I have the following actix test app:

#[post("/split")]
async fn split(input: String) -> Json<Vec<String>> {
    let result: Vec<String> = Regex::new(r" +")
        .unwrap()
        .split(&input)
        .map(|x| String::from(x))
        .collect();
    Json(result)
}

#[actix_web::main]
async fn main() -> std::io::Result<()> {
    HttpServer::new(|| {
        App::new().service(split)
    })
    .workers(100)
    .bind(("127.0.0.1", 8080))
    ?.run()
    .await
}

And I have the functionally equivalent Spring Boot endpoint:

@RestController
public class SplitController {
    private final Pattern pattern = Pattern.compile(" +");
    @PostMapping(path = "/split")
    public List<String> split(@RequestBody String input) {
        return List.of(pattern.split(input));
    }
}

I have a large text that I am submitted in the benchmark. For Spring Boot, the average response time is 119 ms. For the actix version, the average response time is a whopping 921 ms.

I just started learning Rust a few days ago, so I likely might be doing something horribly wrong.

My first thought was that compiling the regular expression every time could be the problem, but Java does this as well. So, I am clueless as to the speed difference.

What am I doing wrong or what is the deal?

UPDATE:

Based on the great feedback that I got, here is the new code:

static REGEX: Lazy<Regex> = Lazy::new(|| Regex::new(r" +").unwrap());

#[post("/split")]
async fn split(input: String) -> HttpResponse {
    let result: Vec<&str> = REGEX
        .split(&input)
        .collect();
    HttpResponse::Ok().json(result)
}

I also updated the Spring Boot code to compile the regular expression only once:

@RestController
public class SplitController {
    private final Pattern pattern = Pattern.compile(" +");
    @PostMapping(path = "/split")
    public List<String> split(@RequestBody String input) {
        return List.of(pattern.split(" +"));
    }
}

The average response time over 100,000 requests:

Spring Boot - 143 ms, 1 GB RAM. I was able to get this app to run stably at 200 MB of RAM, but the average response time was 422 ms. This is with the default embedded Tomcat server. Less RAM and it starts failing.

actix - 58 ms, 80 MB RAM. There could still be some tuning for actix that I don't know about.

Thanks to everyone who helped out this Rust noob!

UPDATE 2: