Introduction to Activities

An Activity is a function that executes a single, well-defined action (either short or long running), which handles operations that can fail. Here are some examples:

Sending e-mails
API calls
Database writes
Network requests

An Activity involves code that is prone to failure because if it fails (let’s say the API is down), Temporal automatically retries it over and over until it succeeds or until your customized retry or timeout configuration is hit.

You implement the Activity interfaces and methods within it.

Here are two Activities: one for withdrawing money and one for depositing money.

Activity Interface

import io.temporal.activity.ActivityInterface;
import io.temporal.activity.ActivityMethod;

@ActivityInterface
public interface ReimbursementActivities {
  @ActivityMethod
  boolean withdrawMoney(double amount);

  @ActivityMethod
  boolean depositMoney(double amount);
}

Activity Implementation

public class ReimbursementActivitiesImpl implements ReimbursementActivities {
    @Override
    public boolean withdrawMoney(double amount) {
      // This would usually contain code that is prone to failure, 
      // like an API call, but it is a print statement here for simplicity.
      System.out.println("Successfully withdrawn $" + amount);
      return true;
    }

    @Override
    public boolean depositMoney(double amount) {
      System.out.println("Successfully deposited $" + amount);
      return true;
    }
}

See our code in more detail here.