<?xml version="1.0" encoding="UTF-8"?>
<appendix xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="samples"
    xmlns:xlink="http://www.w3.org/1999/xlink">
  <title>Spring Integration Samples</title>

 <section id="samples-introduction">
   <title>Introduction</title>
   <para>
   As of Spring Integration 2.0, the <emphasis>samples</emphasis> are no longer included with the
   Spring Integration distribution. Instead we have switched to a much simpler collaborative model that should promote
   better community participation and, ideally, more contributions. Samples now have a dedicated Git repository and a
   dedicated JIRA Issue Tracking system. Sample development will also have its own lifecycle which is not dependent on the
   lifecycle of the framework releases although the repository will still be tagged with each major release for compatibility
   reasons.
   </para>
   <para>
   The great benefit to the community is that we can now add more samples and make them available to you right away
   without waiting for the next release. Having its own JIRA that is not tied to the the actual
   framework is also a great benefit. You now have a dedicated place to suggest samples as well as report issues with existing
   samples. Or, <emphasis> you may want to submit a sample to us</emphasis>  as an attachment through the JIRA or, better, through
   the collaborative model that Git promotes. If we believe your sample adds value, we
   would be more then glad to add it to the 'samples' repository, properly crediting you as the author.
   </para>
 </section>

 <section id="samples-get">
   <title>Where to get Samples</title>
   <para>
   To monitor samples development and to get more information on the repository you can visit the following
   URL: <link linkend="http://git.springsource.org/spring-integration/samples">http://git.springsource.org/spring-integration/samples</link>
    Since we are using Git as the SCM, we should use the proper terminology as well when it comes to the tasks you need to perform to make
    <emphasis>samples</emphasis> available locally on your machine. For more information on Git SCM please visit their
    website: <link linkend="http://git-scm.com/">http://git-scm.com/</link>
   </para>
   <para>
   CLONE <emphasis>samples</emphasis> repository. (For those unfamiliar with Git, this is somewhat the equivalent of a checkout.)
   </para>
   <para>
   This is the first step you should go through. You must have Git installed on your machine. There are many GUI-based products
   available for many platforms. A simple Google search will help you find them.
    To clone the Spring Integration samples repository, issue the following at the command line:
    <programlisting language="xml"><![CDATA[> mkdir spring-integration-samples
> cd spring-integration-samples
> git clone git://git.springsource.org/spring-integration/samples.git]]></programlisting>
   </para>
   <para>
   That is all you need to do. Now you have cloned the entire samples repository. Since the samples repository is a live
   repository, you might want to perform periodic "pulls" to get new samples as well as updates to the existing samples.
   To get the updates use the git PULL command:
   <programlisting language="xml"><![CDATA[> git pull]]></programlisting>
   </para>
   <para>
   Submit samples or sample requests
   </para>
   <para>
   As mentioned earlier, Spring Integration <emphasis>samples</emphasis> have a dedicated JIRA Issue tracking system.
   To submit new sample requests or to submit an actual sample (as an attachment), please visit our JIRA Issue Tracking system:
   <ulink url="https://jira.springframework.org/browse/INTSAMPLES">https://jira.springframework.org/browse/INTSAMPLES</ulink>.
   </para>
 </section>
 <section id="samples-structure">
   <title>Samples Structure</title>
   <para>
   The structure of the <emphasis>samples</emphasis> changed as well. With plans for more samples we realized that some
   samples have different goals than others. While they all share the common goal of showing you how to apply and work with
   the Spring Integration framework, they also differ in areas where some samples are meant to concentrate on a technical
   use case while others focus on a business use case, and some samples are all about showcasing various techniques that
   could be applied to address certain scenarios (both technical and business). The new categorization of samples will allow us
   to better organize them based on the problem each sample addresses while giving you a simpler way of finding the right sample
   for your needs.
   </para>
   <para>
   Currently there are 4 categories. Within the samples repository each category has its own directory which is named after the
   category name:
   </para>

