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.

Originally published at https://www.czetsuyatech.com/2022/03/spring-rest-how-to-create-a-pooled-resttemplate.html.