GlobalTracer.register(tracer);
HttpClient httpClient = new TracingHttpClientBuilder()
    .build();

//custom configuration
HttpClient httpClient = new TracingHttpClientBuilder(
        redirectStrategy, 
        redirectHandlingDisabled,
        GlobalTracer.get(),
        spanDecorators)
    .build();

spanManager.activate(parentSpan); // called in the same thread as client.execute()
client.execute(new HttpGet("url"));

BasicHttpContext basicHttpContext = new BasicHttpContext();
basicHttpContext.setAttribute(Constants.PARENT_CONTEXT, parentSpan.context());
client.execute(new HttpGet("url"), basicHttpContext);