RestTemplate backed by Apache HttpClient Connection Pool. Addresses RestTemplate HttpConnection exhaustion. Note this implementation is not route tunable and should be expanded when tuning by route is required. Example error: I/O error on POST request for "https://someendpoint": Timeout waiting for connection from pool; nested exception is org.a…

ClientHttpPoolConfiguration.java

import org.apache.http.client.config.RequestConfig;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class ClientHttpPoolConfiguration {

    @Autowired
    private HttpConnectionPoolConfiguration poolConfiguration;

    @Bean
    public PoolingHttpClientConnectionManager poolingHttpClientConnectionManager() {
        PoolingHttpClientConnectionManager result = new PoolingHttpClientConnectionManager();
        result.setDefaultMaxPerRoute(poolConfiguration.getMaxPerRoute());
        result.setMaxTotal(poolConfiguration.getMaxTotal());
        return result;
    }

    @Bean
    public RequestConfig requestConfig() {
        RequestConfig result = RequestConfig.custom()
                .setConnectionRequestTimeout(poolConfiguration.getConnectionRequestTimeout())
                .setConnectTimeout(poolConfiguration.getConnectTimeout())
                .setSocketTimeout(poolConfiguration.getSocketTimeout())
                .build();
        return result;
    }

    @Bean
    public CloseableHttpClient httpClient(PoolingHttpClientConnectionManager poolingHttpClientConnectionManager,
                                          RequestConfig requestConfig) {
        CloseableHttpClient result = HttpClientBuilder
                .create()
                .setConnectionManager(poolingHttpClientConnectionManager)
                .setDefaultRequestConfig(requestConfig)
                .build();
        return result;
    }
}

dependency.pom

<dependency>
	<groupId>org.apache.httpcomponents</groupId>
	<artifactId>httpclient</artifactId>
	<version>4.5.3</version>
</dependency>

ExampleConsumingClient.java

import org.apache.http.client.HttpClient;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
import org.springframework.web.client.RestTemplate;

@Configuration
public class RestTemplateConfiguration {

    @Bean
    public RestTemplate restTemplate(HttpClient httpClient) {
        HttpComponentsClientHttpRequestFactory httpRequestFactory = new
                HttpComponentsClientHttpRequestFactory();
        httpRequestFactory.setHttpClient(httpClient);
        RestTemplate restTemplate = new RestTemplate(httpRequestFactory);
        restTemplate.setErrorHandler(new CustomErrorResponseHandler());
        return restTemplate;
    }
}

HttpConnectionPoolConfiguration.java

import lombok.Data;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;

@Component
@ConfigurationProperties(prefix = "httppool")
@Data
public class HttpConnectionPoolConfiguration {

    private Integer maxPerRoute;
    private Integer maxTotal;
    private Integer connectionRequestTimeout;
    private Integer connectTimeout;
    private Integer socketTimeout;

}

httppoolconfig.yml

httppool:
  maxPerRoute: 100
  maxTotal: 1000
  connectionRequestTimeout: 300
  connectTimeout: 300
  socketTimeout: 1500