Callbacks

OkHttpClient client = new OkHttpClient().newBuilder().build();
RequestBody body = RequestBody.create(
  MediaType.parse("application/json"),
  "{" +
    "\"merchantTransactionId\": \"your-unique-identifier\"," +
    "\"description\": \"Purchase description shown on credit card statement.\"," +
    "\"amount\": \"9.99\"," +
    "\"currency\": \"EUR\"," +
    "\"successUrl\": \"https://shop.example.org/checkout/success\"," +
    "\"cancelUrl\": \"https://shop.example.org/checkout/cancelled\"," +
    "\"errorUrl\": \"https://shop.example.org/checkout/error\"," +
    "\"callbackUrl\": \"https://api.example.org/callback\"" +
  "}"
);
String auth = Base64.getEncoder().encodeToString(
  "%s:%s".format(System.getenv("USERNAME"), System.getenv("PASSWORD")));
Request request = new Request.Builder()
  .url("https://gateway.ixopay.com/api/v3/transaction/%s/debit"
    .format(System.getenv("API_KEY")))
  .method("POST", body)
  .addHeader("Content-Type", "application/json")
  .addHeader("Accept", "application/json")
  .addHeader("Authorization", "Basic %s".format(auth))
  .build();
Response response = client.newCall(request).execute();

import com.fasterxml.jackson.databind.JsonNode;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;
@SpringBootApplication
@RestController
public class Application {
  public static void main(String[] args) {
    SpringApplication.run(Application.class, args);
  }
  @PostMapping(path = "/callback",
    consumes = MediaType.APPLICATION_JSON, produces = MediaType.TEXT_PLAIN_VALUE)
  public ResponseEntity<String> callback(@RequestBody JsonNode json) {
    // TODO: handle callback
    // Return an "OK" response with a 200 status code
    return ResponseEntity.ok("OK");
  }
}

import com.fasterxml.jackson.databind.JsonNode;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.mail.SimpleMailMessage;
import org.springframework.mail.javamail.JavaMailSender;
import org.springframework.stereotype.Repository;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;
@SpringBootApplication
@RestController
public class Application {
  public static void main(String[] args) {
    SpringApplication.run(Application.class, args);
  }
  @Autowired
  private TransactionRepository transactionRepository;
  @Autowired
  private JavaMailSender mailSender;
  @PostMapping(path = "/callback",
    consumes = MediaType.APPLICATION_JSON, produces = MediaType.TEXT_PLAIN_VALUE)
  public ResponseEntity<String> callback(@RequestBody JsonNode json) {
    String transactionId = node.get("merchantTransactionId")
    String result = node.get("result");
    Transaction transaction = transactionRepository.findById(transactionId).orElse(null);
    if(transaction != null) {
      transaction.state = result;
      transactionRepository.save(transaction);
      if("OK".equals(transaction.state)) {
        SimpleMailMessage message = new SimpleMailMessage();
        message.setTo(transaction.customerEmail);
        message.setSubject("Order confirmed.");
        message.setText(
          "Your payment has been received.\n\nThe order has now been confirmed.");
        mailSender.send(message);
      }
    }
    // Return an "OK" response with a 200 status code
    return ResponseEntity.ok("OK");
  }
  @Entity
  @Table(name = "transaction")
  public static class Transaction {
    @Id
    private String id;
    @Column(name = "state")
    private String state;
    @Column(name = "customer_email")
    private String customerEmail;
    // ...
  }
  @Repository
  public static class TransactionRepository extends JpaRepository<Transaction, String> {
  }
}