RestTemplate();
            restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
            restTemplate.getMessageConverters().add(new StringHttpMessageConverter());


            HttpHeaders requestHeaders = new HttpHeaders();
            requestHeaders.setContentType(MediaType.APPLICATION_JSON);

            HttpEntity<Object> entity = new HttpEntity<>(requestObject, requestHeaders);

            long start = System.currentTimeMillis();

            ResponseEntity<?> responseEntity = restTemplate.exchange(url, httpMethod, entity, responseObject);

            printLog( "callToRestService Status : " + responseEntity.getStatusCodeValue());


            printLog( "callToRestService Body : " + new GsonBuilder().setPrettyPrinting().create().toJson(responseEntity.getBody()));

            long elapsedTime = System.currentTimeMillis() - start;
            printLog( "callToRestService Execution time: " + elapsedTime + " Milliseconds)");

            if (responseEntity.getStatusCodeValue() == 200 && responseEntity.getBody() != null) {
                return responseEntity.getBody();
            }

        } catch (HttpClientErrorException exception) {
            printLog( "callToRestService Error :" + exception.getResponseBodyAsString());
            //Handle exception here
        }catch (HttpStatusCodeException exception) {
            printLog( "callToRestService Error :" + exception.getResponseBodyAsString());
            //Handle exception here
        }
        return null;
    }
    
    private void printLog(String message){
        System.out.println(message);
    }
}

Thanks :)

To extedend @carcaret answer a bit....

Consider your response errors are returned by json message. For example the API may return 204 as status code error and a json message as error list. In this case you need to define which messages should spring consider as error and how to consume them.

As a sample your API may return some thing like this, if error happens:

 { "errorCode":"TSC100" , "errorMessage":"The foo bar error happend" , "requestTime" : "202112827733" .... } 

To consume above json and throw a custom exception, you can do as below:

First define a class for mapping error ro object

//just to map the json to object
public class ServiceErrorResponse implements Serializable {

	//setter and getters
	private Object errorMessage;
    private String errorCode;
    private String requestTime;
   
}

Now define the error handler:

public class ServiceResponseErrorHandler implements ResponseErrorHandler {

    private List<HttpMessageConverter<?>> messageConverters;

    @Override
    public boolean hasError(ClientHttpResponse response) throws IOException {
        
        return (response.getStatusCode().is4xxClientError() ||
                response.getStatusCode().is5xxServerError());
    }

    @Override
    public void handleError(ClientHttpResponse response) throws IOException {
    	
        @SuppressWarnings({ "unchecked", "rawtypes" })
		HttpMessageConverterExtractor<ServiceErrorResponse> errorMessageExtractor = 
        		new HttpMessageConverterExtractor(ServiceErrorResponse.class, messageConverters);
        
        ServiceErrorResponse errorObject = errorMessageExtractor.extractData(response);
        
       throw new ResponseEntityErrorException(
    		   ResponseEntity.status(response.getRawStatusCode())
    		   					.headers(response.getHeaders())
    		   					.body(errorObject)
    		   );
        
    }

    public void setMessageConverters(List<HttpMessageConverter<?>> messageConverters) {
        this.messageConverters = messageConverters;
    }
}

The custom Exception will be:

public class ResponseEntityErrorException extends RuntimeException  {
	
    private ResponseEntity<ServiceErrorResponse> serviceErrorResponseResponse;

    public ResponseEntityErrorException(ResponseEntity<ServiceErrorResponse> serviceErrorResponseResponse) {
        this.serviceErrorResponseResponse = serviceErrorResponseResponse;
    }
    
    public ResponseEntity<ServiceErrorResponse> getServiceErrorResponseResponse() {
        return serviceErrorResponseResponse;
    }
}

To use it:

RestTemplateResponseErrorHandler errorHandler = new 
RestTemplateResponseErrorHandler();
//pass the messageConverters to errror handler and let it convert json to object
        errorHandler.setMessageConverters(restTemplate.getMessageConverters());
        restTemplate.setErrorHandler(errorHandler);

This is how to handle exceptions in Rest Template

        try {
        return restTemplate.exchange("URL", HttpMethod.POST, entity, String.class);
            }
        catch (HttpStatusCodeException e) 
        {
        return ResponseEntity.status(e.getRawStatusCode()).headers(e.getResponseHeaders())
                .body(e.getResponseBodyAsString());
        }

Here is my POST method with HTTPS which returns a response body for any type of bad responses.

public String postHTTPSRequest(String url,String requestJson)
{
    //SSL Context
    CloseableHttpClient httpClient = HttpClients.custom().setSSLHostnameVerifier(new NoopHostnameVerifier()).build();
    HttpComponentsClientHttpRequestFactory requestFactory = new HttpComponentsClientHttpRequestFactory();
    requestFactory.setHttpClient(httpClient);
    //Initiate REST Template
    RestTemplate restTemplate = new RestTemplate(requestFactory);
    HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.APPLICATION_JSON);
    //Send the Request and get the response.
    HttpEntity<String> entity = new HttpEntity<String>(requestJson,headers);
    ResponseEntity<String> response;
    String stringResponse = "";
    try {
        response = restTemplate.postForEntity(url, entity, String.class);
        stringResponse = response.getBody();
    }
    catch (HttpClientErrorException e)
    {
        stringResponse = e.getResponseBodyAsString();
    }
    return stringResponse;
}

I fixed it by overriding the hasError method from DefaultResponseErrorHandler class:

public class BadRequestSafeRestTemplateErrorHandler extends DefaultResponseErrorHandler
{
	@Override
	protected boolean hasError(HttpStatus statusCode)
	{
		if(statusCode == HttpStatus.BAD_REQUEST)
		{
			return false;
		}
		return statusCode.isError();
	}
}

And you need to set this handler for restemplate bean:

@Bean
	protected RestTemplate restTemplate(RestTemplateBuilder builder)
	{
		return builder.errorHandler(new BadRequestSafeRestTemplateErrorHandler()).build();
	}

Try using @ControllerAdvice. This allows you to handle the exception only once and have all 'custom' handled exceptions in one place.

https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/web/bind/annotation/ControllerAdvice.html

example

@ControllerAdvice
public class MyExceptionHandler extends ResponseEntityExceptionHandler{

    @ExceptionHandler(MyException.class)
    protected ResponseEntity<Object> handleMyException(){
      MyException exception,
      WebRequest webRequest) {
    return handleExceptionInternal(
        exception,
        exception.getMessage(),
        exception.getResponseHeaders(),
        exception.getStatusCode(),
        webRequest);
}

Read about global exception handling in global exception handler add the below method. this will work.

@ExceptionHandler( {HttpClientErrorException.class, HttpStatusCodeException.class, HttpServerErrorException.class})
@ResponseBody
public ResponseEntity<Object> httpClientErrorException(HttpStatusCodeException e) throws IOException {
    BodyBuilder bodyBuilder = ResponseEntity.status(e.getRawStatusCode()).header("X-Backend-Status", String.valueOf(e.getRawStatusCode()));
    if (e.getResponseHeaders().getContentType() != null) {
        bodyBuilder.contentType(e.getResponseHeaders().getContentType());
    }
    return bodyBuilder.body(e.getResponseBodyAsString());
}