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
Weathertopic, either by creating the topic if it does not exist, or retrieving the proxy for the existing topic. - Obtain a proxy for the
Weathertopic'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[])
{
...
auto obj = communicator->stringToProxy("IceStorm/TopicManager:tcp -p 9999");
auto topicManager = Ice::checkedCast<IceStorm::TopicManagerPrx>(obj);
std::shared_ptr<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.
}
}
}
auto pub = topic->getPublisher()->ice_oneway();
auto monitor = Ice::uncheckedCast<MonitorPrx>(pub);
while(true)
{
auto m = getMeasurement();
monitor->report(m);
}
...
}
#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:
std::shared_ptr<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.
}
}
}
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.)
auto pub = topic->getPublisher()->ice_oneway(); auto monitor = Ice::uncheckedCast<MonitorPrx>(pub);
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)
{
auto m = getMeasurement();
monitor->report(m);
}
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)
{
...
com.zeroc.Ice.ObjectPrx obj = communicator.stringToProxy("IceStorm/TopicManager:tcp -p 9999");
com.zeroc.IceStorm.TopicManagerPrx topicManager = com.zeroc.IceStorm.TopicManagerPrx.checkedCast(obj);
IceStorm.TopicPrx topic = null;
while(topic == null)
{
try
{
topic = topicManager.retrieve("Weather");
}
catch(com.zeroc.IceStorm.NoSuchTopic ex)
{
try
{
topic = topicManager.create("Weather");
}
catch(com.zeroc.IceStorm.TopicExists ex)
{
// Another client created the topic.
}
}
}
com.zeroc.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:
com.zeroc.IceStorm.TopicPrx topic = null;
while(topic == null)
{
try
{
topic = topicManager.retrieve("Weather");
}
catch(com.zeroc.IceStorm.NoSuchTopic ex)
{
try
{
topic = topicManager.create("Weather");
}
catch(com.zeroc.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:
com.zeroc.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);
}