RestTemplate. How to increase max tcp connections?

Question

I have RestTemplate:

@Bean(name = "restTemplateBean")
public RestTemplate restTemplate(RestTemplateBuilder builder) {
    return builder
            .interceptors(new HttpRequestInterceptor())
            .uriTemplateHandler(new DefaultUriBuilderFactory((host + ":" + port)))
            .build();
}

When I call a large number of times the RestTemplate (post requests, for example) it creates a maximum of 5 ~ 10 TCP connections. How could I increase the maximum number of connections created by RestTemplate?

Answer 1

You can take advantage of connection pooling with Apache's HttpClient. Use HttpClientBuilder and increasing maxConnPerRoute and maxConnTotal to reach the performance you're looking for:

@Bean
public HttpClientBuilder httpClientBuilder() {
    return HttpClients.custom()
            .setMaxConnPerRoute(PER_ROUTE)
            .setMaxConnTotal(TOTAL);
}

@Bean
public RestTemplate restTemplate(HttpClientBuilder httpClientBuilder) {
    HttpComponentsClientHttpRequestFactory requestFactory = new HttpComponentsClientHttpRequestFactory();

    requestFactory.setHttpClient(httpClientBuilder.build());
    
    return new RestTemplate(requestFactory);
}

maxConnPerRoute limits how many connections can be made to a single IP:port, and maxTotal limits the number of total connections that can be opened.