   <para>
   <emphasis>BASIC (samples/basic)</emphasis>
   </para>
   <para>
   This is a good place to get started. The samples here are technically motivated and demonstrate the bare
     minimum with regard to configuration and code. These should help you to get started quickly by introducing you to the basic concepts,
     API and configuration of Spring Integration as well as Enterprise Integration Patterns (EIP). For example, if you are
     looking for an answer on how to implement and wire a <emphasis>Service Activator</emphasis> to a <emphasis>Message Channel</emphasis>
     or how to use a <emphasis>Messaging Gateway</emphasis> as a facade to your message exchange, or how to get started with using MAIL or
     TCP/UDP modules etc., this would be the right place to find a good sample. The bottom line is this is a good place
     to get started.
   </para>

   <para>
   <emphasis>INTERMEDIATE (samples/intermediate)</emphasis>
   </para>
   <para>
   This category targets developers who are already familiar with the Spring Integration framework (past getting started),
  but need some more guidance while resolving the more advanced technical problems one might deal with
  after switching to a Messaging architecture.
  For example, if you are looking for an answer on how to handle errors in various message exchange
  scenarios or how to properly configure the <emphasis>Aggregator</emphasis> for the situations where some messages
  might not ever arrive for aggregation, or any other issue that goes beyond a basic implementation and configuration
  of a particular component and addresses <emphasis>what else</emphasis> types of problems, this
  would be the right place to find these type of samples.
   </para>

   <para>
   <emphasis>ADVANCED (samples/advanced)</emphasis>
   </para>
   <para>
   This category targets developers who are very familiar with the Spring Integration framework but are looking to
  extend it to address a specific custom need by using Spring Integration's public API.
  For example, if you are looking for samples showing you how to implement a custom <emphasis>Channel</emphasis> or
  <emphasis>Consumer</emphasis> (event-based or polling-based), or you are trying to figure out what is the most appropriate
  way to implement a custom Bean parser on top of the Spring Integration Bean parser hierarchy when implementing your own
  namespace and schema for a custom component, this would be the right place to look.
  Here you can also find samples that will help you with <emphasis>Adapter</emphasis> development. Spring Integration comes
  with an extensive library of adapters to allow you to connect remote systems with the Spring Integration messaging framework.
  However you might have a need to integrate with a system for which the core framework does not provide an adapter.
  So, you may decide to implement your own (and potentially contribute it). This category would include samples showing you how.
   </para>

   <para>
   <emphasis>APPLICATIONS (samples/applications)</emphasis>
   </para>
   <para>
   This category targets developers and architects who have a good understanding of Message-driven architecture and
  EIP, and an above average understanding of Spring and Spring Integration who are looking for samples that
  address a particular <emphasis>business problem</emphasis>. In other words the emphasis of samples in this category
  is <emphasis>business use cases</emphasis> and how they can be solved with a Message-Driven Architecture and Spring Integration
  in particular.
  For example, if you are interested to see how a <emphasis>Loan Broker</emphasis> or <emphasis>Travel Agent</emphasis>
  process could be implemented and automated via Spring Integration, this would be the right place to find these types of samples.
   </para>

   <important>
   <remark>
   Remember: Spring Integration is a community driven framework, therefore community participation is IMPORTANT.
That includes Samples; so, if you can't find what you are looking for, let us know!
   </remark>
   </important>
 </section>
  <section id="samples-impl">
    <title>Samples</title>
     <para>
     Currently Spring Integration comes with quite a few samples and you can only expect more.
     To help you better navigate through them, each sample comes with its own <code>readme.txt</code> file which covers
     several details about the sample (e.g., what EIP patterns it addresses, what problem it is trying to solve, how to run sample etc.).
     However, certain samples require a more detailed and sometimes graphical explanation. In this section you'll
     find details on samples that we believe require special attention.
     </para>
      <section id="samples-loan-broker">
        <title>Loan Broker</title>
        <para>
       In this section, we will review the <emphasis>Loan Broker</emphasis> sample application that is included in the
       Spring Integration samples. This sample is inspired by one of the samples featured in Gregor
       Hohpe and Bobby Woolf's book, <ulink url="http://www.eaipatterns.com">Enterprise Integration Patterns</ulink>.
        </para>
        <para>The diagram below represents the entire process</para>
        <para>
        <mediaobject>
          <imageobject role="fo">
              <imagedata fileref="images/loan-broker-eip.png" format="PNG" align="center" scalefit="1" width="100%" contentdepth="100%" />
          </imageobject>
          <imageobject role="html">
              <imagedata fileref="images/loan-broker-eip.png" format="PNG" align="center"/>
          </imageobject>
        </mediaobject>
      </para>
      <para>Now lets look at this process in more detail</para>
      <para>
      At the core of an EIP architecture are the very simple yet powerful concepts of Pipes and Filters, and of course: Messages.
      Endpoints (Filters) are connected with one another via Channels (Pipes). The producing endpoint sends Message to the Channel,
      and the Message is retrieved
      by the Consuming endpoint.  This architecture is meant to define various mechanisms that describe HOW information is exchanged between
      the endpoints, without any awareness of WHAT those endpoints are or what information they are exchanging. Thus, it provides for a very loosely
      coupled and flexible collaboration model while also decoupling Integration concerns from Business concerns. EIP extends this architecture
      by further defining:
        <itemizedlist>
            <listitem>
              <para>The types of pipes (Point-to-Point Channel, Publish-Subscribe Channel, Channel Adapter, etc.)</para>
            </listitem>

