ros

Interface RosListenDelegate

public interface RosListenDelegate

This is a delegate interface for handling ros topic subscriptions. The receive(com.fasterxml.jackson.databind.JsonNode, String) is called every time the topic with which this delegate is associated has a new message published. The JSON data, given as a JsonNode, has four top-level fields:

op: what kind of operation it was; should always be "publish"

topic: to which topic the message was published

type: the ROS message type of the topic

msg: the provided ros message in JSON format. This the primary field you will work with.

There are generally two ways you can parse the message into a more usable Java object. The first involves manually iterating through the JSON fields of the msg. For example, for a geometry_msgs/Twist message, you can get out the linear x value as follows:

double x = data.get("msg").get("linear").get("x").asDouble();

(If an element is na array, JSON methods exist for handling it such as JsonNode.get(int) and JsonNode.size()). The the other way is to let the Jackson library unpack it into a JavaBean. The MessageUnpacker class further streamlines this process. See its documentation for more information.

Author:

James MacGlashan.

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static class	RosListenDelegate.LegacyFormat A class for easy conversion to the legacy java_rosbridge receive(com.fasterxml.jackson.databind.JsonNode, String) message format that presented the JSON data in a Map from String to Object instances in which the values were ether primitives, Map objects themselves, or List objects.

Method Summary

Modifier and Type	Method and Description
void	receive(com.fasterxml.jackson.databind.JsonNode data, String stringRep) Receives a new published message to a subscribed topic.

Method Detail

receive

void receive(com.fasterxml.jackson.databind.JsonNode data,
             String stringRep)

Receives a new published message to a subscribed topic. The JSON data, given as a JsonNode, has four top-level fields:

op: what kind of operation it was; should always be "publish"

topic: to which topic the message was published

type: the ROS message type of the topic

msg: the provided ros message in JSON format. This the primary field you will work with.

This method also receives the full string representation of the received JSON message from ROSBridge.

Parameters:

data - the JsonNode containing the JSON data received.

stringRep - the string representation of the JSON object.