Java webhook signature example

WebhookExample.java

package com.gocardless.example;

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;

public class WebhookExample {
    public static void main(String[] args) throws Exception {
        String apiSecret = "ElfJ-3tF9I_zutNVK2lBABQrw-BgAhkZKIlvmbgk";
        String webhookBody = "{\"events\":[{\"id\":\"EV0000ED6V59V1\",\"created_at\":\"2015-04-17T15:24:26.817Z\",\"resource_type\":\"payments\",\"action\":\"submitted\",\"links\":{\"payment\":\"PM00008Q30R2BR\"},\"details\":{\"origin\":\"gocardless\",\"cause\":\"payment_submitted\",\"description\":\"The payment has now been submitted to the banks, and cannot be cancelled. [SANDBOX TRANSITION]\"},\"metadata\":{}},{\"id\":\"EV0000ED6WBEQ0\",\"created_at\":\"2015-04-17T15:24:26.848Z\",\"resource_type\":\"payments\",\"action\":\"confirmed\",\"links\":{\"payment\":\"PM00008Q30R2BR\"},\"details\":{\"origin\":\"gocardless\",\"cause\":\"payment_confirmed\",\"description\":\"Enough time has passed since the payment was submitted for the banks to return an error, so this payment is now confirmed. [SANDBOX TRANSITION]\"},\"metadata\":{}}]}";

        SecretKeySpec keySpec = new SecretKeySpec(apiSecret.getBytes("UTF-8"), "HmacSHA256");
        Mac mac = Mac.getInstance("HmacSHA256");
        mac.init(keySpec);

        byte[] bytes = mac.doFinal(webhookBody.getBytes("UTF-8"));

        StringBuilder builder = new StringBuilder();

        for (byte b : bytes) {
            builder.append(String.format("%02x", b));
        }

        String signature = builder.toString();
        System.out.println(signature); // 4d48a688e8bd6c313e3eecc78fa55b3e4ae23c65e70cf35038010f47742fb670
    }
}