RestTemplate and WebClient: Future of RESTful Web Development

RestTemplate is not disappearing; it enters maintenance mode in Spring 5, with no plans for deprecation or removal in Spring 6.

### The Truth About RestTemplate and WebClient in Spring 6
* 🚫 Contrary to popular belief, RestTemplate has not been deprecated and will likely be supported until **at least Spring 7.0**.
* 🔄 RestTemplate has transitioned into a maintenance mode since Spring 5.0, with no new features planned, but it remains a **viable option for traditional synchronous Spring MVC development**.
* 🕵 The misconception that RestTemplate is disappearing likely stemmed from various documents and blogs hinting at its **deprecation**.
* 📝 An official source stating RestTemplate's deprecation was **sneakily removed** in a commit on **February 12, 2020**.
* 🌐 WebClient is recommended for modern API consumption and supports **sync, async, and async streaming modes**, but it may not provide **significant performance benefits** for traditional **synchronous use cases**.
* 📈 The newly introduced HTTP interface in Spring 6 allows API client code to be generated automatically by defining interfaces with annotations, **similar to Spring Data JPA repositories**.
* ✅ It's advisable to try both **RestTemplate** and **WebClient** in your team and choose the one that **best fits your use case**.
* 🛠 ️ The live coding session will demonstrate how to use the **HTTP interface** in **Spring 6**.

In Spring 3.0, one of the technologies that has been receiving a lot of love is RestTemplate. You are probably familiar with it. When we create a feature in a server program that calls another API, like an HTTP API, what do we usually use? Most of the time, we use RestTemplate. However, last week and even today in the cheerful Spring chatroom, I heard someone saying, Is RestTemplate going to disappear? They mentioned this kind of thing. Last week, someone asked me a question saying that RestTemplate is going to be removed, so don't use it, use WebClient instead. But WebClient doesn't come out by just adding the Spring Web module to the project, so you need to add the Spring WebFlux module.

You need to add it. If it's Spring Boot, you need to add the one called WebFlux starter to be able to use a web client. Now, what he's saying is, I just want to do traditional servlet-based web development with Spring MVC, but since the WebClientRestTemplate is gone, I'm afraid to use it. And then they say to use WebClient instead, but when I try to use WebClient, the entire Spring WebFlux module comes in, along with a lot of libraries. So, it feels a bit burdensome, and I'm wondering what to do. He asked this kind of question. So, what do you think? The topic of WebClient OpenFeign also came up. Now, let me talk about the history and the current situation, and many people, not only Spring developers in Korea, but also many people.

There is a misunderstanding even among many people overseas. Whether there is a problem with this or because the complete technology for this has now emerged, it is not recommended to use it anymore. Next, this will be completely removed around the next version or the version after that. Don't use it. This is about not using it. The deprecated annotation that says not to use it is already included. What do you think in general documents? For example, if I use WebFlux, then you must use a web client. But I don't want to develop in a reactive way like WebFlux. I just want to do traditional Spring MVC development. Is it not allowed to use RestTemplate here from Spring 5? This was mentioned from Spring 5, but what about now, with Spring 6? Let's talk about it.

I wanted to say, so when I heard that story, I thought it was a bit strange. They are using RestTemplate well, so why is it disappearing? Why did you think that? Where did you hear that? Who is spreading fake news, rumors, or something like that? So, I got curious and searched on Google. After searching, I found a lot of results. Many documents containing that information appeared, and they were quite famous and authoritative sources. It seems like it even appears in search results from places like Melden. So, I guess that's where this information is coming from. Therefore, I went in and looked at the document. Where is it? Since when has it been saying that starting from Spring 5 and with the emergence of the web client, this will no longer be available, so do not use it anymore. Such a statement is written on a seemingly innocent blog. Also, now that I've looked into it.

Dodo of Linkin wrote an article, and here, maybe here, it's all in the title. So, what's next? I don't know what he's talking about, but why does this come up? Why do they keep talking about this? So, what on earth is this about? Oh, it's not mentioned here. Why did the search come up? Well, it's probably because of introducing the WebClient and such. So, now we need to find the exact source. If it's in the official document, Spring Reference Manual, or the RestTemplate City Predicate, it will have a source code diffication attached. And since it difricates on JavaDoc Connect, it will probably be removed around the next version. Don't use it. That's the kind of talk that should be in there. So, I looked it up. I downloaded the Spring source code, the latest Spring source code, version 6.0.6, now.