            <listitem>
              <para>The core filters and patterns around how filters collaborate with pipes
              (Message Router, Splitters and Aggregators, various Message Transformation patterns, etc.)</para>
            </listitem>
          </itemizedlist>
      </para>
      <para>
      The details and variations of this use case are very nicely described in Chapter 9 of the EIP Book, but here is the brief summary;
      A Consumer while shopping for the best Loan Quote(s) subscribes to the services of a Loan Broker, which handles details such as:
      <itemizedlist>
            <listitem>
              <para>Consumer pre-screening (e.g., obtain and review the consumer's Credit history)</para>
            </listitem>

            <listitem>
              <para>Determine the most appropriate Banks (e.g., based on consumer's credit history/score)</para>
            </listitem>

             <listitem>
              <para>Send a Loan quote request to each selected Bank</para>
            </listitem>
            <listitem>
              <para>Collect responses from each Bank</para>
            </listitem>
            <listitem>
              <para>Filter responses and determine the best quote(s), based on consumer's requirements.</para>
            </listitem>
             <listitem>
              <para>Pass the Loan quote(s) back to the consumer.</para>
            </listitem>
      </itemizedlist>
      </para>
      <para>
      Obviously the real process of obtaining a loan quote is a bit more complex, but since our goal here is to demonstrate how
      Enterprise Integration Patterns are realized and implemented within SI, the use case has been simplified to concentrate only on
       the Integration aspects of the process. It is not an attempt to give you an advice in consumer finances.
      </para>
      <para>
      As you can see, by hiring a Loan Broker, the consumer is isolated from the details of the Loan Broker's operations, and each Loan Broker's
      operations may defer from one another to maintain competitive advantage, so whatever we assemble/implement must be flexible so any changes
      could be introduced quickly and painlessly.
        Speaking of change, the Loan Broker sample does not actually talk to any 'imaginary' Banks or Credit bureaus. Those services are stubbed out.
        Our goal here is to assemble, orchestrate and test the integration aspect of the process as a whole. Only then can we start thinking about
        wiring such process to the real services. At that time the assembled process and its configuration will not change regardless of the number
        of Banks a particular Loan Broker is dealing with, or the type of communication media (or protocols) used (JMS, WS, TCP, etc.)
        to communicate with these Banks.
      </para>
      <para> <emphasis>DESIGN</emphasis> </para>
      <para>
      As you analyze the 6 requirements above you'll quickly see that they all fall into the category of Integration concerns.
      For example, in the consumer pre-screening step we need to gather additional information about the consumer and the consumer's desires
      and enrich the loan request with additional meta information. We then have to filter such information to select the most appropriate list of
      Banks, and so on. Enrich, filter, select – these are all integration concerns for which EIP defines a solution in the form of patterns.
      SI provides an implementation of these patterns.
      </para>
      <para><emphasis>Messaging Gateway</emphasis>
      <mediaobject>
          <imageobject role="fo">
              <imagedata fileref="images/gateway.jpg" format="JPG" align="center"/>
          </imageobject>
          <imageobject role="html">
              <imagedata fileref="images/gateway.jpg" format="JPG" align="center"/>
          </imageobject>
        </mediaobject>
      </para>
      <para>
      The <emphasis>Messaging Gateway</emphasis> pattern provides a simple mechanism to access messaging systems, including our Loan Broker.
      In SI you define the <emphasis>Gateway</emphasis> as a Plain Old Java Interface (no need to provide an implementation), configure it via the
      XML <emphasis>&lt;gateway&gt;</emphasis> element or via annotation and use it as any other Spring bean. SI will take care of
      delegating and mapping method invocations to the Messaging infrastructure by generating a <emphasis>Message</emphasis> (payload is mapped to an
      input parameter of the method) and sending it to the designated channel.
      <programlisting language="xml"><![CDATA[<gateway id="loanBrokerGateway"
  default-request-channel="loanBrokerPreProcessingChannel"
  service-interface="org.springframework.integration.samples.loanbroker.LoanBrokerGateway">
  <method name="getBestLoanQuote">
    <header name="RESPONSE_TYPE" value="BEST"/>
  </method>
</gateway>]]></programlisting>
      </para>
      <para>
      Our current <emphasis>Gateway</emphasis> provides two methods that could be invoked. One that will return the best single quote and another one that
      will return all quotes. Somehow downstream we need to know what type of reply the caller is looking for. The best way to achieve
      this in Messaging architecture is to enrich the content of the message with some meta-data describing your intentions.
      <emphasis>Content Enricher</emphasis> is one of the patterns that addresses this and although Spring Integration does provide a
      separate configuration element to enrich Message Headers with arbitrary data (we'll see it later), as a convenience, since
      <emphasis>Gateway</emphasis> element is responsible to construct the initial <emphasis>Message</emphasis> it provides embedded
      capability to enrich the newly created <emphasis>Message</emphasis> with arbitrary <emphasis>Message Headers</emphasis>. In our
      example we are adding header RESPONSE_TYPE with value 'BEST'' whenever the getBestQuote() method is invoked. For other method
      we are not adding any header. Now we can check downstream for an existence of this header and based on its presence and its value
      we can determine what type of reply the caller is looking for.
      </para>

