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| <div class="docbook"><div class="navheader"><table summary="Navigation header" width="100%"><tr><th align="center" colspan="3">4.6. Exchanges</th></tr><tr><td align="left" width="20%"><a accesskey="p" href="Java-Broker-Concepts-Virtualhosts.html">Prev</a> </td><th align="center" width="60%">Chapter 4. Concepts</th><td align="right" width="20%"> <a accesskey="n" href="Java-Broker-Concepts-Queues.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="Java-Broker-Concepts-Exchanges"></a>4.6. Exchanges</h2></div></div></div><p>An <span class="emphasis"><em>Exchange</em></span> is a named entity within the <span class="emphasis"><em>Virtualhost</em></span> which receives |
| messages from producers and routes them to matching <span class="emphasis"><em>Queue</em></span>s within the <span class="emphasis"><em>Virtualhost</em></span>.</p><p> |
| When using AMQP 0-8, 0-9, 0-9-1, or 0-10, the exchange is the only way ingressing a message into the virtualhost. When using AMQP |
| 1.0, the application may route messages using an exchange (to take advantage of exchange's routing behaviours), or it may route direcly |
| to a queue (if point to point messaging is required). |
| </p><p>The server provides a set of exchange types with each exchange type implementing a different routing algorithm. For details of how |
| these exchanges types work see <a class="xref" href="Java-Broker-Concepts-Exchanges.html#Java-Broker-Concepts-Exchanges-Types" title="4.6.2. Exchange Types">Section 4.6.2, “Exchange Types”</a> below.</p><p>The server predeclares a number of exchange instances with names starting with "<code class="literal">amq.</code>". These are defined in |
| <a class="xref" href="Java-Broker-Concepts-Exchanges.html#Java-Broker-Concepts-Exchanges-Predeclared" title="4.6.1. Predeclared Exchanges">Section 4.6.1, “Predeclared Exchanges”</a>.</p><p>Applications can make use of the pre-declared exchanges, or they may declare their own. The number of exchanges within a <span class="emphasis"><em>Virtualhost</em></span> is |
| limited only by resource constraints.</p><p>The behaviour when an <span class="emphasis"><em>Exchange</em></span> is unable to route a message to any queue is defined in <a class="xref" href="Java-Broker-Concepts-Exchanges.html#Java-Broker-Concepts-Exchanges-UnroutableMessage" title="4.6.4. Unrouteable Messages">Section 4.6.4, “Unrouteable Messages”</a></p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="Java-Broker-Concepts-Exchanges-Predeclared"></a>4.6.1. Predeclared Exchanges</h3></div></div></div><p>Each <span class="emphasis"><em>Virtualhost</em></span> pre-declares the following exchanges: |
| </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>amq.direct (an instance of a direct exchange)</p></li><li class="listitem"><p>amq.topic (an instance of a topic exchange)</p></li><li class="listitem"><p>amq.fanout (an instance of a fanout exchange)</p></li><li class="listitem"><p>amq.match (an instance of a headers exchange)</p></li></ul></div><p> |
| </p><p>The conceptual "<code class="literal">default exchange</code>" always exists, effectively a special instance of |
| direct exchange which uses the empty string as its name. All queues are automatically bound to it upon their creation |
| using the queue name as the binding key, and unbound upon their deletion. It is not possible to manually add or remove |
| bindings within this exchange.</p><p>Applications may not declare exchanges with names beginning with "<code class="literal">amq.</code>". Such names are reserved for system use.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="Java-Broker-Concepts-Exchanges-Types"></a>4.6.2. Exchange Types</h3></div></div></div><p> |
| The following Exchange types are supported. |
| </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>Direct</p></li><li class="listitem"><p>Topic</p></li><li class="listitem"><p>Fanout</p></li><li class="listitem"><p>Headers</p></li></ul></div><p> |
| These exchange types are described in the following sub-sections.</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="Java-Broker-Concepts-Exchanges-Types-Direct"></a>4.6.2.1. Direct</h4></div></div></div><p>The direct exchange type routes messages to queues based on an exact match between |
| the routing key of the message, and the binding key used to bind the queue to the exchange. Additional |
| filter rules may be specified using a <a class="link" href="Java-Broker-Concepts-Exchanges.html#Java-Broker-Concepts-Exchanges-BindingArguments-JMSSelector" title="4.6.3.1. JMS Selector"> |
| binding argument specifying a JMS message selector</a>. |
| </p><p>This exchange type is often used to implement point to point messaging. When used in this manner, the normal |
| convention is that the binding key matches the name of the queue. It is also possible to use this exchange type |
| for multi-cast, in this case the same binding key is associated with many queues.</p><div class="figure"><a id="d0e637"></a><p class="title"><strong>Figure 4.4. Direct exchange</strong></p><div class="figure-contents"><div class="mediaobject"><img alt="Direct exchange" src="images/Exchange-Direct.png" /></div></div></div><br class="figure-break" /><p>The figure above illustrates the operation of direct exchange type. The yellow messages published with the routing key |
| "<code class="literal">myqueue</code>" match the binding key corresponding to queue "<code class="literal">myqueue</code>" and so are routed there. The red |
