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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
}
}

Sending request body in GET method not working

Im currently in a task in which i have to send a GET request with a body. Im a aware this isn't a good practice and that i should send the json through query params.
But I'm bound to do it like this.
So let's continue. I use RestTemplate with exchange but due to SimpleClientHttpRequestFactory implementation i cannot send a body with a GET method.
RestTemplate template = new RestTemplate(new CustomClientHttpRequestFactory());
httpHeaders.setContentType(APPLICATION_JSON);
httpHeaders.set("token", token.getToken());
httpHeaders.set("companyId", companyId);
URI uri = new URI(getInspectionsUrl);
HttpEntity<InspectionsInputDTO> entity = new HttpEntity<InspectionsInputDTO>(inputDTO, httpHeaders);
response = template.exchange(uri, GET, entity, InspectionsResponseDTO.class);
After some research i found the following code:
class CustomClientHttpRequestFactory extends SimpleClientHttpRequestFactory {
#Override
protected void prepareConnection(HttpURLConnection connection, String httpMethod) throws IOException {
super.prepareConnection(connection, httpMethod);
if ("GET".equals(httpMethod)) {
connection.setDoOutput(true);
}
}
}
// RestTemplate initialization
RestTemplate template = new RestTemplate(new CustomClientHttpRequestFactory());
This tries to override SimpleClientHttpRequestFactory httpMethod allowance but id does not work. The question is, how can i send a Request BODY in GET request with RestTemplate. Maybe there is another way to override SimpleClientHttpRequestFactory. Im new in this strange world of spring, sorry if im saying something wrong (:

Why RestTemplate GET response is in JSON when should be in XML?

I struggled with an extrange spring behavior using RestTemplate (org.springframework.web.client.RestTemplate) without success.
I use in my hole application below code and always receive an XML response, which I parse and evaluate its result.
String apiResponse = getRestTemplate().postForObject(url, body, String.class);
But can't figure out why a server response is in JSON format after executing:
String apiResponse = getRestTemplate().getForObject(url, String.class);
I've debugged at low level RestTemplate and the content type is XML, but have no idea why the result is in JSON.
When I access from a browser the response is also in XML, but in apiResponse I got JSON.
I tried many options after reading Spring documentation
http://docs.spring.io/spring/docs/3.0.x/api/org/springframework/web/client/RestTemplate.html
Also tried to modify explicitly the headers but still can't figure it out.
I debugged RestTemplate class and noticed that this method is always setting application/json:
public void doWithRequest(ClientHttpRequest request) throws IOException {
if (responseType != null) {
List<MediaType> allSupportedMediaTypes = new ArrayList<MediaType>();
for (HttpMessageConverter<?> messageConverter : getMessageConverters()) {
if (messageConverter.canRead(responseType, null)) {
List<MediaType> supportedMediaTypes = messageConverter.getSupportedMediaTypes();
for (MediaType supportedMediaType : supportedMediaTypes) {
if (supportedMediaType.getCharSet() != null) {
supportedMediaType =
new MediaType(supportedMediaType.getType(), supportedMediaType.getSubtype());
}
allSupportedMediaTypes.add(supportedMediaType);
}
}
}
if (!allSupportedMediaTypes.isEmpty()) {
MediaType.sortBySpecificity(allSupportedMediaTypes);
if (logger.isDebugEnabled()) {
logger.debug("Setting request Accept header to " + allSupportedMediaTypes);
}
request.getHeaders().setAccept(allSupportedMediaTypes);
}
}
}
Could you give an idea?

I could solve my issue with RC.'s help. I'll post the answer to help other people.
The problem was that Accept header is automatically set to APPLICATION/JSON so I had to change the way to invoke the service in order to provide the Accept header I want.
I changed this:
String response = getRestTemplate().getForObject(url, String.class);
To this in order to make the application work:
// Set XML content type explicitly to force response in XML (If not spring gets response in JSON)
HttpHeaders headers = new HttpHeaders();
headers.setAccept(Arrays.asList(MediaType.APPLICATION_XML));
HttpEntity<String> entity = new HttpEntity<String>("parameters", headers);
ResponseEntity<String> response = getRestTemplate().exchange(url, HttpMethod.GET, entity, String.class);
String responseBody = response.getBody();

Sending GET request with Authentication headers using restTemplate

I need to retrieve resources from my server by sending a GET request with some Authorization headers using RestTemplate.
After going over the docs I noticed that none of the GET methods accepts headers as a parameter, and the only way to send Headers such as accept and Authorization is by using the exchange method.
Since it is a very basic action I am wondering if I am missing something and there another, easier way to do it?

