The code for this microservice is a simple textbook REST service. This is a simple blocking service so that we can explore a simpler paradigm. Later we'll build a Webflux service when we build the Event Activity service. Here's the basic outline of the solution:
The client request
The client request is the input to the microservice REST API. It's a simplified json record with the basic requirements for sending emails. Any additional information required to build a SendGrid request are stored as configurations
POST /email/v2/send HTTP/1.1
Host: localhost:5000
Content-Type: application/json
Content-Length: 269
{
"senderName": "me",
"fromAddress": "sender@gmail.com",
"toAddress": "receiver@gmail.com",
"subject": "This is my email",
"content": "Click here to create a click event: http://www.google.com",
"customArgs": {
"mycounter": 60000
}
}
The Controller
The controller is a simple rest service that our client calls. It handles the client request by passing it on to the main program and returning the final result back to the client.
SendGridController.java
/*
You will often see examples where the Java object is passed as an object:
* ResponseEntity<String> handleRequest(@RequestBody SendgridRequest mailRequest)
letting Spring handle the json conversion implicitly - but some teams don't do it that way, preferring to
pass in the json string and manage the conversion
*/
@PostMapping(path = "/send")
public ResponseEntity<String> handleRequest(@RequestBody String mailRequest) {
HttpHeaders responseHeaders = new HttpHeaders();
responseHeaders.set("Content-Type", "application/json");
try {
String result =
controllerFacade.requestHandler(mailRequest);
return ResponseEntity.ok()
.headers(responseHeaders)
.body(result);
} catch (Exception e) {
return ResponseEntity.badRequest()
.headers(responseHeaders)
.body(e.getLocalizedMessage());
}
}
The Handler
The handler function is just a pass-through - it's only function is to convert from a json string to a SendgridRequest Object and to provide a final catch for any errant runtime exceptions. The design paradigm is that everything returning to the caller is in the form of a valid Response object.
public Response requestHandler(String jsonString) throws IOException {
try {
//---convert json ----
SendgridRequest mailRequest = objectMapper.readValue(jsonString, SendgridRequest.class);
//--- pass to Sendgrigmailr
var response = sendGridMailer.send(mailRequest);
// ---- handle bad response and return ---
if (response == null)
throw new NullPointerException("mailer returned unexpected null");
return response;
} catch (JsonProcessingException | IllegalArgumentException ex) {
return new Response(HttpStatus.BAD_REQUEST.value(), ex.getMessage(),
Map.of("Content-type", "application/json", "X-Source", "json-format"));
} catch (Exception ex) {
return new Response(HttpStatus.INTERNAL_SERVER_ERROR.value(), ex.getMessage(),
Map.of("Content-type", "application/json", "X-Source", "application-error"));
}
}
The Mailer
The SendGridMailer send() method takes the user's request and:
SendGridMailer.java
public Response send(SendgridRequest mailRequest) throws IOException {
// Create a SendGrid Mail object
Mail mailer = createSendGridMail(mailRequest);
// Create a SendGrid Request
final Request request = new Request();
request.setMethod(Method.POST);
request.setEndpoint("/" + apiVersion + "/" + "mail/send");
request.setBody(mailer.build());
request.setBaseUri(this.host);
request.addHeader("User-Agent", "sendgrid/" + apiVersion + ";java");
request.addHeader("Authorization", "Bearer " + apiKeyValue);
request.addHeader("Accept", "application/json");
// Send to the SendGrid API
try {
return client.api(request);
} catch (Exception e) {
return new Response(HttpStatus.BAD_GATEWAY.value(), e.getMessage(), request.getHeaders());
}
}
SendGrid Response
SendGrid will respond with an httpStatus code and any message in the body. It will aslo include a list of headers
