Redirect is not followed on 301 with default RestClient

[AntipovAndrey]

Default RestClient does not follow redirect (in case of 301 at least.
Response body is null

@RestController
class SampleController {

    @GetMapping("/first")
    fun redirectToSecond() = ResponseEntity
        .status(301)
        .header("Location", "/second")
        .build<Unit>()

    @GetMapping("/second")
    fun noRedirect() = "OK"
}

@Component
class Runner(
    @Value("\${server.port}")
    private val port: Int
) : ApplicationRunner {

    override fun run(args: ApplicationArguments?) {
        // this works: redirect is followed
        val entityWithRC = RestClient.builder(RestTemplate()) // <---- this
            .baseUrl("http://localhost:$port")
            .build()
            .get()
            .uri("/first")
            .retrieve()
            .toEntity<String>()

        // this does not work: redirect is not followed
        val entityWithDefaults = RestClient.builder()
            .baseUrl("http://localhost:$port")
            .build()
            .get()
            .uri("/first")
            .retrieve()
            .toEntity<String>()

        println(entityWithRC)
        println(entityWithDefaults)
    }
}

Console output:

<200 OK OK,OK,[Content-Type:"text/plain;charset=UTF-8", Content-Length:"2", Date:"Thu, 17 Oct 2024 14:39:00 GMT", Keep-Alive:"timeout=60", Connection:"keep-alive"]>
<301 MOVED_PERMANENTLY Moved Permanently,[content-length:"0", date:"Thu, 17 Oct 2024 14:39:00 GMT", location:"/second"]>

[bclozel]

Thanks for getting in touch. This behavior is by design.

RestTemplate will use by default the SimpleClientHttpRequestFactory (backed by java.net.HttpURLConnection), while the more recent RestClient is using by default the JdkClientHttpRequestFactory (backed by java.net.http.HttpClient).

In this case, java.net.HttpURLConnection and java.net.http.HttpClient have different behavior when it comes to following redirects. As a framework, our best option is to rely as much as possible on the clients defaults and not try to align all clients on a single behavior (it's impossible and it would be surprising to many).

You can get the behavior you want by configuring the request factory like this:

HttpClient httpClient = HttpClient.newBuilder().followRedirects(HttpClient.Redirect.NORMAL).build();
RestClient restClient = RestClient.builder().requestFactory(new JdkClientHttpRequestFactory(httpClient)).build();