You're not missing anything. RestTemplate#exchange(..) is the appropriate method to use to set request headers.
Here's an example (with POST, but just change that to GET and use the entity you want).
Here's another example.
Note that with a GET, your request entity doesn't have to contain anything (unless your API expects it, but that would go against the HTTP spec). It can be an empty String.

You can use postForObject with an HttpEntity. It would look like this:
HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_JSON);
headers.set("Authorization", "Bearer "+accessToken);
HttpEntity<String> entity = new HttpEntity<String>(requestJson,headers);
String result = restTemplate.postForObject(url, entity, String.class);
In a GET request, you'd usually not send a body (it's allowed, but it doesn't serve any purpose). The way to add headers without wiring the RestTemplate differently is to use the exchange or execute methods directly. The get shorthands don't support header modification.
The asymmetry is a bit weird on a first glance, perhaps this is going to be fixed in future versions of Spring.

Here's a super-simple example with basic authentication, headers, and exception handling...
private HttpHeaders createHttpHeaders(String user, String password)
{
String notEncoded = user + ":" + password;
String encodedAuth = "Basic " + Base64.getEncoder().encodeToString(notEncoded.getBytes());
HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_JSON);
headers.add("Authorization", encodedAuth);
return headers;
}
private void doYourThing()
{
String theUrl = "http://blah.blah.com:8080/rest/api/blah";
RestTemplate restTemplate = new RestTemplate();
try {
HttpHeaders headers = createHttpHeaders("fred","1234");
HttpEntity<String> entity = new HttpEntity<String>("parameters", headers);
ResponseEntity<String> response = restTemplate.exchange(theUrl, HttpMethod.GET, entity, String.class);
System.out.println("Result - status ("+ response.getStatusCode() + ") has body: " + response.hasBody());
}
catch (Exception eek) {
System.out.println("** Exception: "+ eek.getMessage());
}
}

These days something like the following will suffice:
HttpHeaders headers = new HttpHeaders();
headers.setBearerAuth(accessToken);
restTemplate.exchange(RequestEntity.get(new URI(url)).headers(headers).build(), returnType);

All of these answers appear to be incomplete and/or kludges. Looking at the RestTemplate interface, it sure looks like it is intended to have a ClientHttpRequestFactory injected into it, and then that requestFactory will be used to create the request, including any customizations of headers, body, and request params.
You either need a universal ClientHttpRequestFactory to inject into a single shared RestTemplate or else you need to get a new template instance via new RestTemplate(myHttpRequestFactory).
Unfortunately, it looks somewhat non-trivial to create such a factory, even when you just want to set a single Authorization header, which is pretty frustrating considering what a common requirement that likely is, but at least it allows easy use if, for example, your Authorization header can be created from data contained in a Spring-Security Authorization object, then you can create a factory that sets the outgoing AuthorizationHeader on every request by doing SecurityContextHolder.getContext().getAuthorization() and then populating the header, with null checks as appropriate. Now all outbound rest calls made with that RestTemplate will have the correct Authorization header.
Without more emphasis placed on the HttpClientFactory mechanism, providing simple-to-overload base classes for common cases like adding a single header to requests, most of the nice convenience methods of RestTemplate end up being a waste of time, since they can only rarely be used.
I'd like to see something simple like this made available
#Configuration
public class MyConfig {
#Bean
public RestTemplate getRestTemplate() {
return new RestTemplate(new AbstractHeaderRewritingHttpClientFactory() {
#Override
public HttpHeaders modifyHeaders(HttpHeaders headers) {
headers.addHeader("Authorization", computeAuthString());
return headers;
}
public String computeAuthString() {
// do something better than this, but you get the idea
return SecurityContextHolder.getContext().getAuthorization().getCredential();
}
});
}
}
At the moment, the interface of the available ClientHttpRequestFactory's are harder to interact with than that. Even better would be an abstract wrapper for existing factory implementations which makes them look like a simpler object like AbstractHeaderRewritingRequestFactory for the purposes of replacing just that one piece of functionality. Right now, they are very general purpose such that even writing those wrappers is a complex piece of research.