      <para>
      Based on the use case we also know there are some pre-screening steps that needs to be performed such as getting and evaluating the consumer's
      credit score, simply because some premiere Banks will only typically accept quote requests from consumers that meet a minimum credit
      score requirement. So it would be nice if the <emphasis>Message</emphasis> would be enriched with such information before it is forwarded
      to the Banks. It would also be nice if when several processes needs to be completed to provide such meta-information, those
      processes could be grouped in a single unit. In our use case we need to determine credit score and based on the credit score and some
      rule select a list of <emphasis>Message Channels</emphasis> (Bank Channels) we will sent quote request to.
      </para>
      <para><emphasis>Composed Message Processor</emphasis> </para>
      <para>
      The <emphasis>Composed Message Processor</emphasis> pattern describes rules around building endpoints that maintain control over message flow which
      consists of multiple message processors. In Sprig Integration <emphasis>Composed Message Processor</emphasis> pattern is implemented via
      <emphasis>&lt;chain&gt;</emphasis> element.
      <mediaobject>
          <imageobject role="fo">
              <imagedata fileref="images/chain.png" format="PNG" align="center"/>
          </imageobject>
          <imageobject role="html">
              <imagedata fileref="images/chain.png" format="PNG" align="center"/>
          </imageobject>
        </mediaobject>
      </para>
      <para>
      As you can see from the above configuration we have a chain with inner header-enricher element which will further enrich the
      content of the <emphasis>Message</emphasis> with the header CREDIT_SCORE and value that will be determined by the call to a
      credit service (simple POJO spring bean identified by 'creditBureau' name) and then it will delegate to the <emphasis>Message Router</emphasis>
      </para>
      <para><emphasis>Message Router</emphasis>
      <mediaobject>
          <imageobject role="fo">
              <imagedata fileref="images/bank-router.jpg" format="JPG" align="center"/>
          </imageobject>
          <imageobject role="html">
              <imagedata fileref="images/bank-router.jpg" format="JPG" align="center"/>
          </imageobject>
        </mediaobject>
      </para>
      <para>
      There are several implementations of the <emphasis>Message Routing</emphasis> pattern available in Spring Integration. Here we are using a
      router that will determine a list of channels based on evaluating an expression (Spring Expression Language) which will look at
      the credit score that was determined is the previous step and will select the list of channels from the Map bean with id 'banks'
      whose values are 'premier' or 'secondary' based o the value of credit score. Once the list of <emphasis>Channels</emphasis> is selected, the
      <emphasis>Message</emphasis> will be routed to those <emphasis>Channels</emphasis>.
      </para>
      <para>
      Now, one last thing the Loan Broker needs to to is to receive the loan quotes form the banks, aggregate them by consumer
      (we don't want to show quotes from one consumer to another), assemble the response based on the consumer's selection criteria
      (single best quote or all quotes) and reply back to the consumer.
      </para>
      <para><emphasis>Message Aggregator</emphasis>
      <mediaobject>
          <imageobject role="fo">
              <imagedata fileref="images/quotes-aggregator.jpg" format="JPG" align="center"/>
          </imageobject>
          <imageobject role="html">
              <imagedata fileref="images/quotes-aggregator.jpg" format="JPG" align="center"/>
          </imageobject>
        </mediaobject>
      </para>

