Client Module Code

Introduction

Usage of the client module can support a wide variety of integration patterns to the destination service.

Obtaining the URL.

The first thing required is to get the location of the api you wish to call. This is done using the Cluster interface, and passing a few parameters to a call to serviceToUrl.

static Cluster cluster = SingletonServiceFactory.getBean(Cluster.class);
// protocol, serviceId, environment, requestKey (load balancer key, not required in most cases)
String apiHost = cluster.serviceToUrl("https", "com.networknt.apib-1.0.0", tag, null);

Based on the location that the com.networknt.apib-1.0.0 service registers itself in the instance of consul pointed to from service.yml, it will return an https url to that one of the instances.

Calling the Service

1. Building the Request

Given a url, first open a connection to that server:

static Http2Client client = Http2Client.getInstance();
ClientConnection connection = client.connect(new URI(apiHost), Http2Client.WORKER, Http2Client.SSL, Http2Client.POOL, OptionMap.create(UndertowOptions.ENABLE_HTTP2, true)).get();

If the service fails to connect, an exception will be thrown. The next thing we want to do is get a reference to the response, build our latches for asynchronous processing, and generate a request.


// Get a reference to the response
final AtomicReference<ClientResponse> reference = new AtomicReference<>();
// We only expect one response, so close the latch after it's received.
final CountDownLatch latch = new CountDownLatch(1);

// Build the request object:
ClientRequest request = new ClientRequest().setMethod(Methods.GET).setPath(apiPath);

2. Security

If we needed to include Client Credential Authorization in the request as a standalone client, then the following can be added:

static boolean securityEnabled = (Boolean)securityConfig.get(JwtHelper.ENABLE_VERIFY_JWT);
if (securityEnabled) client.addCcToken(request);

And if we need to include and propagate tokens in a request, then we would use:

if (securityEnabled) client.propagateHeaders(request, httpServerExchange);

After we have these objects created, we now only have to send the request, and wait for the response.

3. Sending the request


// Send the request
connection.sendRequest(request, client.createClientCallback(reference, latch));

// Wait for the response, SLA is 100 milliseconds for example.
latch.await(100, TimeUnit.MILLISECONDS);


// Read the response.
ClientResponse response = reference.get();

Closing the connection, if necessary, could be done

FAQ

How would I get the HTTP response code of the request:

int statusCode = response.getResponseCode();

How would I get the body (content) of the response:

String responseBody = response.getAttachment(Http2Client.RESPONSE_BODY)

If that responseBody was in json, could I convert it to an object?

List<String> responseList = Config.getInstance().getMapper().readValue(responseBody, new TypeReference<List<String>>(){});