Streaming your request and response bodies with Spring's HTTP interfaces

December 11th, 2025

2 minute read

Spring Spring boot Advent of Spring

Introduction

Spring Boot 4 has been released last month! Considering all the new features it has, I decided to write about these features throughout the month of December. It will be an advent of Spring Boot 4 related tips!

Spring Boot 4 introduced us to several new features, several of them improving the HTTP service interfaces. Things I covered so far were the possibility to easily configure them and the fact that you can easily integrate OAuth2.

Another new feature that was added is that these HTTP interfaces now also support the use of InputStream and OutputStream formats. This allows you to easily stream responses, which could be useful for sending over large data without having to keep it all in memory.

Example

Last time, I set up an HTTP interface client for GitHub. The implementation we had looked like this:

@ClientRegistrationId("github")
@HttpExchange("/user")
public interface UserClient {
    @GetExchange("/repos")
    List<GitHubRepository> getRepositories(@RequestParam String type);
}

In stead of returning a List<GitHubRepository>, we could also return an InputStream. For example:

@ClientRegistrationId("github")
@HttpExchange("/user")
public interface UserClient {
    @GetExchange("/repos")
    List<GitHubRepository> getRepositories(@RequestParam String type);

    @GetExchange("/repos")
    InputStream getRepositoriesInputStream(@RequestParam String type);
}

After that, we could write some code to copy the InputStream to a file. For example:

Files.copy(
    userClient.getRepositoriesInputStream("private"),
    Path.of("./response.json"),
    StandardCopyOption.REPLACE_EXISTING);

The result will be that once you run this code, a file called response.json will appear in your project directory. In this case, it isn’t very useful. However imagine that you’re retrieving a very large JSON response body, or a very large file in general. Is it a good idea to deserialize the JSON response to an object if you just need to store the response? Or better, is it a good idea to keep a large response in memory? The answer is probably “no”, which is why streaming your response with an InputStream could be very useful!

Similarly, you can pass an OutputStream as the request body of an HTTP interface, which would allow you to stream large files as part of the request.

Conclusion

Streaming your request and response bodies can be useful in certain scenarios. Doing that required you to use either RestClient or WebClient directly, as it wasn’t possible through HTTP interfaces. Luckily, Spring framework 7 and thus Spring Boot 4 changed that, and now allow you to use InputStream for response bodies and OutputStream for request bodies.

This blogpost is a part of the Advent of Spring Boot 2025 series.