Enhance Istio Distributed Tracing with OpenTracing-eshop-checkout

eshop-checkout.java

@RequestMapping(value = "/checkout")
public String checkout(@RequestHeader HttpHeaders headers) {
    String result = "";
    // Use HTTP GET in this demo. In a real world use case,We should use HTTP POST
    // instead.
    // The three services are bundled in one jar for simplicity. To make it work,
    // define three services in Kubernets.
    result += restTemplate.exchange("http://inventory:8080/createOrder", HttpMethod.GET,
            new HttpEntity<>(passTracingHeader(headers)), String.class).getBody();
    result += "<BR>";
    result += restTemplate.exchange("http://billing:8080/payment", HttpMethod.GET,
            new HttpEntity<>(passTracingHeader(headers)), String.class).getBody();
    result += "<BR>";
    result += restTemplate.exchange("http://delivery:8080/arrangeDelivery", HttpMethod.GET,
            new HttpEntity<>(passTracingHeader(headers)), String.class).getBody();
    return result;
}

private HttpHeaders passTracingHeader(HttpHeaders headers) {
    HttpHeaders tracingHeaders = new HttpHeaders();
    extractHeader(headers, tracingHeaders, "x-request-id");
    extractHeader(headers, tracingHeaders, "x-b3-traceid");
    extractHeader(headers, tracingHeaders, "x-b3-spanid");
    extractHeader(headers, tracingHeaders, "x-b3-parentspanid");
    extractHeader(headers, tracingHeaders, "x-b3-sampled");
    extractHeader(headers, tracingHeaders, "x-b3-flags");
    extractHeader(headers, tracingHeaders, "x-ot-span-context");
    return tracingHeaders;
}