How to Create a Pooled RestTemplate in Spring

To create a pooled RestTemplate we need to use HttpComponentsClientHttpRequestFactory which uses CloseableHttpClient from httpclient library (at least version 4.3 to support timeout.

1. Dependencies

<dependency>
  <groupId>org.apache.httpcomponents</groupId>
  <artifactId>httpclient</artifactId>
</dependency>

2. Create HttpComponentsClientHttpRequestFactory

private HttpComponentsClientHttpRequestFactory newHttpComponentsClientHttpRequestFactory() {

    final PoolingHttpClientConnectionManager poolingHttpClientConnectionManager =
        new PoolingHttpClientConnectionManager();
    poolingHttpClientConnectionManager.setDefaultMaxPerRoute(100);
    poolingHttpClientConnectionManager.setMaxTotal(100);

    final RequestConfig requestConfig = RequestConfig.custom()
        .setConnectionRequestTimeout(100)
        .setConnectTimeout(100)
        .setSocketTimeout(100)
        .build();

    CloseableHttpClient closeableHttpClient = HttpClientBuilder.create()
        .setConnectionManager(poolingHttpClientConnectionManager)
        .setDefaultRequestConfig(requestConfig)
        .build();

    final HttpComponentsClientHttpRequestFactory httpRequestFactory =
        new HttpComponentsClientHttpRequestFactory();

    httpRequestFactory.setConnectionRequestTimeout(connectionRequestTimeout);
    httpRequestFactory.setConnectTimeout(100);
    httpRequestFactory.setReadTimeout(100);

    httpRequestFactory.setHttpClient(closeableHttpClient);

    return httpRequestFactory;
  }

3. Create RestTemplate

private RestTemplate newRestTemplate(final HttpComponentsClientHttpRequestFactory httpComponentsClientHttpRequestFactory) {

    ObjectMapper objectMapper = new ObjectMapper();
    objectMapper.registerModule(new Jackson2HalModule());
    objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

    MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter = new MappingJackson2HttpMessagemappingJackson2HttpMessageConverter();
    mappingJackson2HttpMessageConverter.setSupportedMediaTypes(Arrays.asList(MediaTypes.HAL_JSON, MediaType.APPLICATION_JSON));
    mappingJackson2HttpMessageConverter.setObjectobjectMapper(objectMapper);

    final DefaultUriBuilderFactory defaultUriBuilderFactory = new DefaultUriBuilderFactory();
    defaultUriBuilderFactory.setEncodingMode(DefaultUriBuilderFactory.EncodingMode.VALUES_ONLY);

    return new RestTemplateBuilder()
        .messagemappingJackson2HttpMessageConverters(mappingJackson2HttpMessageConverter)
        .rootUri(baseUrl)
        .uriTemplateHandler(defaultUriBuilderFactory)
        .requestFactory(() -> httpComponentsClientHttpRequestFactory)
        .build();
  }

4. How to use

final RestTemplate restTemplate = newRestTemplate(newHttpComponentsClientHttpRequestFactory());

5. Improvements

Create a Configuration class for the number values.