As per spring 5:
WebClient is an interface representing the main entry point for performing web requests.
It has been created as a part of the Spring Web Reactive module and will be replacing the classic RestTemplate in these scenarios. The new client is a reactive, non-blocking solution that works over the HTTP/1.1 protocol
Does that mean, we need to recode for the old applications using RestTemplate if we want to upgrade to Spring 5?
Or there is some workaround to work with RestTemplate in Spring 5?
No, RestTemplate will continue to exist (at least for now). You don't have to replace it with WebClient.
One of the main differences is RestTemplate is synchronous and blocking i.e. when you do a rest call you need to wait till the response comes back to proceed further.
But WebClient is complete opposite of this. The caller need not wait till response comes back. Instead he will be notified when there is a response.
If you need such a functionality, then yes you need to replace your Resttemplate with WebClient.
You can in fact achieve Rest template like synchronous processing in webclient using .block(). But the other way is not possible.
EDIT:
RestTemplate will be deprecated in a future version(> 5.0) and will not have major new features added going forward
According to the Java Doc the RestTemplate will be in maintenance mode. Spring team advise to use the WebClient if possible:
NOTE: As of 5.0, the non-blocking, reactive
org.springframework.web.reactive.client.WebClient offers a modern
alternative to the RestTemplate with efficient support for both sync
and async, as well as streaming scenarios. The RestTemplate will be
deprecated in a future version and will not have major new features
added going forward.
RestTemplate is not really deprecated. But it will not be evolved in the future. So sticking to RestTemplate is perfectly valid if it does what you need.
Another way to put that is that if you need specific usage patterns like streaming, scatter/gatter, or custom timeouts, this won't be covered by RestTemplate and you need to use WebClient instead.
Now using WebClient in a blocking application is fine too. Using block() shouldn't hurt there and Spring MVC controller does partially support reactive return types.
WebClient is Non-Blocking Client, RestTemplate is Blocking Client.
For a long time, spring serves as a web customer. Under the hood, RestTemplate uses the Java API API, which is based on the subject model.This means that the matter will be blocked until the client receives a response. The problem with the blockage code is due to the existence of any string of memory and cpu cycles. Let us consider a lot of applications that are waiting for low services that are needed to produce the result.Sooner or later, requests for the results are collected. As a result, the program creates many issues, which result in depletion of a pool of thread or occupying all of the available memory. We can also experience performance performance due to the cpu switching.
Spring WebClient vs. RestTemplate
WebClient supports asynchronous as well as synchronous calls.
RestTemplate supports only synchronous calls.
No changes are required in old code even if the RestTemplate is depracated(as long as you don't need asynchronous behaviour)
Related
Why is Spring KafkaTemplate implemented in an asynchronous way? Do we have any other Spring implementation of it that is synchronous? I don't want to use futureTask.get() to make is seem synchronous
You probably miss the fact that Spring for Apache Kafka is nothing more than convenient Spring-friendly API around standard Kafka Client. And that's already a Producer.send() API to return for us a Future making all the stack as asynchronous. So, even if someone would do a synchronous API for you it still would do that futureTask.get() underneath.
I want to use Spring WebClient in a project to consume some external web service.
Can WebClient object be singleton or shared among all threads (requests)?
If my application is going to get millions of requests per second, then do I need to pool WebClient Objects? If yes, I am unable to find any documentation or examples.
Does mono.block() internally work similar to future.get() or latch.await()?
The WebClient is a non-blocking implementation of a REST client built on the Reactive Stack, so I guess the only issue you should focus on is to complete a non-blocking call.
Can WebClient object be a singleton or shared among all threads (requests)?
A standard way I have seen everywhere is to inject WebClient as a bean. I find no reason to do any different.
#Autowired
WebClient webClient;
If my application is going to get millions of requests per second, then do I need to pool WebClient Objects?
That's a lot! This should definitely need to be solved with service replication, load-balancers, bulkhead, etc. In terms of the client itself, see the following performance of reactive client using newer versions of Spring: WebFlux Reactive Programming Performance Test. Moreover, that is the expected maximal throughput?
Does mono.block() internally work similar to future.get() or latch.await()?
Yes, it does.
Background : I am using spring boot with embedded jetty. My app calls bunch of rest apis. For calling these rest apis I use spring rest template.
