Java

implementation 'com.fasterxml.jackson.core:jackson-databind:2.16.0'

<dependency>
  <groupId>com.fasterxml.jackson.core</groupId>
  <artifactId>jackson-databind</artifactId>
  <version>2.16.0</version>
</dependency>

// src/main/java/com/example/vtilt/Vtilt.java
package com.example.vtilt;

import com.fasterxml.jackson.databind.ObjectMapper;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.time.Duration;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.Executors;
import java.util.concurrent.ExecutorService;

public final class Vtilt {
    private static final String TOKEN = System.getenv("VTILT_TOKEN");
    private static final String HOST = System.getenv().getOrDefault("VTILT_HOST", "https://www.vtilt.com");
    private static final ObjectMapper MAPPER = new ObjectMapper();
    private static final HttpClient CLIENT = HttpClient.newBuilder()
            .connectTimeout(Duration.ofSeconds(2))
            .build();
    private static final ExecutorService EXEC = Executors.newVirtualThreadPerTaskExecutor();

    private Vtilt() {}

    public static void capture(String distinctId, String event, Map<String, Object> properties) {
        EXEC.submit(() -> send(distinctId, event, properties == null ? Map.of() : properties));
    }

    public static void identify(String distinctId, Map<String, Object> properties) {
        capture(distinctId, "$identify", Map.of("$set", properties));
    }

    private static void send(String distinctId, String event, Map<String, Object> properties) {
        try {
            Map<String, Object> body = new HashMap<>();
            body.put("api_key", TOKEN);
            body.put("event", event);
            body.put("distinct_id", distinctId);
            body.put("properties", properties);

            HttpRequest req = HttpRequest.newBuilder(URI.create(HOST + "/api/e"))
                    .header("Content-Type", "application/json")
                    .timeout(Duration.ofSeconds(2))
                    .POST(HttpRequest.BodyPublishers.ofString(MAPPER.writeValueAsString(body)))
                    .build();

            CLIENT.send(req, HttpResponse.BodyHandlers.discarding());
        } catch (Exception ignored) {
            // never raise on analytics
        }
    }
}

import com.example.vtilt.Vtilt;
import java.util.Map;

public class CheckoutService {
    public void completePurchase(String userId, double amount) {
        Vtilt.identify(userId, Map.of("plan", "pro"));

        Vtilt.capture(userId, "purchase_completed", Map.of(
            "amount", amount,
            "currency", "USD"
        ));
    }
}

@RestController
public class CheckoutController {

    @PostMapping("/checkout")
    public Map<String, Boolean> complete(@RequestBody CheckoutRequest req) {
        Vtilt.capture(req.userId(), "purchase_completed", Map.of("amount", req.amount()));
        return Map.of("ok", true);
    }
}