<div class="wiki-content maincontent"><h2>JMS Selectors</h2>

<p>Selectors are a way of attaching a filter to a subscription to perform content based routing. Selectors are defined using SQL 92 syntax and typically apply to message headers; whether the standard properties available on a JMS message or custom headers you can add via the JMS code.</p>

<p>Here is an example</p>

<structured-macro ac:macro-id="f3768a53-c6dc-48df-b415-351bc7ffc0ba" ac:name="code" ac:schema-version="1"><plain-text-body>
JMSType = 'car' AND color = 'blue' AND weight &gt; 2500
</plain-text-body></structured-macro>

<p>For more documentation on the detail of selectors see the reference on <a shape="rect" href="http://java.sun.com/j2ee/1.4/docs/api/javax/jms/Message.html">javax.jmx.Message</a>. <br clear="none">
ActiveMQ supports some JMS defined properties, as well as some ActiveMQ ones - see <link><page ri:content-title="ActiveMQ Message Properties"></page><link-body>message properies </link-body></link> - that the selector can use.</p>

<h3>Using XPath to filter messages</h3>

<p>Apache ActiveMQ also supports XPath based selectors when working with messages containing XML bodies. To use an XPath selector use the following syntax</p>

<structured-macro ac:macro-id="518e2e91-77e2-4043-8eb8-a0cb12d232f8" ac:name="code" ac:schema-version="1"><plain-text-body>
XPATH '//title[@lang=''eng'']'
</plain-text-body></structured-macro>

<structured-macro ac:macro-id="a2264760-f437-4e30-aef0-a443c1339472" ac:name="tip" ac:schema-version="1"><parameter ac:name="title">Xalan dependency</parameter><rich-text-body>
<p>XPath support requires <a shape="rect" href="http://xalan.apache.org/index.html">Xalan</a> which is not part of the distribution. The Xalan jars needs to be manually added to lib directory or pulled into your app via maven </p>
<structured-macro ac:macro-id="50c8144b-97b0-4de2-866f-df74715a9173" ac:name="code" ac:schema-version="1"><plain-text-body>&lt;dependency&gt;
    &lt;groupId&gt;xalan&lt;/groupId&gt;
    &lt;artifactId&gt;xalan&lt;/artifactId&gt;
    &lt;version&gt;2.6.0&lt;/version&gt;
&lt;/dependency&gt;</plain-text-body></structured-macro></rich-text-body></structured-macro>

<h3>String Property Conversions / Selecting Against STOMP messages</h3>

<p>The JMS spec states that a String property should not get converted to a numeric when used in a selector.  So for example, if a message has the 'age' property set to String '21' then the following selector should not match it: 'age &gt; 18'.  Since ActiveMQ support STOMP client which can only send messages with string properties, that restriction is a bit limiting.  If you want your JMS selectors to auto-convert String properties the the appropriate number type, just prefix the the selector with 'convert_string_expressions:'.  If you changed selector in the previous example to be 'convert_string_expressions:age &gt; 18', then it would match the message.</p>
</div>