Dropwizard Client

The dropwizard-client module provides you with two different performant, instrumented HTTP clients so you can integrate your service with other web services: Apache HttpClient, version 4.3 and Jersey Client, version 1.18.

Apache HttpClient, version 4.3

The underlying library for dropwizard-client is Apache’s HttpClient, a full-featured, well-tested HTTP client library.

To create a managed, instrumented HttpClient instance, your configuration class needs an HttpClientConfiguration instance:

public class ExampleConfiguration extends Configuration {
    @Valid
    @NotNull
    @JsonProperty
    private HttpClientConfiguration httpClient = new HttpClientConfiguration();

    public HttpClientConfiguration getHttpClientConfiguration() {
        return httpClient;
    }
}

Then, in your application’s run method, create a new HttpClientBuilder:

@Override
public void run(ExampleConfiguration config,
                Environment environment) {
    final HttpClient httpClient = new HttpClientBuilder(environment).using(config.getHttpClientConfiguration())
                                                                    .build();
    environment.addResource(new ExternalServiceResource(httpClient));
}

Metrics

Dropwizard’s HttpClientBuilder actually gives you an instrumented subclass which tracks the following pieces of data:

org.apache.http.conn.ClientConnectionManager.available-connections: The number the number idle connections ready to be used to execute requests.
org.apache.http.conn.ClientConnectionManager.leased-connections: The number of persistent connections currently being used to execut requests.
org.apache.http.conn.ClientConnectionManager.max-connections: The maximum number of allowed connections.
org.apache.http.conn.ClientConnectionManager.pending-connections: The number of connection requests being blocked awaiting a free connection
org.apache.http.client.HttpClient.get-requests: The rate at which GET requests are being sent.
org.apache.http.client.HttpClient.post-requests: The rate at which POST requests are being sent.
org.apache.http.client.HttpClient.head-requests: The rate at which HEAD requests are being sent.
org.apache.http.client.HttpClient.put-requests: The rate at which PUT requests are being sent.
org.apache.http.client.HttpClient.delete-requests: The rate at which DELETE requests are being sent.
org.apache.http.client.HttpClient.options-requests: The rate at which OPTIONS requests are being sent.
org.apache.http.client.HttpClient.trace-requests: The rate at which TRACE requests are being sent.
org.apache.http.client.HttpClient.connect-requests: The rate at which CONNECT requests are being sent.
org.apache.http.client.HttpClient.move-requests: The rate at which MOVE requests are being sent.
org.apache.http.client.HttpClient.patch-requests: The rate at which PATCH requests are being sent.
org.apache.http.client.HttpClient.other-requests: The rate at which requests with none of the above methods are being sent.

Note

The naming strategy for the metrics associated requests is configurable. Specifically, the last part e.g. get-requests. What is displayed is HttpClientMetricNameStrategies.METHOD_ONLY, you can also include the host via HttpClientMetricNameStrategies.HOST_AND_METHOD or a url without query string via HttpClientMetricNameStrategies.QUERYLESS_URL_AND_METHOD

Jersey Client, version 1.18

If HttpClient is too low-level for you, Dropwizard also supports Jersey’s Client API. Jersey’s Client allows you to use all of the server-side media type support that your service uses to, for example, deserialize application/json request entities as POJOs.

To create a managed, instrumented JerseyClient instance, your configuration class needs an JerseyClientConfiguration instance:

public class ExampleConfiguration extends Configuration {
    @Valid
    @NotNull
    @JsonProperty
    private JerseyClientConfiguration httpClient = new JerseyClientConfiguration();

    public JerseyClientConfiguration getJerseyClientConfiguration() {
        return httpClient;
    }
}

Then, in your service’s run method, create a new JerseyClientBuilder:

@Override
public void run(ExampleConfiguration config,
                Environment environment) {

    final Client client = new JerseyClientBuilder(environment).using(config.getJerseyClientConfiguration())
                                                              .build(getName());
    environment.addResource(new ExternalServiceResource(client));
}