| messages published with the routing key "<code class="literal">foo</code>" match two bindings in the table so a copy of the message is |
| routed to both the "<code class="literal">bar1</code>" and "<code class="literal">bar2</code>" queues.</p><p>The routing key of the blue message matches no binding keys, so the message is unroutable. It is handled as described |
| in <a class="xref" href="Java-Broker-Concepts-Exchanges.html#Java-Broker-Concepts-Exchanges-UnroutableMessage" title="4.6.4. Unrouteable Messages">Section 4.6.4, “Unrouteable Messages”</a>.</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="Java-Broker-Concepts-Exchanges-Types-Topic"></a>4.6.2.2. Topic</h4></div></div></div><p>This exchange type is used to support the classic publish/subscribe paradigm.</p><p>The topic exchange is capable of routing messages to queues based on wildcard matches between the routing key and the |
| binding key pattern defined by the queue binding. Routing keys are formed from one or more words, with each word delimited |
| by a full-stop (.). The pattern matching characters are the * and # symbols. The * symbol matches a single word and the # |
| symbol matches zero or more words.</p><p>Additional filter rules may be specified using a <a class="link" href="Java-Broker-Concepts-Exchanges.html#Java-Broker-Concepts-Exchanges-BindingArguments-JMSSelector" title="4.6.3.1. JMS Selector"> |
| binding argument specifying a JMS message selector</a>.</p><p>The following three figures help explain how the topic exchange functions.</p><p /><div class="figure"><a id="d0e679"></a><p class="title"><strong>Figure 4.5. Topic exchange - exact match on topic name</strong></p><div class="figure-contents"><div class="mediaobject"><img alt="Topic exchange - exact match on topic name" src="images/Exchange-Topic.png" /></div></div></div><br class="figure-break" /><p>The figure above illustrates publishing messages with routing key "<code class="literal">weather</code>". The exchange routes each |
| message to every bound queue whose binding key matches the routing key.</p><p>In the case illustrated, this means that each subscriber's queue receives every yellow message.</p><div class="figure"><a id="d0e692"></a><p class="title"><strong>Figure 4.6. Topic exchange - matching on hierarchical topic patterns</strong></p><div class="figure-contents"><div class="mediaobject"><img alt="Topic exchange - matching on hierarchical topic patterns" src="images/Exchange-Topic-Hierarchical.png" /></div></div></div><br class="figure-break" /><p>The figure above illustrates publishing messages with hierarchical routing keys. As before, the exchange routes each |
| message to every bound queue whose binding key matches the routing key but as the binding keys contain wildcards, the |
| wildcard rules described above apply.</p><p>In the case illustrated, <code class="literal">sub1</code> has received the red and green message as "<code class="literal">news.uk</code>" and "<code class="literal">news.de</code>" |
| match binding key "<code class="literal">news.#</code>". The red message has also gone to <code class="literal">sub2</code> and <code class="literal">sub3</code> as it's routing key |
| is matched exactly by "<code class="literal">news.uk</code>" and by "<code class="literal">*.uk</code>".</p><p>The routing key of the yellow message matches no binding keys, so the message is unroutable. It is handled as described |
| in <a class="xref" href="Java-Broker-Concepts-Exchanges.html#Java-Broker-Concepts-Exchanges-UnroutableMessage" title="4.6.4. Unrouteable Messages">Section 4.6.4, “Unrouteable Messages”</a>.</p><div class="figure"><a id="d0e730"></a><p class="title"><strong>Figure 4.7. Topic exchange - matching on JMS message selector</strong></p><div class="figure-contents"><div class="mediaobject"><img alt="Topic exchange - matching on JMS message selector" src="images/Exchange-Topic-JMSSelector.png" /></div></div></div><br class="figure-break" /><p>The figure above illustrates messages with properties published with routing key "<code class="literal">shipping</code>".</p><p>As before, the exchange routes each message to every bound queue whose binding key matches the routing key but as a JMS selector |
| argument has been specified, the expression is evaluated against each matching message. Only messages whose message header values or properties |
| match the expression are routed to the queue.</p><p>In the case illustrated, <code class="literal">sub1</code> has received the yellow and blue message as their property "<code class="literal">area</code>" |
| cause expression "<code class="literal">area in ('Forties', 'Cromarty')</code>" to evaluate true. Similarly, the yellow message has also gone to |
| <code class="literal">gale_alert</code> as its property "<code class="literal">speed</code>" causes expression "<code class="literal">speed > 7 and speed < 10</code>" |
| to evaluate true.</p><p>The properties of purple message cause no expressions to evaluate true, so the message is unroutable. It is handled as described in |
| <a class="xref" href="Java-Broker-Concepts-Exchanges.html#Java-Broker-Concepts-Exchanges-UnroutableMessage" title="4.6.4. Unrouteable Messages">Section 4.6.4, “Unrouteable Messages”</a>.</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="Java-Broker-Concepts-Exchanges-Types-Fanout"></a>4.6.2.3. Fanout</h4></div></div></div><p>The fanout exchange type routes messages to all queues bound to the exchange, regardless of the message's routing key.</p><p>Filter rules may be specified using a <a class="link" href="Java-Broker-Concepts-Exchanges.html#Java-Broker-Concepts-Exchanges-BindingArguments-JMSSelector" title="4.6.3.1. JMS Selector"> |
