Overview

ROS Actions are defined in action/*.action files. For each action ROS requires to have 3 separate messages: Goal, Feedback, Result (see ROS documentation for defining action in ROS2 or ROS1). On top of that ROS will create for each such message an Action message where the original message (Goal, Feedback, Result) + action metadata is stored (goal id, status, etc.).

In order to work with ROS actions from jrosactionlib users need to:

1. Provide a mapping from ROS *.action file to corresponding jrosactionlib action definition class. Definition class is described by the interfaces: Action2Definition for ROS2 action files, Action1Definition for ROS1 action files.
2. Define all message classes which are part of action definition class defined above (see jrosclient Defining messages guide).

To simplify this process users are encouraged to use msgmonster application.

Examples

Execute actions

In this example we are going to execute actions in Fibonacci action server using Java.

Before moving further we need to create and run Fibonacci action server based on the instructions from ROS documentation:

• for ROS2 Writing an action server and client.
• for ROS1 Writing a Simple action server using the Execute Callback (you can chose to do this on C++ or Python)

Creating action definition

ROS action file Fibonacci.action looks something like this:

int32 order
---
int32[] sequence
---
int32[] partial_sequence

We need to map it to the corresponding jrosactionlib action definitions Java class. Use final results of these definitions for ROS2 or ROS1

Once Java action definition is created, it can be used to run ROS actions.

Executing actions

Once we have Fibonacci action definitions ready we can use them to execute actions on Fibonacci action server.

ROS2

Required Java dependencies:

• jros2client - Java client for ROS2
• jros2actionlib - client for ROS2 Actions

Code:

var clientFactory = new JRos2ClientFactory();
var actionlibFactory = new JRos2ActionFactory();
try (var client = clientFactory.createClient();
        var actionlibClient =
                actionlibFactory.createClient(
                        client, new FibonacciActionDefinition(), "fibonacci")) {
    var goal = new FibonacciGoalMessage().withOrder(13);
    var result = actionlibClient.sendGoalAsync(goal).get();
    System.out.println(result);
}

ROS1

Required Java dependencies:

• jros1client - Java client for ROS1
• jros1actionlib - client for ROS1 action server

var clientFactory = new JRos1ClientFactory();
var actionClientFactory = new JRos1ActionClientFactory();
try (var client = clientFactory.createClient("http://127.0.0.1:11311/");
       var actionClient = actionClientFactory
           .createClient(client, new FibonacciActionDefinition(), "fibonacci")) {
    var goal = new FibonacciGoalMessage().withOrder(new Int32Message().withData(5));
    var result = actionClient.sendGoalAsync(goal).get();
    System.out.println(result);
}

Run ROS2 action server

In this example we are going to:

• implement "jros_fibonacci" ROS action server in Java
• run "jros_fibonacci" and execute incoming goals from other ROS2 nodes

Code:

var clientFactory = new JRos2ClientFactory();
var actionlibFactory = new JRos2ActionFactory();
Function<Integer, int[]> fibo = order -> {
    var seq = new int[order];
    seq[0] = 1;
    if (seq.length == 1) return seq;
    seq[1] = 1;
    if (seq.length == 2) return seq;
    for (int i = 2; i < seq.length; i++) {
        seq[i] = seq[i - 1] + seq[i - 2];
    }
    return seq;
};
ActionHandler<FibonacciGoalMessage, FibonacciResultMessage> handler =
        goal -> {
            System.out.println("Received new goal " + goal);
            var result = new FibonacciResultMessage(fibo.apply(goal.order));
            System.out.println("Result " + result);
            return CompletableFuture.completedFuture(result);
        };
try (var client = clientFactory.createClient();
        var actionServer =
                actionlibFactory.createActionServer(
                        client, new FibonacciActionDefinition(), "jros_fibonacci", handler)) {
    actionServer.start();
    System.out.println("Press Enter to stop ROS Action Server...");
    System.in.read();
}

In terminal, use "ros2" command to send goals to "jros_fibonacci" Java action server:

Waiting for an action server to become available...
Sending goal:
     order: 10

Goal accepted with ID: 226d976848e249ae8dfd106dfd81a1f6

Result:
    sequence:
- 1
- 1
- 2
- 3
- 5
- 8
- 13
- 21
- 34
- 55

Goal finished with status: SUCCEEDED