      <para>
      An <emphasis>Aggregator</emphasis> pattern describes an endpoint which groups related <emphasis>Messages</emphasis> into a single
      <emphasis>Message</emphasis>. Criteria and rules can be provided to determine an aggregation and correlation strategy.
      SI provides several implementations of the <emphasis>Aggregator</emphasis> pattern as well as a convenient name-space based configuration.
      <programlisting language="xml"><![CDATA[<aggregator id="quotesAggregator"
      input-channel="quotesAggregationChannel"
      method="aggregateQuotes">
  <beans:bean class="org.springframework.integration.samples.loanbroker.LoanQuoteAggregator"/>
</aggregator>]]></programlisting>
      </para>

      <para>
      Our Loan Broker defines a 'quotesAggregator' bean via the <emphasis>&lt;aggregator&gt;</emphasis> element which provides a default
      aggregation and correlation strategy. The default correlation strategy correlates messages based on the <code>correlationId</code> header
      (see <emphasis>Correlation Identifier</emphasis> pattern). What's interesting is that we never provided the value for this header.
      It was set earlier by the router automatically, when it generated a separate <emphasis>Message</emphasis> for each Bank channel.
      </para>
      <para>
      Once the <emphasis>Messages</emphasis> are correlated they are released to the actual <emphasis>Aggregator</emphasis> implementation.
      Although default <emphasis>Aggregator</emphasis> is provided by SI, its strategy (gather the list of payloads from all
      <emphasis>Messages</emphasis> and construct a new <emphasis>Message</emphasis> with this List as payload) does not satisfy our
      requirement. The reason is that our consumer might require a single best quote or all quotes. To communicate the consumer's
      intention, earlier in the process we set the RESPONSE_TYPE header. Now we have to evaluate this header and return either
      all the quotes (the default aggregation strategy would work) or the best quote (the default aggregation strategy will not work
      because we have to determine which loan quote is the best).
      </para>

      <para>
      Obviously selecting the best quote could be based on complex criteria and would influence the complexity of the aggregator implementation and
      configuration, but for now we are making it simple. If consumer wants the best quote we will select a quote with the lowest interest
      rate. To accomplish that the LoanQuoteAggregator.java will sort all the quotes and return the first one.
      The <classname>LoanQuote.java</classname> implements <interfacename>Comparable</interfacename> which compares quotes based on the rate attribute.
        Once the response <emphasis>Message</emphasis> is created it is sent to the default-reply-channel of the <emphasis>Messaging Gateway</emphasis>
        (thus the consumer) which started the process. Our consumer got the Loan Quote!
      </para>
      <para>Conclusion</para>
      <para>
      As you can see a rather complex process was assembled based on POJO (read existing, legacy), light weight, embeddable messaging
      framework (Spring Integration) with a loosely coupled programming model intended to simplify integration of heterogeneous systems
      without requiring a heavy-weight ESB-like engine or proprietary development and deployment environment, because as a developer you
      should not be porting your Swing or console-based application to an ESB-like server or implementing proprietary interfaces just
      because you have an integration concern.
      </para>
      <para>
      This and other samples in this section are build on top of Enterprise Integration Patterns that meant to describe "building blocks"
      for YOUR solution but not to be solutions in of themselves. Integration concerns exist in all types of applications (server based and not)
      and should not require change in design, testing and deployment strategy if such applications need to integrate with one another.
      </para>
    </section>

