Custom Messages ROS Java System Example

This is an example ROS system that demonstrates the usage of custom ROS topic messages and custom ROS Service definitions. The example runs completely on Java with no ROS instalation required. The example demonstrates running a roscore and four rosjava ROS nodes that use custom ROS messages using the ROS Java roscore. ROS Java contains a plain java, standalone version of roscore that does not require any ROS instalation to be present.

In this repository, a Topic Publisher, a ROS Topic Subscriber, a ROS Service Server and a Service Client are created using the custom ROS messages. A version of this repository that uses predefined ROS messages only is available here. This repository builds on top of the aforementioned Plain ROS Java System Example.

This example project demonstrates how to do the following programmatically through the ROS Java API:

1. Create and use a reusable java jar library with the generated ROS Java definitions for custom ROS messages
2. Publish and subscribe to a ROS topic that is created with a custom ROS topic message.
3. Create a ROS Service Server and call it from a ROS Service Client that is created with a custom ROS service definition.
4. Create, start and shutdown the Java roscore
5. Create, start and shutdown ROS nodes

This repository also provides an example that demonstrates how to run rosjava with an another roscore. E.g. cpp roscore from ROS noetic.

Project Modules

The 'custom-ros-messages' module

This module creates java library jar with a custom Ros Topic Message and a custom ROS Service definition.
The custom ROS Topic message also demonstrates how to use predefined ROS messages, by using as an example the sensor_msgs/JointState.

The 'ros-app' module

This module uses the custom-ros-messages module to implement a service/client and publisher/subcriber examples.

Requirements

In order to compile and run this project only Java needs to be installed. GIT also makes getting the source very easy. Links are provided for convenience.

• GIT , in order to clone the project repository
• JDK, the project has been developed and tested using JDK 17
• Gradle, is used for project compilation. Installing it is not required. Following the instructions below will automatically download gradle 7.5 and ignore any existing installation.

Quick Instructions for Windows Power Shell

1. Clone the project repository: git clone https://github.com/SpyrosKou/Custom-Messages-ROS-Java-System-Example.git

2. Go into the cloned repository directory: cd .\Custom-Messages-ROS-Java-System-Example\

3. Compile the project and prepare for running: gradlew installDist

4. Build and run in a single command using the gradle application plugin: gradlew run

Quick Instructions for Linux

1. Clone the project repository: git clone https://github.com/SpyrosKou/Custom-Messages-ROS-Java-System-Example.git

2. Go into the cloned repository directory: cd Custom-Messages-ROS-Java-System-Example/

3. Add execute permission to gradlew script: sudo chmod +x gradlew

4. Compile the project and install it locally: gradlew installDist

5. Build and run in a single command using using the gradle application plugin: gradlew run

Using with an existing, external, non-rosjava roscore

It is possible to use rosjava to run rosjava nodes in an environment where a ros system is already running. E.g. a cpp noetic ros instance. An example on how to run rosjava nodes programmatically without starting roscore is provided in MainExternal Note that if a roscore is not running, then this example will not run correctly. In order to use it do the following:

1. Set ROS_MASTER_URI and ROS_IP environment variables. Both these variables are needed. If these environment variables are missing, you will see some errors in step 4 below. The following commands assumes the example and roscore run in 127.0.0.1 aka localhost.
   export ROS_MASTER_URI=http://127.0.0.1:11311
export ROS_IP=http://127.0.0.1:11311

2. Start roscore Run the following: roscore

3. With the roscore already started externaly run MainExternal

4. You can start directly the MainExternal from the gradle by running: ./gradlew runWithExternalRos