Spring configurable, high performance, metered http client instances

Question

Coming from DropWizard I am used to its HttpClientConfiguration and I am baffled that in Spring Boot I cannot find some support for controlling in a similar manner http clie

Answer 1

Below is an example of configuring a HttpClient with a configuration class. It configures basic authentication for all requests through this RestTemplate as well as some tweaks to the pool.

HttpClientConfiguration.java

@Configuration
public class HttpClientConfiguration {

  private static final Logger log = LoggerFactory.getLogger(HttpClientConfiguration.class);

  @Autowired
  private Environment environment;

  @Bean
  public ClientHttpRequestFactory httpRequestFactory() {
    return new HttpComponentsClientHttpRequestFactory(httpClient());
  }

  @Bean
  public RestTemplate restTemplate() {
    RestTemplate restTemplate = new RestTemplate(httpRequestFactory());
    restTemplate.setInterceptors(ImmutableList.of((request, body, execution) -> {
      byte[] token = Base64.encodeBase64((format("%s:%s", environment.getProperty("fake.username"), environment.getProperty("fake.password"))).getBytes());
      request.getHeaders().add("Authorization", format("Basic %s", new String(token)));

      return execution.execute(request, body);
    }));

    return restTemplate;
  }

  @Bean
  public HttpClient httpClient() {
    PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager();

    // Get the poolMaxTotal value from our application[-?].yml or default to 10 if not explicitly set
    connectionManager.setMaxTotal(environment.getProperty("poolMaxTotal", Integer.class, 10));

    return HttpClientBuilder
      .create()
      .setConnectionManager(connectionManager)
      .build();
  }

  /**
   * Just for demonstration
   */
  @PostConstruct
  public void debug() {
    log.info("Pool max total: {}", environment.getProperty("poolMaxTotal", Integer.class));
  }
}

and an example application.yml

fake.username: test
fake.password: test
poolMaxTotal: 10

You can externalise configuration values to your application.yml as with poolMaxTotal etc. above.

To support different values per environment you can use Spring profiles. Using the example above, you could just create application-prod.yml with a "prod" specific value for poolMaxTotal. Then start your app with --spring.profiles.active=prod and the "prod" value will be used instead of your default value in application.yml. You can do this for however many environments you need.

application-prod.yml

poolMaxTotal: 20

For an async HttpClient, see here: http://vincentdevillers.blogspot.fr/2013/10/a-best-spring-asyncresttemplate.html