    <section id="samples-cafe">
      <title>The Cafe Sample</title>
      <para>
       In this section, we will review a <emphasis>Cafe</emphasis> sample application that is included in the
       Spring Integration samples. This sample is inspired by another sample featured in Gregor
       Hohpe's <ulink url="http://www.eaipatterns.com/ramblings.html">Ramblings</ulink>.
      </para>
      <para>
        The domain is that of a Cafe, and the basic flow is depicted in the following diagram:
      </para>
      <para>
        <mediaobject>
          <imageobject role="fo">
              <imagedata fileref="images/cafe-eip.png" format="PNG" align="center" scalefit="1" width="100%" contentdepth="100%" />
          </imageobject>
          <imageobject role="html">
              <imagedata fileref="images/cafe-eip.png" format="PNG" align="center"/>
          </imageobject>
        </mediaobject>
      </para>
      <para>
        The <classname>Order</classname> object may contain multiple <classname>OrderItems</classname>. Once the order
        is placed, a <emphasis>Splitter</emphasis> will break the composite order message into a single message per
        drink. Each of these is then processed by a <emphasis>Router</emphasis> that determines whether the drink is hot
        or cold (checking the <classname>OrderItem</classname> object's 'isIced' property). The
        <classname>Barista</classname> prepares each drink, but hot and cold drink preparation are handled by two
        distinct methods: 'prepareHotDrink' and 'prepareColdDrink'. The prepared drinks are then sent to the Waiter where
        they are aggregated into a <classname>Delivery</classname> object.
      </para>
      <para>
        Here is the XML configuration:
        <programlisting language="xml"><![CDATA[<?xml version="1.0" encoding="UTF-8"?>
  <beans:beans xmlns="http://www.springframework.org/schema/integration"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xmlns:beans="http://www.springframework.org/schema/beans"
      xmlns:stream="http://www.springframework.org/schema/integration/stream"
      xsi:schemaLocation="http://www.springframework.org/schema/beans
              http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
              http://www.springframework.org/schema/integration
              http://www.springframework.org/schema/integration/spring-integration-2.0.xsd
              http://www.springframework.org/schema/integration/stream
              http://www.springframework.org/schema/integration/stream/spring-integration-stream-2.0.xsd">

      <gateway id="cafe" service-interface="org.springframework.integration.samples.cafe.Cafe"/>

      <channel id="orders"/>
      <splitter input-channel="orders" ref="orderSplitter" method="split" output-channel="drinks"/>

      <channel id="drinks"/>
      <router input-channel="drinks" ref="drinkRouter" method="resolveOrderItemChannel"/>

      <channel id="coldDrinks">
          <queue capacity="10"/>
      </channel>
      <service-activator input-channel="coldDrinks" ref="barista"
                         method="prepareColdDrink" output-channel="preparedDrinks"/>

      <channel id="hotDrinks">
          <queue capacity="10"/>
      </channel>
      <service-activator input-channel="hotDrinks" ref="barista"
                         method="prepareHotDrink" output-channel="preparedDrinks"/>

      <channel id="preparedDrinks"/>
      <aggregator input-channel="preparedDrinks" ref="waiter"
                  method="prepareDelivery" output-channel="deliveries"/>

      <stream:stdout-channel-adapter id="deliveries"/>

      <beans:bean id="orderSplitter"
                  class="org.springframework.integration.samples.cafe.xml.OrderSplitter"/>

      <beans:bean id="drinkRouter"
                  class="org.springframework.integration.samples.cafe.xml.DrinkRouter"/>

      <beans:bean id="barista" class="org.springframework.integration.samples.cafe.xml.Barista"/>

      <beans:bean id="waiter" class="org.springframework.integration.samples.cafe.xml.Waiter"/>

