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<h2 class="title">Publish/Subscribe and subscriptions to topics</h2>
<p class="para">
SAM allows messages to be sent either to queues or, for WebSphere MQ
and WPM, to publish/subscribe topics.
A topic destination is specified to SAM in the usual way, i.e. in the
form 'topic://fred', rather than the form 'queue://AQUEUE' used for
point to point operation. To use publish/subscribe it is simply
necessary to specify the correct broker name on the SAMConnect
"connect" call and the desired topic in the destination argument to
the SAMConnect "send" and "receive" calls. The PHP interface is
otherwise identical to the point to point model.
</p>
<p class="para">
By default, SAM creates non-durable subscriptions when using
publish/subscribe. This means that if a client application is
inactive when messages are published to a topic, then it will not
receive them when it subsequently restarted. SAM does also allow
durable subscriptions to be made to topics when using WPM or WebSphere
MQ publish/subscribe. The purpose of these subscriptions is to allow
data to be received by a client application even if that client was not
active at the time the data was published.
</p>
<p class="para">
Durable subscriptions are specified by using the SAMConnect "subscribe"
call. This method takes the destination topic as an input parameter and
returns a subscription identifier that may be used on subsequent
"receive" calls. When the subscription is no longer required the
SAMConnection "unsubscribe" method should be used to delete the
subscription.
</p>
<p class="para">
<div class="example" id="example-4509">
<p><strong>Example #1 Creating a durable subscription to a topic</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /><br />$subName </span><span style="color: #007700">= </span><span style="color: #0000BB">$conn</span><span style="color: #007700">-></span><span style="color: #0000BB">subscribe</span><span style="color: #007700">(</span><span style="color: #DD0000">'topic://A'</span><span style="color: #007700">);<br /><br />if (!</span><span style="color: #0000BB">$subName</span><span style="color: #007700">) {<br /> echo </span><span style="color: #DD0000">"Subscribe failed"</span><span style="color: #007700">;<br />} else {<br /> </span><span style="color: #FF8000"># Subscribe was OK<br /> // ...<br /></span><span style="color: #007700">}<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">
<div class="example" id="example-4510">
<p><strong>Example #2 Subscribing to a topic using a WebSphere Platform Messaging (WPM) server</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$conn </span><span style="color: #007700">= new </span><span style="color: #0000BB">SAMConnection</span><span style="color: #007700">();<br /></span><span style="color: #FF8000">// Note: For pub/sub on WPM, when connecting the name of a messaging engine<br />// to hold the durable subscription (SAM_WPM_DUR_SUB_HOME) must be specified.<br /></span><span style="color: #0000BB">$conn</span><span style="color: #007700">-></span><span style="color: #0000BB">connect</span><span style="color: #007700">(</span><span style="color: #0000BB">SAM_WMQ</span><span style="color: #007700">, array(</span><span style="color: #0000BB">SAM_ENDPOINTS </span><span style="color: #007700">=> </span><span style="color: #DD0000">'localhost:7278:BootstrapBasicMessaging'</span><span style="color: #007700">,<br /> </span><span style="color: #0000BB">SAM_BUS </span><span style="color: #007700">=> </span><span style="color: #DD0000">'Bus1'</span><span style="color: #007700">,<br /> </span><span style="color: #0000BB">SAM_TARGETCHAIN </span><span style="color: #007700">=> </span><span style="color: #DD0000">'InboundBasicMessaging'</span><span style="color: #007700">,<br /> </span><span style="color: #0000BB">SAM_WPM_DUR_SUB_HOME </span><span style="color: #007700">=> </span><span style="color: #DD0000">'MyMachineNode01.server1-Bus1'</span><span style="color: #007700">));<br /><br /></span><span style="color: #0000BB">$subName </span><span style="color: #007700">= </span><span style="color: #0000BB">$conn</span><span style="color: #007700">-></span><span style="color: #0000BB">subscribe</span><span style="color: #007700">(</span><span style="color: #DD0000">'topic://A'</span><span style="color: #007700">);<br /><br />if (!</span><span style="color: #0000BB">$subName</span><span style="color: #007700">) {<br /> echo </span><span style="color: #DD0000">"Subscribe failed"</span><span style="color: #007700">;<br />} else {<br /> </span><span style="color: #FF8000"># Subscribe was OK<br /> // ...<br /></span><span style="color: #007700">}<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">
<div class="example" id="example-4511">
<p><strong>Example #3 Receiving published data using a durable subscription</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /><br />$msg </span><span style="color: #007700">= </span><span style="color: #0000BB">$conn</span><span style="color: #007700">-></span><span style="color: #0000BB">receive</span><span style="color: #007700">(</span><span style="color: #0000BB">$subName</span><span style="color: #007700">);<br />if (</span><span style="color: #0000BB">$msg</span><span style="color: #007700">) {<br /> echo </span><span style="color: #DD0000">"Received a message OK"</span><span style="color: #007700">;<br />} else {<br /> echo </span><span style="color: #DD0000">"The receive failed"</span><span style="color: #007700">;<br />}<br /><br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">
<div class="example" id="example-4512">
<p><strong>Example #4 Deleting a durable subscription to a topic</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /><br /></span><span style="color: #007700">if (!</span><span style="color: #0000BB">$conn</span><span style="color: #007700">-></span><span style="color: #0000BB">unsubscribe</span><span style="color: #007700">(</span><span style="color: #0000BB">$subName</span><span style="color: #007700">)) {<br /> echo </span><span style="color: #DD0000">"Unsubscribe failed"</span><span style="color: #007700">;<br />}<br /><br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
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