When you go in and look, the explanation is quite lengthy, but the key part is probably the section labeled Notes below. So, from 5.0, this class rest template goes into the maintenance board and only does maintenance. What I mean is, in case there are serious security or significant issues, you can fix bugs of that level, but there are no plans to add new features or further develop here. And now, the following discussion is to consider using it for web clients. It supports much more modern APIs. Furthermore, it supports three scenarios: sync, async, and sync streaming modes. It covers all the way to async streaming, so it's really great. Use this. This is how it's being discussed. So, the latter part is similar to what I've heard.

Correct, but I can't find the word difricated anywhere here. Does it exist? Let me search just in case. Deprecated is here, which means the execute method is deprecated in Spring. It doesn't mean this class is deprecated, so in conclusion, RestTemplate will not disappear, it has not been deprecated. This means it will likely still be alive at least until Spring 7.0 comes out. Usually, once a major version goes up, they mark it as deprecated, and it tends to disappear around the time the next major version comes out. So, since it hasn't been attached up to 6.0, it will naturally not disappear in 6.0, and probably not in 7.0 either. When we get there, we might deprecate it, but that's uncertain. So, why do people say RestTemplate will disappear?

Because it might disappear when I do it, I'm scared of this, so I can't write it. I should use a web client, but now I like web flight, and I was very interested in developing with WebFlux or reactive, so I looked into this in detail. It's good, but in the traditional way of web development, just using it as a Spring MVC synchronous method, there are not many advantages to using a web client. Even if the WebClient section runs asynchronously in terms of performance, it doesn't really speed up the overall performance. On the contrary, it just makes it a bit slower. The good thing is that the API is more modern, so if you just use it simply in the WebClient template, it's fine. But if you insert things like headers, you have to create a request entity and create headers.

Inserting it and the code is a bit, how should I say, messy, but these days, we continue writing in a format we like, chaining with dots, so that we can complete one task before the sentence ends. In that aspect, it's more convenient. Moreover, now it can be used in an asynchronous manner when transitioning to Flux later, so there are advantages in using the same method. So, you can use a web client if you want, but personally, I'm fine with just the traditional REST template. This is supported by Spring, of course, it hasn't been discontinued, and Spring Boot also supports it well. Basically, when using Spring Boot, you have the REST template registered by default, so you can just use it, which is quite convenient. But why are these kinds of discussions coming up now, I wonder.

Now, someone said something wrong, and it spread like that. I used to think that way, but when I traced it, I found that there was actually a mention in the Spring official documentation that the rest template is deprecated. What I discovered yesterday while tracing this was that... And, oh, what is new is that no new features will be added, it will enter maintenance mode. Although it says the same thing, it clearly indicates that it is deprecated. It's shocking. So, for those of you who see this, you might think, Oh, so the template is disappearing, and this could cause a big problem. Some may think, Well, we have to use WebClient then. Some might think, Well, until it really disappears, it's supported, so let's use it for now.

It will be there, and that's why those documents and blogs I found on Google search will be duplicated in templates. They will disappear in the future. Don't use them anymore. Such advice is starting to come out now. But the interesting thing is that on February 12, 2020, when you look at the computer, it has changed. How did it change? The content disappears. They sneakily removed it. What exactly happened in between? Oh, originally, I was going to duplicate and remove this, but my mind changed. Oh, this won't work. I have to leave it. It's too perfect. Even if I don't add any additional features, I have to maintain it. This is how developers bring changes in their mindset and sneakily make changes. If you want to know a bit about this, about commits, what is it usually for now to handle some issues.

Make corrections and add issue numbers, usually creating a commit log. So, if you open this on GitHub and track it like this, you can see that this commit was made to close the issue. By following the issue, you can see what discussions led to this decision. It turns out there wasn't much discussion. Rossen Stoyanchev and Brian Clozel, thanks to the code that Brian Clozel uploaded as a PR, it was included in the Spring Web Test project, and later when it merged into the Spring Core, the code written by Brian Clozel was included in the Spring Core framework. In fact, this person has been leading the Spring MVC project and Spring Web Flux practically after version 3.0. So, you can consider him as the lead role player. What did this person discuss about the issue?

