All you need to do is include any websocket library into your Java project.
I use the Tyrus implementation. https://java.net/projects/tyrus
as an example I implemented a small programm that promt for text input and send it to a topic in ros as std_msgs/String
package myPack;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URI;
import javax.websocket.ContainerProvider;
import javax.websocket.DeploymentException;
import javax.websocket.EncodeException;
import javax.websocket.Session;
import javax.websocket.WebSocketContainer;
import org.json.JSONException;
public class App {
public Session session;
public static MyClient myClient = new MyClient();
protected void start()
{
WebSocketContainer container = ContainerProvider.getWebSocketContainer();
String uri = "ws://localhost:9090";
System.out.println("Connecting to " + uri);
try {
session = container.connectToServer(myClient, URI.create(uri));
} catch (DeploymentException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
public static void main(String args[]) throws JSONException, EncodeException, IOException{
App client = new App();
client.start();
//myClient.subscribe("/face_detection","std_msgs/String");
//myClient.subscribe("/face_detection","std_msgs/String");
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String input = "";
try {
do{
input = br.readLine();
if(!input.equals("exit")){
myClient.publish("/speech",input);
}
}while(!input.equals("exit"));
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
And the class myclient
package myPack;
import java.io.IOException;
import javax.websocket.ClientEndpoint;
import javax.websocket.EncodeException;
import javax.websocket.OnError;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import org.json.JSONException;
import org.json.JSONObject;
@ClientEndpoint
public class MyClient {
Session _session;
JSONObject _message = new JSONObject();
JSONObject _messageData = new JSONObject();
@OnOpen
public void onOpen(Session session) throws JSONException, IOException, EncodeException {
_session = session;
System.out.println("Connected to endpoint: " + session.getBasicRemote());
}
@OnMessage
public void onMessage(String message) throws JSONException, IOException, EncodeException {
_message = new JSONObject(message);
System.out.println((_message.getJSONObject("msg")).getString("data"));
switch((_message.getJSONObject("msg")).getString("data")){
case "FaceAppeared":
publish("/speech","Hello");
break;
case "FaceDisappeared":
publish("/speech","See you");
break;
}
}
@OnError
public void onError(Throwable t) {
t.printStackTrace();
}
public void subscribe(String topic,String type) throws JSONException, IOException, EncodeException {
_message = new JSONObject();
_message.put("op", "subscribe");
_message.put("topic", topic);
_message.put("type", type);
_session.getBasicRemote().sendObject(_message);
}
public void publish(String topic,String messageData) throws JSONException, IOException, EncodeException {
_message = new JSONObject();
_messageData = new JSONObject();
_message.put("op", "publish");
_messageData.put("linear",messageData);
_message.put("msg",_messageData);
_message.put("topic", topic);
_session.getBasicRemote().sendObject(_message);
System.out.println("Send Message "+_message);
}
}
The method onMessage is always called when a topic that your java programm subscribed for through rosbridge is sending something. You can then check first from what topic it came and what to do (in my case I just checked the content of the message, sent when a face appears or disappears from the webcam field of view)
To publish something from your java programm you just use the publish function that I added to the class.
Of course don't forget to start the rosbridge server first.