      <poller id="poller" default="true" fixed-rate="1000"/>

  </beans:beans>]]></programlisting>
        As you can see, each Message Endpoint is connected to input and/or output channels. Each endpoint will manage
        its own Lifecycle (by default endpoints start automatically upon initialization - to prevent that add the
        "auto-startup" attribute with a value of "false"). Most importantly, notice that the objects are simple POJOs
        with strongly typed method arguments. For example, here is the Splitter:
        <programlisting language="java"><![CDATA[public class OrderSplitter {

      public List<OrderItem> split(Order order) {
          return order.getItems();
      }
  }]]></programlisting>
      In the case of the Router, the return value does not have to be a <interfacename>MessageChannel</interfacename>
      instance (although it can be). As you see in this example, a String-value representing the channel name is
      returned instead.
      <programlisting language="java"><![CDATA[public class DrinkRouter {

      public String resolveOrderItemChannel(OrderItem orderItem) {
          return (orderItem.isIced()) ? "coldDrinks" : "hotDrinks";
      }
  }]]></programlisting>
      </para>
      <para>
        Now turning back to the XML, you see that there are two &lt;service-activator&gt; elements. Each of these
        is delegating to the same <classname>Barista</classname> instance but different methods: 'prepareHotDrink'
        or 'prepareColdDrink' corresponding to the two channels where order items have been routed.
        <programlisting language="java"><![CDATA[public class Barista {

      private long hotDrinkDelay = 5000;
      private long coldDrinkDelay = 1000;

      private AtomicInteger hotDrinkCounter = new AtomicInteger();
      private AtomicInteger coldDrinkCounter = new AtomicInteger();

      public void setHotDrinkDelay(long hotDrinkDelay) {
          this.hotDrinkDelay = hotDrinkDelay;
      }

      public void setColdDrinkDelay(long coldDrinkDelay) {
          this.coldDrinkDelay = coldDrinkDelay;
      }

      public Drink prepareHotDrink(OrderItem orderItem) {
          try {
              Thread.sleep(this.hotDrinkDelay);
              System.out.println(Thread.currentThread().getName()
                      + " prepared hot drink #" + hotDrinkCounter.incrementAndGet()
                      + " for order #" + orderItem.getOrder().getNumber() + ": " + orderItem);
              return new Drink(orderItem.getOrder().getNumber(), orderItem.getDrinkType(),
                      orderItem.isIced(), orderItem.getShots());
          }
          catch (InterruptedException e) {
              Thread.currentThread().interrupt();
              return null;
          }
      }

      public Drink prepareColdDrink(OrderItem orderItem) {
          try {
              Thread.sleep(this.coldDrinkDelay);
              System.out.println(Thread.currentThread().getName()
                      + " prepared cold drink #" + coldDrinkCounter.incrementAndGet()
                      + " for order #" + orderItem.getOrder().getNumber() + ": " + orderItem);
              return new Drink(orderItem.getOrder().getNumber(), orderItem.getDrinkType(),
                      orderItem.isIced(), orderItem.getShots());
          }
          catch (InterruptedException e) {
              Thread.currentThread().interrupt();
              return null;
          }
      }

  }]]></programlisting>
      </para>
      <para>
        As you can see from the code excerpt above, the barista methods have different delays (the hot drinks take 5
        times as long to prepare). This simulates work being completed at different rates. When the
        <classname>CafeDemo</classname> 'main' method runs, it will loop 100 times sending a single hot drink and a
        single cold drink each time. It actually sends the messages by invoking the 'placeOrder' method on the Cafe
        interface. Above, you will see that the &lt;gateway&gt; element is specified in the configuration file. This
        triggers the creation of a proxy that implements the given 'service-interface' and connects it to a channel.
        The channel name is provided on the @Gateway annotation of the <interfacename>Cafe</interfacename> interface.
        <programlisting language="java">public interface Cafe {

      @Gateway(requestChannel="orders")
      void placeOrder(Order order);

