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Handling of various exception cases in rest template call

I am making rest template call to get the data from other microservice for this I am using the exchange method. This I am doing when a particular function gets called and below is the sample code for the same.
#Service
public void findUserById()
{
String username = "chathuranga";
String password = "123";
Integer userId = 1;
String url = "http://localhost:8080/users/" + userId;
//setting up the HTTP Basic Authentication header value
String authorizationHeader = "Basic " + DatatypeConverter.printBase64Binary((username + ":" + password).getBytes());
HttpHeaders requestHeaders = new HttpHeaders();
//set up HTTP Basic Authentication Header
requestHeaders.add("Authorization", authorizationHeader);
requestHeaders.add("Accept", MediaType.APPLICATION_JSON_VALUE);
//request entity is created with request headers
HttpEntity<AddUserRequest> requestEntity = new HttpEntity<>(requestHeaders);
ResponseEntity<FindUserResponse> responseEntity = restTemplate.exchange(
url,
HttpMethod.GET,
requestEntity,
FindUserResponse.class
);
// if (responseEntity.getStatusCode() == HttpStatus.OK) {
// System.out.println("response received");
System.out.println(responseEntity.getBody());
//} else {
// System.out.println("error occurred");
// System.out.println(responseEntity.getStatusCode());
//}
}
To handle the various exceptions code for example 500, 404 I want to made resttemplate builder class, (not the commented code) Which must be coded in different class for this I am referring this (custom hadler part)
I am not using try catch as it is not good approach when multiple calls happen in production environment.
I am also getting resource access exception while using exchange function which also needs to handle.
Now I am not getting how this class of custom handler should be called for handling response like 500.
If someone can help me with the sample code that would be very helpfull as I cannot test my code because it is not deployed for testing purpose till now

here is a sample
#ControllerAdvice
public class ErrorHandler {
#ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR)
#ExceptionHandler(ResourceAccessException.class)
public #ResponseBody
String handleResourceAccessException(
ResourceAccessException ex) {
return "internal server error";
}
}
When you use #ControllerAdvice , it will catch the exception you mention in #ExceptionHandler and here you can handle it the way you want.
If you don't want to return the response to the client right away, (for example, ignore ResourceAccessException and continue), you can override the handleError method of DefaultResponseErrorHandler, which is used by RestTemplate to handle the non 2xx codes.
public class ErrorHandler extends DefaultResponseErrorHandler {
#Override
public void handleError(ClientHttpResponse response, HttpStatus statusCode) {
// write your code here
}
}

Is it possible to response with http error, that code are variable in java spring?

I have an Microservice and it gets an response from another. And based on the response I get I need to respond accordingly. I have no complete List of Error code I can receive, so the question is - can I generate error codes on the fly for my own response? From what I saw in spring the responses are predefined in code. I need to be flexible.
For example:
I receive a 409 I will respond with 409
I receive a 400 I will respond with 400
I receive a XXX code I will respond with XXX.

Try this code: (Sample code)
#RequestMapping(value = "/validate", method = RequestMethod.GET, produces = "application/json")
public ResponseEntity<ErrorBean> validateUser(#QueryParam("jsonInput") final String jsonInput) {
int numberHTTPDesired = 400;
ErrorBean responseBean = new ErrorBean();
responseBean.setError("ERROR");
responseBean.setMessage("Error in validation!");
return new ResponseEntity<ErrorBean>(responseBean, HttpStatus.valueOf(numberHTTPDesired));
}

I have worked on such a use case using the following concept. Try to create a generic exception across micro services. Take 2 params in the exception as error message and another one as error code. Throw the exception from the service being called and catch the same exception in the calling service in the rest template or feign client call.
public class MyException extends Exception {
private String errorCode;
public MyException() {
super();
}
public MyException(String message, String errorCode) {
super(message);
this.errorCode = errorCode;
}
}
--
try {
return myApiService.getUser();//call to myApiService microservice
} catch (MyException e) {
logger.error("Error: {}", e.getMessage());
throw new MyException(e.getMessage(), e.getCode());
}

How to throw exception based on feign.Response?

I have a Feign client with a method returning the feign.Response class. When another service throws an exception, feign puts an exception message on response body and puts status, but my service does not throw an exception. Can I throw an exception based on what I received in response like when I use ResponseEntity.
Feign client
#FeignClient(name = "ms-filestorage")
#RequestMapping(value = "/files", produces = "application/json")
public interface FileStorageApi {
#GetMapping(value = "/{id}")
Response getFileById(#PathVariable String id);
}
Usage of client
#Override
public Response getFileFromStorage(String fileId) {
Response fileStorageResponse = fileStorageApi.getFileById(fileId);
// NOW I USE THIS WAY FOR CHECKING RESPONSE BUT IT DOESN'T LOOK GOOD
//if (fileStorageResponse.status() != HttpStatus.OK.value()) {
// throw new OsagoServiceException();
//}
return fileStorageResponse;
}

Usually, if a Feign client call receives an error response from the API it is calling, it throws a FeignException.
This can be caught in a try / catch block (or a Feign ErrorDecoder if you want to be more sophisticated, but that's another post).
However, this is not the case if you map the error response into a Feign.Response return type - see this Github issue.
Instead of returning Feign.Response from getFileFromStorage(), you should create a custom Java object to hold the response, and you will then have access to the FeignException which you can handle as you wish.
Note that if you don't need access to the data that is returned from the API you are calling, changing the return type to void will also resolve this issue.

