RestTemplate can only maintain two connections at a time

Question

My RestTemplate can only maintain two connections at a time. The 3rd request will be blocked until previous request(s) return.

I think something is wrong with RestTemplate bean configuration. Following is the configuration for RestTemplate:

TrustStrategy acceptingTrustStrategy = (X509Certificate[] chain, String authType) -> true;
SSLContext sslContext = new SSLContextBuilder()
        .loadTrustMaterial(null, acceptingTrustStrategy)
        .build();
SSLConnectionSocketFactory socketFactory = new SSLConnectionSocketFactory(sslContext);
CloseableHttpClient httpClient = HttpClients.custom()
        .setSSLSocketFactory(socketFactory)
        .build();
HttpComponentsClientHttpRequestFactory factory =
        new HttpComponentsClientHttpRequestFactory(httpClient);
return new RestTemplate(factory);

I can't figure out why. Please help.

Answer 1

Check this Baeldung guide where it says:

The default size of the pool of concurrent connections that can be open by the manager is two for each route or target host

But you can modify that property:

PoolingHttpClientConnectionManager connManager 
  = new PoolingHttpClientConnectionManager();
connManager.setMaxTotal(5); 
connManager.setDefaultMaxPerRoute(4);

Where:

• setMaxTotal(int max) – Set the maximum number of total open connections
• setDefaultMaxPerRoute(int max) – Set the maximum number of concurrent connections per route, which is two by default.

So you can inject the connManager configuration into httpClient:

CloseableHttpClient client = HttpClients.custom()
    .setConnectionManager(connManager)
    .setSSLSocketFactory(socketFactory)
    .build();