| binding argument specifying a JMS message selector</a>.</p><div class="figure"><a id="d0e777"></a><p class="title"><strong>Figure 4.8. Fanout exchange</strong></p><div class="figure-contents"><div class="mediaobject"><img alt="Fanout exchange" src="images/Exchange-Fanout.png" /></div></div></div><br class="figure-break" /></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="Java-Broker-Concepts-Exchanges-Types-Headers"></a>4.6.2.4. Headers</h4></div></div></div><p>The headers exchange type routes messages to queues based on header properties within the message. The message is passed to |
| a queue if the header properties of the message satisfy the <a class="link" href="Java-Broker-Concepts-Exchanges.html#Java-Broker-Concepts-Exchanges-BindingArguments-x-match" title="4.6.3.2. x-match"> |
| x-match expression</a> specified by the binding arguments with which the queue was bound. |
| </p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="Java-Broker-Concepts-Exchanges-BindingArguments"></a>4.6.3. Binding Arguments</h3></div></div></div><p>Binding arguments are used by certain exchange types to further filter messages.</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="Java-Broker-Concepts-Exchanges-BindingArguments-JMSSelector"></a>4.6.3.1. JMS Selector</h4></div></div></div><p>The binding argument <code class="literal">x-filter-jms-selector</code> specifies a JMS selector conditional expression. The expression |
| is written in terms of message header and message property names. If the expression evaluates to true, the message is routed to the queue. |
| This type of binding argument is understood by exchange types direct, topic and fanout.<a class="footnote" href="#ftn.d0e804" id="d0e804"><sup class="footnote">[4]</sup></a>.</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a id="Java-Broker-Concepts-Exchanges-BindingArguments-x-match"></a>4.6.3.2. x-match</h4></div></div></div><p>The binding argument <code class="literal">x-match</code> is understood by exchange type headers. It can take two values, dictating how the |
| rest of the name value pairs are treated during matching.</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p><code class="literal">all</code> implies that all the other pairs must match the headers property of a message for that message to be routed |
| (i.e. an AND match)</p></li><li class="listitem"><p><code class="literal">any</code> implies that the message should be routed if any of the fields in the headers property match one of the |
| fields in the arguments table (i.e. an OR match)</p></li></ul></div><p>A field in the bind arguments matches a field in the message if either the field in the bind arguments has no value and a field of the |
| same name is present in the message headers or if the field in the bind arguments has a value and a field of the same name exists in the |
| message headers and has that same value.</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="Java-Broker-Concepts-Exchanges-UnroutableMessage"></a>4.6.4. Unrouteable Messages</h3></div></div></div><p>If an exchange is unable to route a message to any queues, the Broker will: |
| </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>If using the AMQP 1.0 protocol, and an alternate binding has been set on the exchange, the message is routed to the alternate. |
| If the message is still unroutable after considering the alternate binding, the message is discarded unless the sending link has requested the |
| <code class="literal">REJECT_UNROUTABLE</code> target capability, or the Exchange has its <code class="literal">unroutableMessageBehaviour</code> attribute set to |
| <code class="literal">REJECT</code>.</p></li><li class="listitem"><p>If using the AMQP 0-10 protocol, and an alternate binding has been set on the exchange, the message is routed to the alternate. |
| If the message is still unroutable after considering the alternate binding,the message is discarded.</p></li><li class="listitem"><p>If using AMQP protocols 0-8..0-9-1, and the publisher set the mandatory flag and the<a class="link" href="Java-Broker-Runtime-Close-Connection-When-No-Route.html" title="9.5. Closing client connections on unroutable mandatory messages"> |
| close when no route</a> feature did not close the connection, the message is returned to the Producer.</p></li><li class="listitem"><p>Otherwise, the message is discarded.</p></li></ul></div><p> |
| </p></div><div class="footnotes"><br /><hr style="width:100; text-align:left;margin-left: 0" /><div class="footnote" id="ftn.d0e804"><p><a class="para" href="#d0e804"><sup class="para">[4] </sup></a> |
| This is a Qpid specific extension.</p></div></div></div><div class="navfooter"><hr /><table summary="Navigation footer" width="100%"><tr><td align="left" width="40%"><a accesskey="p" href="Java-Broker-Concepts-Virtualhosts.html">Prev</a> </td><td align="center" width="20%"><a accesskey="u" href="Java-Broker-Concepts.html">Up</a></td><td align="right" width="40%"> <a accesskey="n" href="Java-Broker-Concepts-Queues.html">Next</a></td></tr><tr><td align="left" valign="top" width="40%">4.5. Virtualhosts </td><td align="center" width="20%"><a accesskey="h" href="Apache-Qpid-Broker-J-Book.html">Home</a></td><td align="right" valign="top" width="40%"> 4.7. Queues</td></tr></table></div></div> |
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