It would be much better to just say it's in maintenance mode rather than saying it's now deprecated. That would be more helpful, and what's more important is that it's more accurate. Saying it's accurate means we didn't plan to deprecate it. We weren't planning to do that originally. We just pushed towards WebFlux with the release of Spring 5.0. We thought Reactor was great, we pushed hard on it, but it didn't really catch on. There weren't as many WebFlux users as we thought, and there were various reasons for that. Anyway, in my opinion, I don't think the Spring core developers working on the Spring web side were planning to get rid of it. That's how I express it. Hey, now we're all going to the reactive world, and from there.

Now, since the web client will be the main one, RestTemplate may disappear. So, I probably left a comment there, but that's not accurate. Explaining it like that won't be helpful. So, I changed it. So, I briefly mentioned the issue and changed the comment as before. It's already been three years since that, in 2020, February, not 2001, 2 or 3 years ago. But developers still believe in stories that spread from old memories. Since RestTemplate will be gone in the future, web clients must be used. So, please don't misunderstand. This is a very simple story, so I think we can finish here. So, in my opinion, about RestTemplate and web...

Clients, you must be curious about the pros and cons, when to use it, what is a better choice for the future, and so on. Let me confess a bit, and then in Spring 6, in Spring 5, there were two rest clients. Do you happen to know what they are? In Spring 6, there is a new rest client technology added. If anyone knows about it, please leave a comment in the chat. Now, here in the latest documentation for Spring 6.0, there are two options, and now a third one, the HTTP interface, has been added. I'm not sure if any of you have used openfeign-like libraries, or maybe in places like Android, this style of code is used a lot. It means just defining interfaces. When you use Spring Data JPA, you only create interfaces for the repository, right? Then the implementation for that is...

Dynamic automatically, now frameworks create many technologies like this are commonly used, and how it works is defined only by annotations. Similarly, just like that, if you create an interface with annotations for the client code that calls the API, all the client code that actually calls it is automatically generated. This technology has officially entered Spring 6. Therefore, it is called the HTTP interface. This is used a lot in Android. Anyway, the HTTP interface has been introduced, so let's take a look at roughly how the code looks when written with this. First of all, the West template does not disappear, so you can just use it comfortably. You can continue to use it as you like. While the client provides convenience, there are also inconveniences.

Yes, please try both of them, and if you use both of them in the team, it might be a bit, so choose one and use it. Now, I will try a simple live coding session. This is a new one.

RestTemplate은 스프링에서 제거되나요?

토비의 스프링 

The Transition from RestTemplate to WebClient in Spring Development

RestTemplate, commonly used for calling HTTP APIs in server programs, is facing rumors of being discontinued in favor of WebClient.

The use of WebClient requires adding the Spring WebFlux module, which may seem burdensome for those wanting to stick to traditional servlet-based development.

The rumored transition from RestTemplate to WebClient is causing confusion and concern among Spring developers, despite being based on information from authoritative sources and search results.

The RestTemplate class in the Spring framework is not being deprecated in version 6.

0 and is unlikely to disappear in version 7.

The class will continue to receive maintenance for serious issues but will not have new features added.

The discussion is ongoing about whether to use RestTemplate for web clients, with the WebClient offering more modern APIs and support for sync, async, and sync streaming modes.

The Evolution of the REST Template in Spring Development

The REST template has been a preferred format for its convenience in completing tasks.

However, it has been deprecated in the Spring official documentation, indicating no new features will be added, and it will enter maintenance mode.

This has led to discussions on transitioning to WebClient as the REST template is gradually being phased out.

Update on Spring Framework Maintenance and Web Client Transition

Brian Clozel's code, initially part of the Spring Web Test project, was later integrated into the Spring Core framework, where he has played a leading role in the Spring MVC project and Spring Web Flux.

The Spring Core developers did not originally plan to deprecate the WebFlux framework, but due to its limited adoption, they are now transitioning towards the reactive world, indicating that RestTemplate may be phased out in the future.

The discussion also clarifies that the changes are not set to happen immediately, and there is still a lingering belief in older development practices.

The Introduction of the HTTP Interface in Spring 6.

0, a new HTTP interface has been added as a third option for rest clients, allowing for the automatic generation of client code through interface annotations.

This technology, commonly used in Android, provides convenience but may also bring some inconveniences.

It is now a choice alongside the existing rest client options, such as the West template, for calling APIs in Spring 6.