How to Implement Twilio Programmable Voice API in Java

Install Twilio Java Helper Library

• To interact with Twilio's API from within Java, you need to use the Twilio Java helper library. Add the Twilio library to your project using Maven or Gradle.

<dependency>
  <groupId>com.twilio.sdk</groupId>
  <artifactId>twilio</artifactId>
  <version>8.28.1</version>
</dependency>

Initialize Twilio Client

• Initialize your `TwilioRestClient` with your Account SID and Auth Token. These credentials can be found in the Twilio Console.

import com.twilio.Twilio;
import com.twilio.type.PhoneNumber;
import com.twilio.rest.api.v2010.account.Call;
import com.twilio.rest.api.v2010.account.Call.Status;

Twilio.init("YOUR_ACCOUNT_SID", "YOUR_AUTH_TOKEN");

Make a Phone Call

• Create a new call by specifying the `from` and `to` phone numbers and provide a URL to your TwiML Bin or XML endpoint for the call instructions.

Call call = Call.creator(
    new PhoneNumber("+1234567890"),  // To number
    new PhoneNumber("+0987654321"),  // From number
    new com.twilio.type.Twiml("<Response><Say>Hello, this is a test call!</Say></Response>")
).create();

System.out.println(call.getSid());

Receive a Phone Call

• To receive calls, configure your Twilio number's voice URL to point to a webhook endpoint in your application that returns valid TwiML instructions.
• Set up a web server endpoint to handle the incoming call. For instance, using Spring Boot:

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;
import com.twilio.twiml.voice.Say;
import com.twilio.twiml.voice.VoiceResponse;

@RestController
public class TwilioController {
    @RequestMapping(value = "/voice", method = RequestMethod.POST, produces = "application/xml")
    public String handleVoiceCall() {
        Say say = new Say.Builder("Hello, thanks for calling!").build();
        VoiceResponse response = new VoiceResponse.Builder().say(say).build();
        return response.toXml();
    }
}

End a Call Programmatically

• To end an active call, use the call SID and update its status to `completed`.

Call call = Call.updater("CAXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX")
                .setStatus(Status.COMPLETED)
                .update();

System.out.println(call.getStatus());

Monitor Call Events

• Twilio can send HTTP requests to your application when call status updates occur. Configure your webhook to handle statuses like `ringing`, `completed`, or `failed`.
• Here's how you might set up a simple logging endpoint:

import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class TwilioWebhookController {
    @RequestMapping("/events")
    public void handleTwilioEvents(@RequestBody String payload) {
        System.out.println("Received event: " + payload);
    }
}

Conclusion

• With these steps, you have implemented core functionalities of the Twilio Programmable Voice API using Java. Make sure to handle additional post-call actions such as logging or data processing to suit your application needs.