Testing Okhttp3 response body - java.lang.IllegalStateException: request == null

I have a method in class which does a HTTP GET call to get the response object and utilize this object further. The pesudo code is below:
public class ABC{
public method abc1(){
HttpUrl url = HttpUrl.parse("url").newBuilder()
.addPathSegment("path1")
.build();
Request request = new Request.Builder().url(url).build();
try (Response response = client.newCall(request).execute()) {
ResponseBody responseBody = response.body();
String body = responseBody.string();
//other logic
}catch (IOException e) {}
}
}
Now I am writing a unit test to test with different values in the response object (json object). This is as below:
public class ABCTest{
#Mock
private OkHttpClient mockHttpClient;
#Mock
private Call mockCall;
#Before
public void initMocks() {
MockitoAnnotations.initMocks(this);
}
#Test
public void abc1Test(){
ResponseObjectInJson responseObjectInJson = new ResponseObjectInJson(); //this is a object from my POJO class that i create in order to be received as a response
JSONObject jsonObject = new
JSONObject(responseObjectInJson);
ResponseBody body =
ResponseBody.create(MediaType.parse("application/json"),new
Gson().toJson(jsonObject));
Response.Builder builder = new Response.Builder();
builder.code(200);
Response response = builder.body(body).build();
when(mockCall.execute()).thenReturn(response);
when(mockHttpClient.newCall(any(Request.class))).thenReturn(mockCall);
//call the abc1() method here to see the response and behaviour
}
}
The problem is, when i debug, it throws InvocationTargetException when building the response builder.body(body).build();
And shows java.lang.IllegalStateException: request == null. I understand that i need to set request in the Response.Builder because when i evaluate the expression builder.body(body) in debugger, in the result it shows headers and body, but request is null.
i.e., builder.request(//a request here)
My question is:
1. In response why the request is needed?
2. How to set this? because i am unable to mock since its final.
Thanks in advance

HttpClientErrorException 400 null using RestTemplate in microServices

I have two microservices. The first one receives a call from the Frontend and then it calls to the second uService to receive some data. The last is returning an error response (Bad Request, this is ok - it is a use-case). However, I am losing the body (message) returned from the second microservice, as the first is throwing a HttpClientErrorException 400 null in the call
This is my code:
ResponseEntity<MyEntity> entityResponse = restTemplate.getForEntity(url, MyEntity.class, id);
I am not able to do entityResponse.getStatusCode() as an exception is thrown.
Handled it in the ControllerAdvice, my exception message is "400 null" even I return a custom message from the service.
So, I would like to get the response message sent in the called uservice to manage it.
Thanks in advance.

The answers here that explain how to catch the exception and access the body are correct. However, you may use a different approach. You can use a 3-d party library that sends Http request and handles the response. One of the well-known products would be Apache commons HTTPClient: HttpClient javadoc, HttpClient Maven artifact. There is by far less known but much simpler HTTPClient (part of an open source MgntUtils library written by me): MgntUtils HttpClient javadoc, MgntUtils maven artifact, MgntUtils Github. Using either of those libraries you can send your REST request and receive response independently from Spring as part of your business logic

What I'm doing in my project is the following.
MicroService_2 calls MicroService_1.
MicroService_1
MicroService_1 returns for example a HTTP 404 exception if the entity isn't found.
#RestController
#RequestMapping(value = "/api/v1/")
public class Service1Controller {
#RequestMapping(value = "/{id}", method = RequestMethod.GET)
public #ResponseBody MyEntity getMyEntity(#PathVariable String id) throws NotFoundException {
MyEntity result = ...
if(result == null) {
throw new NotFoundException("MyEntity [id: "+id+"] not found");
}
return result;
}
#ControllerAdvice
public class RestEndpointExceptionHandler extends RestExceptionHandler {
#ExceptionHandler(NotFoundException.class)
public ResponseEntity<String> handleNotFoundException(HttpServletRequest req, NotFoundException ex) throws NotFoundException {
return new ResponseEntity<String>(ex.getMessage(), HttpStatus.NOT_FOUND);
}
}
}
MicroService_2
The MicroService_2 calls MicroService_1 and catches the exception by HTTP code and regenerate the NotFoundException.
#Override
public MyEntity getMyEntity(Principal principal) {
try {
ResponseEntity<MyEntity> entityResponse = restTemplate.getForEntity(url, MyEntity.class, id);
return entityResponse.getBody();
} catch(HttpClientErrorException e) {
HttpStatus status = e.getStatusCode();
if (status == HttpStatus.NOT_FOUND) {
throw new NotFoundException(e.getResponseBodyAsString()); // should be "MyEntity [id: {id}] not found"
} else {
throw new UnexpectedServerException(e.getResponseBodyAsString());
}
}
}

The Spring RestTemplate throws an error in case of 500 or 400 status codes. So if your second service responds with an error an exception will be thrown by the RestTemplate call in your first service.
HttpClientErrorException: in case of HTTP status 4xx
HttpServerErrorException: in case of HTTP status 5xx
UnknownHttpStatusCodeException: in case of an unknown HTTP status
To get the response message you could either catch the exception. E.g:
try {
ResponseEntity<MyEntity> entityResponse = restTemplate.getForEntity(url, MyEntity.class, id);
} catch(HttpStatusCodeException e) {
// e.getResponseBodyAsString();
}
or define a ResponseErrorHandler. The ResponseErrorHandler can be set during the instantiation of the RestTemplate. In the handleError method you will also be able to access the response message.
#Override
public void handleError(ClientHttpResponse httpResponse)
throws IOException {
}