Question: Is Spring rest template any good at high concurrency? Searching on the web search suggests moving to reactive but still there are apps which are written in blocking way and need to continue that way. Question is what alternate is there or what can be done to make rest template more responsive under heavy load. PoolingHttpClientConnectionManager improves things a bit but essentially still not at par with is required.
There are suggestions to move to rest easy and other http clients but no slid reasoning behind it. End of the day, they all make pool of connections and essentially works the same. Please note, reactive is not an option yet. This question is very specific to traditional blocking rest calls. Any suggestions in optimizing connection pooling or using rest template right will be of great help.
RestTemplate does not do an actual rest call by itself, its just a "wrapper" - a convenient API.
Now when it comes to connection pooling, by default it doesn't use any kind of pooling and just opens URL connections available in Java anyway. No third-parties are required, but performance is not so good.
You can configure rest template to use, say, OkHttp Client under the hood. See here for different ways to work with different clients. The interesting part is that its possible to configure connection pools there and achieve a better performance.
So you should really check what exactly the expected performance is and configure the connection pool accordingly.
Now one more thing about Reactive stuff - it won't give you a performance gain, however it will allow to serve better multiple concurrent requests by reusing resources more efficiently. However if you'll measure how long it takes to perform one single request - its not expected to be performed faster.
In other words you should consider the transition to reactive stack if the application has too many concurrent requests that it can't serve, but not if you want to process every single request faster.
Spring RestTemplate is used to write application level code. It obtains the HTTP connection from ClientHttpRequestFactory implementation which is what glues low-level HTTP client library to Spring e.g. HttpComponentsClientHttpRequestFactory for Apache HTTP Client.
Bottom line, in most cases you have to tune the underlying low-level HTTP client library and not RestTemplate when you are tuning outgoing requests to external APIs.
You are confusing a lot of concepts in your question. Try understanding what is Reactive programming, HTTP, HTTP pipelining, and TCP/IP before you start tuning anything. Otherwise you won't find where is your code's bottleneck and you will end up tuning wrong part of the software stack.
I have some microservices, which should work on top of WebFlux framework. Each server has own API with Mono or Flux. We are using MongoDB, which is supported by Spring (Spring Data MongoDb Reactive).
The problem is external blocking API, which I have to use in my system.
I have one solution. I can just wrap blocking API calls in dedicated thread pool and use it with CompletableFuture.
Is there anything else to solve my problem? I think, that brand new Rsocket cannot solve my problem.
1.If possible, you can change your blocking API call to the reactive way using the WebClient class.
References:
Reference guide
WebClient API
A simple, complete sample
2.If the blocking API can't be changed to reactive ones, we should have a dedicated, well-tuned thread pool and isolate the blocking code there.
There is also an example here.
I don't see why you cannot wrap a blocking API call in a Flux or a Mono. You can also integrate Akka with Spring if the actor model seems easier to you.
RSocket should be a perfect fit, good tutorials to get you started
https://www.baeldung.com/spring-boot-rsocket
https://spring.io/blog/2020/04/06/getting-started-with-rsocket-spring-boot-channels
What is the proper way to make an api call via springs WebClient, but ignore the result? The ClientResponse object specifically calls out that I have to do something with the result...
Docs:
NOTE: When given access to a ClientResponse, through the WebClient exchange() method, you must always use one of the body or toEntity methods to ensure resources are released and avoid potential issues with HTTP connection pooling. You can use bodyToMono(Void.class) if no response content is expected. However keep in mind that if the response does have content, the connection will be closed and will not be placed back in the pool.
Can I make a WebClient call and ignore the results? or is there a generic catch all "body or toEntity method" that I can use and then ignore?
Prior to Spring Framework 5.2, using the WebClient#exchange() method and dealing directly with the Mono<ClientResponse> could be quite complex or lead to potential memory leaks.
As of Spring Framework 5.2, this has been made much easier for developers and the exchange() method has been deprecated.
Mono<ResponseEntity<Void>> response = webClient.put()
.uri("https://example.org/book/123")
.retrieve()
.toBodilessEntity();
Spring will read the response body (if present) and release the data buffers, and then return the connection to the pool. It's making sure that there's no memory leak, including when additional Reactor operators are used.