Overview

In ROS, messages which are used to communicate with ROS Services are defined in srv/*.srv files. Each service requires 2 messages: Request, Response (see ROS documentation for defining services in ROS2 or ROS1.

In order to work with ROS Services from jrosservices users need to:

1. Provide a mapping from ROS *.srv file to corresponding jrosservices service definition class. Definition class is described by the ServiceDefinition interface.
2. Define all message classes which are part of service definition class defined above (see jrosclient Defining messages guide).

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

Examples

Creating service definition

ROS "add_two_ints" service definition file looks like this:

int64 a
int64 b
---
int64 sum

In ROS2 this file is called "AddTwoInts.srv" and in ROS1 as "TwoInts.srv"

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

For ROS1 we additionally need to obtain md5 sum for request/response messages which in both cases should match service definition. Such md5 sum can be found with "rossrv" command:

Once Java service definition is created, it can be used to run ROS services, as well as to call them.

Call ROS services

In this example we are going to:

• send request from Java to "add_two_ints" ROS service
• wait for the response and print it to the console

How to create and run "add_two_ints" service can be found in:

• ROS2 documentation Writing a simple service and client (C++) or Writing a simple service and client (Python).
• ROS1 documentation rospy overview. For C++ the example can be taken from ros_tutorials package.

Send requests

ROS2

Required Java dependencies:

• jros2client - Java client for ROS2
• jros2services - client for ROS2 Services

Code:

var clientFactory = new JRos2ClientFactory();
var serviceClientFactory = new JRos2ServicesFactory();
try (var client = clientFactory.createClient();
        var serviceClient = serviceClientFactory
            .createClient(client, new AddTwoIntsServiceDefinition(), "add_two_ints")) {
    var request = new AddTwoIntsRequestMessage(3, 2);
    var response = serviceClient.sendRequestAsync(request).get();
    System.out.println(response);
}

ROS1

Required Java dependencies:

• jros1client - Java client for ROS1
• jros1services - client for ROS1 Services

Code:

var clientFactory = new JRos1ClientFactory();
var serviceClientFactory = new JRos1ServiceClientFactory();
try (var client = clientFactory.createClient();
        var serviceClient = serviceClientFactory
            .createClient(client, new AddTwoIntsServiceDefinition(), "add_two_ints")) {
    var request = new AddTwoIntsRequestMessage(3, 2);
    var response = serviceClient.sendRequestAsync(request).get();
    System.out.println(response);
}

Run ROS2 services

In this example we are going to:

• implement "jros_add_two_ints" ROS service in Java
• run "jros_add_two_ints" and execute incoming requests

Code:

var clientFactory = new JRos2ClientFactory();
var serviceClientFactory = new JRos2ServicesFactory();
ServiceHandler<AddTwoIntsRequestMessage, AddTwoIntsResponseMessage> proc =
        request -> {
            System.out.println("Received new request " + request);
            var response = new AddTwoIntsResponseMessage(request.a + request.b);
            System.out.println("Result " + response);
            return response;
        };
try (var client = clientFactory.createClient();
        var service =
                serviceClientFactory.createService(
                        client,
                        new AddTwoIntsServiceDefinition(),
                        "jros_add_two_ints",
                        proc)) {
    service.start();
    System.out.println("Press Enter to stop ROS service...");
    System.in.read();
}

In terminal, use "ros2" command to send requests to "jros_add_two_ints" Java service:

waiting for service to become available...
requester: making request: example_interfaces.srv.AddTwoInts_Request(a=10, b=1)

response:
example_interfaces.srv.AddTwoInts_Response(sum=11)