The implementation of our weather measurement collector application can be summarized easily:
- Obtain a proxy for the
TopicManager
. This is the primary IceStorm object, used by both publishers and subscribers. - Obtain a proxy for the
Weather
topic, either by creating the topic if it does not exist, or retrieving the proxy for the existing topic. - Obtain a proxy for the
Weather
topic's "publisher object." This proxy is provided for the purpose of publishing messages, and therefore is narrowed to the topic interface (Monitor
). - Collect and report measurements.
We present collector implementations in C++ and Java below.
On this page:
Publisher Example in C++
As usual, our C++ example begins by including the necessary header files. The interesting ones are IceStorm/IceStorm.h
, which is generated from the IceStorm Slice definitions, and Monitor.h
, containing the generated code for our monitor definitions shown above.
#include <Ice/Ice.h> #include <IceStorm/IceStorm.h> #include <Monitor.h> int main(int argc, char* argv[]) { ... Ice::ObjectPrx obj = communicator->stringToProxy("IceStorm/TopicManager:tcp -p 9999"); IceStorm::TopicManagerPrx topicManager = IceStorm::TopicManagerPrx::checkedCast(obj); IceStorm::TopicPrx topic; while (!topic) { try { topic = topicManager->retrieve("Weather"); } catch (const IceStorm::NoSuchTopic&) { try { topic = topicManager->create("Weather"); } catch (const IceStorm::TopicExists&) { // Another client created the topic. } } } Ice::ObjectPrx pub = topic->getPublisher()->ice_oneway(); MonitorPrx monitor = MonitorPrx::uncheckedCast(pub); while (true) { Measurement m = getMeasurement(); monitor->report(m); } ... }
Note that this example assumes that IceStorm uses the instance name IceStorm
. The actual instance name may differ, and you need to use it as the category when calling stringToProxy
.
After obtaining a proxy for the topic manager, the collector attempts to retrieve the topic. If the topic does not exist yet, the collector receives a NoSuchTopic
exception and then creates the topic:
IceStorm::TopicPrx topic; while(!topic) { try { topic = topicManager->retrieve("Weather"); } catch (const IceStorm::NoSuchTopic&) { try { topic = topicManager->create("Weather"); } catch (const IceStorm::TopicExists&) { // Another client created the topic. } } }
The next step is obtaining a proxy for the publisher object, which the collector narrows to the Monitor
interface. (We create a oneway proxy for the publisher purely for efficiency reasons.)
Ice::ObjectPrx pub = topic->getPublisher()->ice_oneway(); MonitorPrx monitor = MonitorPrx::uncheckedCast(pub);
Finally, the collector enters its main loop, collecting measurements and publishing them via the IceStorm publisher object:
while (true) { Measurement m = getMeasurement(); monitor->report(m); }
Publisher Example in Java
The equivalent Java version is shown below:
public static void main(String[] args) { ... Ice.ObjectPrx obj = communicator.stringToProxy("IceStorm/TopicManager:tcp -p 9999"); IceStorm.TopicManagerPrx topicManager = IceStorm.TopicManagerPrxHelper.checkedCast(obj); IceStorm.TopicPrx topic = null; while (topic == null) { try { topic = topicManager.retrieve("Weather"); } catch (IceStorm.NoSuchTopic ex) { try { topic = topicManager.create("Weather"); } catch (IceStorm.TopicExists ex) { // Another client created the topic. } } } Ice.ObjectPrx pub = topic.getPublisher().ice_oneway(); MonitorPrx monitor = MonitorPrxHelper.uncheckedCast(pub); while (true) { Measurement m = getMeasurement(); monitor.report(m); } ... }
Note that this example assumes that IceStorm uses the instance name IceStorm
. The actual instance name may differ, and you need to use it as the category when calling stringToProxy
.
After obtaining a proxy for the topic manager, the collector attempts to retrieve the topic. If the topic does not exist yet, the collector receives a NoSuchTopic
exception and then creates the topic:
IceStorm.TopicPrx topic = null; while (topic == null) { try { topic = topicManager.retrieve("Weather"); } catch (IceStorm.NoSuchTopic ex) { try { topic = topicManager.create("Weather"); } catch (IceStorm.TopicExists ex) { // Another client created the topic. } } }
The next step is obtaining a proxy for the publisher object, which the collector narrows to the Monitor
interface:
Ice.ObjectPrx pub = topic.getPublisher().ice_oneway(); MonitorPrx monitor = MonitorPrxHelper.uncheckedCast(pub);
Finally, the collector enters its main loop, collecting measurements and publishing them via the IceStorm publisher object:
while (true) { Measurement m = getMeasurement(); monitor.report(m); }