Add EventNotificationHandler example (#2129)

Author: xavdid-stripe

CHANGELOG.md

@@ -4,6 +4,7 @@
 This release changes the pinned API version to `2025-12-15.preview`.
 
 * [#2104](https://github.com/stripe/stripe-java/pull/2104) Add EventNotificationHandler
+  * This is a new, simplified way to handle event notifications (AKA thin event webhooks). Learn more in the docs: https://docs.stripe.com/webhooks/event-notification-handlers
 * [#2117](https://github.com/stripe/stripe-java/pull/2117) Update generated code for beta
   * Add support for new resources `reserve.Hold`, `reserve.Plan`, and `reserve.Release`
   * Add support for `list` and `retrieve` methods on resources `reserve.Hold` and `reserve.Release`

src/main/java/com/stripe/examples/EventNotificationHandlerEndpoint.java

@@ -0,0 +1,107 @@
+package com.stripe.examples;
+
+import com.stripe.StripeClient;
+import com.stripe.StripeEventNotificationHandler;
+import com.stripe.StripeEventNotificationHandler.UnhandledNotificationDetails;
+import com.stripe.events.V1BillingMeterErrorReportTriggeredEventNotification;
+import com.stripe.exception.StripeException;
+import com.stripe.model.billing.Meter;
+import com.stripe.model.v2.core.EventNotification;
+import com.sun.net.httpserver.HttpExchange;
+import com.sun.net.httpserver.HttpHandler;
+import com.sun.net.httpserver.HttpServer;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.net.InetSocketAddress;
+import java.nio.charset.StandardCharsets;
+
+/**
+ * Receive and process event notifications (AKA thin events) like
+ * "v1.billing.meter.error_report_triggered" using EventNotificationHandler.
+ *
+ * <p>In this example, we:
+ *
+ * <ul>
+ *   <li>write a fallback callback to handle unrecognized event notifications
+ *   <li>create a StripeClient called client
+ *   <li>Initialize an EventNotificationHandler with the client, webhook secret, and fallback
+ *       callback
+ *   <li>register a specific handler for the "v1.billing.meter.error_report_triggered" event
+ *       notification type
+ *   <li>use handler.handle() to process the received notification webhook body
+ * </ul>
+ */
+public class EventNotificationHandlerEndpoint {
+  private static final String API_KEY = System.getenv("STRIPE_API_KEY");
+  private static final String WEBHOOK_SECRET = System.getenv("WEBHOOK_SECRET");
+
+  private static final StripeClient client = new StripeClient(API_KEY);
+  private static final StripeEventNotificationHandler handler =
+      client.notificationHandler(
+          WEBHOOK_SECRET, EventNotificationHandlerEndpoint::fallbackCallback);
+
+  public static void main(String[] args) throws IOException {
+    handler.onV1BillingMeterErrorReportTriggered(
+        EventNotificationHandlerEndpoint::handleMeterErrors);
+
+    HttpServer server = HttpServer.create(new InetSocketAddress(4242), 0);
+    server.createContext("/webhook", new WebhookHandler());
+    server.setExecutor(null);
+    server.start();
+  }
+
+  private static void fallbackCallback(
+      EventNotification notif, StripeClient client, UnhandledNotificationDetails details) {
+    System.out.println("Received unhandled event notification type: " + notif.getType());
+  }
+
+  private static void handleMeterErrors(
+      V1BillingMeterErrorReportTriggeredEventNotification notif, StripeClient client) {
+    Meter meter;
+    try {
+      meter = notif.fetchRelatedObject();
+    } catch (StripeException e) {
+      // TODO Auto-generated catch block
+      e.printStackTrace();
+      return;
+    }
+    System.out.println("Handling meter error for meter: " + meter.getDisplayName());
+  }
+
+  static class WebhookHandler implements HttpHandler {
+    // For Java 1.8 compatibility
+    public static byte[] readAllBytes(InputStream inputStream) throws IOException {
+      final int bufLen = 1024;
+      byte[] buf = new byte[bufLen];
+      int readLen;
+
+      ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
+
+      while ((readLen = inputStream.read(buf, 0, bufLen)) != -1)
+        outputStream.write(buf, 0, readLen);
+
+      return outputStream.toByteArray();
+    }
+
+    @Override
+    public void handle(HttpExchange exchange) throws IOException {
+      if ("POST".equals(exchange.getRequestMethod())) {
+        InputStream requestBody = exchange.getRequestBody();
+        String webhookBody = new String(readAllBytes(requestBody), StandardCharsets.UTF_8);
+        String sigHeader = exchange.getRequestHeaders().getFirst("Stripe-Signature");
+
+        try {
+          handler.handle(webhookBody, sigHeader);
+
+          exchange.sendResponseHeaders(200, -1);
+        } catch (StripeException e) {
+          exchange.sendResponseHeaders(400, -1);
+        }
+      } else {
+        exchange.sendResponseHeaders(405, -1);
+      }
+      exchange.close();
+    }
+  }
+}