  }</programlisting>
        Finally, have a look at the <methodname>main()</methodname> method of the <classname>CafeDemo</classname> itself.
        <programlisting language="java"><![CDATA[public static void main(String[] args) {
      AbstractApplicationContext context = null;
      if (args.length > 0) {
          context = new FileSystemXmlApplicationContext(args);
      }
      else {
          context = new ClassPathXmlApplicationContext("cafeDemo.xml", CafeDemo.class);
      }
      Cafe cafe = context.getBean("cafe", Cafe.class);
      for (int i = 1; i <= 100; i++) {
          Order order = new Order(i);
          order.addItem(DrinkType.LATTE, 2, false);
          order.addItem(DrinkType.MOCHA, 3, true);
          cafe.placeOrder(order);
      }
  }]]></programlisting>
      </para>
      <tip>
        To run this sample as well as 8 others, refer to the <code>README.txt</code> within the "samples" directory
        of the main distribution as described at the beginning of this chapter.
      </tip>
      <para>
        When you run cafeDemo, you will see that the cold drinks are initially prepared more quickly than the hot drinks.
        Because there is an aggregator, the cold drinks are effectively limited by the rate of the hot drink preparation.
        This is to be expected based on their respective delays of 1000 and 5000 milliseconds. However, by configuring a
        poller with a concurrent task executor, you can dramatically change the results. For example, you could use a
        thread pool executor with 5 workers for the hot drink barista while keeping the cold drink barista as it is:
        <programlisting language="xml"><![CDATA[<service-activator input-channel="hotDrinks"
                     ref="barista"
                     method="prepareHotDrink"
                     output-channel="preparedDrinks"/>

  <service-activator input-channel="hotDrinks"
                     ref="barista"
                     method="prepareHotDrink"
                     output-channel="preparedDrinks">
      ]]><emphasis><![CDATA[<poller task-executor="pool" fixed-rate="1000"/>
          ]]></emphasis><![CDATA[
  </service-activator>

  ]]><emphasis><![CDATA[<task:executor id="pool" pool-size="5"/>]]></emphasis></programlisting>
      </para>
      <para>
        Also, notice that the worker thread name is displayed with each invocation. You will see that the hot drinks are
        prepared by the task-executor threads. If you provide a much shorter poller interval (such as 100 milliseconds),
        then you will notice that occasionally it throttles the input by forcing the task-scheduler (the caller) to invoke
        the operation.
      </para>
      <note>
        In addition to experimenting with the poller's concurrency settings, you can also add the 'transactional'
        sub-element and then refer to any PlatformTransactionManager instance within the context.
      </note>
    </section>

    <section id="samples-xml-messaging">
      <title>The XML Messaging Sample</title>
      <para>
        The xml messaging sample in the <package>org.springframework.integration.samples.xml</package> illustrates how to use
        some of the provided components which deal with xml payloads.  The sample uses the idea of processing an order for books
        represented as xml.
      </para>
      <para>
      First the order is split into a number of messages, each one representing a single order item using
        the XPath splitter component.
          <programlisting language="xml"><![CDATA[<si-xml:xpath-splitter id="orderItemSplitter" input-channel="ordersChannel"
              output-channel="stockCheckerChannel" create-documents="true">
      <si-xml:xpath-expression expression="/orderNs:order/orderNs:orderItem" namespace-map="orderNamespaceMap" />
  </si-xml:xpath-splitter>
  ]]></programlisting>
      </para>
      <para>
        A service activator is then used to pass the message into a stock checker POJO.  The order item document is enriched with information
        from the stock checker about order item stock level.  This enriched order item message is then used to route the message.  In the
        case where the order item is in stock the message is routed to the warehouse.  The XPath router makes use of the default
        <classname>ChannelResolver</classname> strategy which maps the XPath evaluation result to a channel reference in the <classname>ApplicationContext</classname>.
        <programlisting language="xml"><![CDATA[<si-xml:xpath-router id="instockRouter" channel-resolver="mapChannelResolver"
          input-channel="orderRoutingChannel" resolution-required="true">
      <si-xml:xpath-expression expression="/orderNs:orderItem/@in-stock" namespace-map="orderNamespaceMap"  />
  </si-xml:xpath-router>

  ]]></programlisting>
      </para>
      <para>
        Where the order item is not in stock the message is transformed using
        xslt into a format suitable for sending to the supplier.
          <programlisting language="xml"><![CDATA[<si-xml:xslt-transformer input-channel="outOfStockChannel" output-channel="resupplyOrderChannel"
       xsl-resource="classpath:org/springframework/integration/samples/xml/bigBooksSupplierTransformer.xsl"/>
  ]]></programlisting>
      </para>
    </section>
  </section>

</appendix>