A simple solution would be to configure static http headers needed for all calls in the bean configuration of the RestTemplate:
#Configuration
public class RestTemplateConfig {
#Bean
public RestTemplate getRestTemplate(#Value("${did-service.bearer-token}") String bearerToken) {
RestTemplate restTemplate = new RestTemplate();
restTemplate.getInterceptors().add((request, body, clientHttpRequestExecution) -> {
HttpHeaders headers = request.getHeaders();
if (!headers.containsKey("Authorization")) {
String token = bearerToken.toLowerCase().startsWith("bearer") ? bearerToken : "Bearer " + bearerToken;
request.getHeaders().add("Authorization", token);
}
return clientHttpRequestExecution.execute(request, body);
});
return restTemplate;
}
}

Using Spring MVC, accepting POST requests with bad JSON leads to a default 400 error code server page being returned

I am working on a REST api. Receiving a POST message with bad JSON (e.g. { sdfasdfasdf } ) causes Spring to return the default server page for a 400 Bad Request Error. I do not want to return a page, I want to return a custom JSON Error object.
I can do this when there is an exception thrown by using an #ExceptionHandler. So if it is a blank request or a blank JSON object (e.g. { } ), it will throw a NullPointerException and I can catch it with my ExceptionHandler and do whatever I please.
The problem then, is that Spring doesn't actually throw an exception when it is just invalid syntax... at least not that I can see. It simply returns the default error page from the server, whether it is Tomcat, Glassfish, etc.
So my question is how can I "intercept" Spring and cause it to use my exception handler or otherwise prevent the error page from displaying and instead return a JSON error object?
Here is my code:
#RequestMapping(value = "/trackingNumbers", method = RequestMethod.POST, consumes = "application/json")
#ResponseBody
public ResponseEntity<String> setTrackingNumber(#RequestBody TrackingNumber trackingNumber) {
HttpStatus status = null;
ResponseStatus responseStatus = null;
String result = null;
ObjectMapper mapper = new ObjectMapper();
trackingNumbersService.setTrackingNumber(trackingNumber);
status = HttpStatus.CREATED;
result = trackingNumber.getCompany();
ResponseEntity<String> response = new ResponseEntity<String>(result, status);
return response;
}
#ExceptionHandler({NullPointerException.class, EOFException.class})
#ResponseBody
public ResponseEntity<String> resolveException()
{
HttpStatus status = null;
ResponseStatus responseStatus = null;
String result = null;
ObjectMapper mapper = new ObjectMapper();
responseStatus = new ResponseStatus("400", "That is not a valid form for a TrackingNumber object " +
"({\"company\":\"EXAMPLE\",\"pro_bill_id\":\"EXAMPLE123\",\"tracking_num\":\"EXAMPLE123\"})");
status = HttpStatus.BAD_REQUEST;
try {
result = mapper.writeValueAsString(responseStatus);
} catch (IOException e1) {
e1.printStackTrace();
}
ResponseEntity<String> response = new ResponseEntity<String>(result, status);
return response;
}

This was raised as an issue with Spring SPR-7439 - JSON (jackson) #RequestBody marshalling throws awkward exception - which was fixed in Spring 3.1M2 by having Spring throw a org.springframework.http.converter.HttpMessageNotReadableException in the case of a missing or invalid message body.
In your code you cannot create a ResponseStatus since it is abstract but I tested catching this exception with a simpler method locally with Spring 3.2.0.RELEASE running on Jetty 9.0.3.v20130506.
#ExceptionHandler({org.springframework.http.converter.HttpMessageNotReadableException.class})
#ResponseStatus(HttpStatus.BAD_REQUEST)
#ResponseBody
public String resolveException() {
return "error";
}
and I received a 400 status "error" String response.
The defect was discussed on this Spring forum post.
Note: I started testing with Jetty 9.0.0.M4 but that had some other internal issues stopping the #ExceptionHandler completing, so depending on your container (Jetty, Tomcat, other) version you might need to get a newer version that plays nicely with whatever version of Spring you are using.