<?xml version="1.0" encoding="UTF-8"?>
<chapter xml:id="actions"
	xmlns="http://docbook.org/ns/docbook" version="5.0"
	xmlns:xl="http://www.w3.org/1999/xlink"
	xmlns:xi="http://www.w3.org/2001/XInclude"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="
		http://docbook.org/ns/docbook http://www.docbook.org/xml/5.0/xsd/docbook.xsd
		http://www.w3.org/1999/xlink http://www.docbook.org/xml/5.0/xsd/xlink.xsd">
	<title>Executing actions</title>
	<sect1 xml:id="actions-introduction">
		<title>Introduction</title>
		<para>
			This chapter shows you how to use the <code>action-state</code> element to control the execution of an action at a point within a flow.
			It will also show how to use the <code>decision-state</code> element to make a flow routing decision.
			Finally, several examples of invoking actions from the various points possible within a flow will be discussed.
		</para>
	</sect1>
	<sect1 xml:id="action-state">
		<title>Defining action states</title>
		<para>
			Use the <code>action-state</code> element when you wish to invoke an action, then transition to another state based on the action's outcome:
		</para>
		<programlisting language="xml"><![CDATA[
<action-state id="moreAnswersNeeded">
	<evaluate expression="interview.moreAnswersNeeded()" />
	<transition on="yes" to="answerQuestions" />
	<transition on="no" to="finish" />
</action-state>]]>
		</programlisting>
		<para>
			The full example below illustrates a interview flow that uses the action-state above to determine if more answers are needed to complete the interview:
		</para>
		<programlisting language="xml"><![CDATA[
<flow xmlns="http://www.springframework.org/schema/webflow"
	  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	  xsi:schemaLocation="http://www.springframework.org/schema/webflow
						  http://www.springframework.org/schema/webflow/spring-webflow.xsd">

	<on-start>
		<evaluate expression="interviewFactory.createInterview()" result="flowScope.interview" />
	</on-start>

	<view-state id="answerQuestions" model="questionSet">
		<on-entry>
			<evaluate expression="interview.getNextQuestionSet()" result="viewScope.questionSet" />
		</on-entry>
		<transition on="submitAnswers" to="moreAnswersNeeded">
			<evaluate expression="interview.recordAnswers(questionSet)" />
		</transition>
	</view-state>

	<action-state id="moreAnswersNeeded">
		<evaluate expression="interview.moreAnswersNeeded()" />
		<transition on="yes" to="answerQuestions" />
		<transition on="no" to="finish" />
	</action-state>

	<end-state id="finish" />

</flow>]]>
			</programlisting>
		<para>
			After the execution of each action, the action-state checks the result to see if matches a declared
			transition to another state. That means if more than one action is configured they are executed in
			an ordered chain until one returns a result event that matches a state transition out of the
			action-state while the rest are ignored. This is a form of the Chain of Responsibility (CoR) pattern.
		</para>
		<para>
			The result of an action's execution is typically the criteria for a transition out of this state.
			Additional information in the current RequestContext may also be tested as part of custom
			transitional criteria allowing for sophisticated transition expressions that reason on contextual
			state.
		</para>
		<para>
			Note also that an action-state just like any other state can have one more on-entry actions
			that are executed as a list from start to end.
		</para>
	</sect1>
	<sect1 xml:id="decision-state">
		<title>Defining decision states</title>
		<para>
			Use the <code>decision-state</code> element as an alternative to the action-state to make a routing decision using a convenient if/else syntax.
			The example below shows the <code>moreAnswersNeeded</code> state above now implemented as a decision state instead of an action-state:
		</para>
		<programlisting language="xml"><![CDATA[
<decision-state id="moreAnswersNeeded">
	<if test="interview.moreAnswersNeeded()" then="answerQuestions" else="finish" />
</decision-state>]]>
			</programlisting>
	</sect1>
	<sect1 xml:id="action-outcome-events">
		<title>Action outcome event mappings</title>
		<para>
			Actions often invoke methods on plain Java objects.
			When called from action-states and decision-states, these method return values can be used to drive state transitions.
			Since transitions are triggered by events, a method return value must first be mapped to an Event object.
			The following table describes how common return value types are mapped to Event objects:
		</para>
		<table xml:id="event-mapping-table">
			<title>Action method return value to event id mappings</title>
			<tgroup cols="2">
				<colspec colname="Method return type" colwidth="*"/>
				<colspec colname="Event identifier" colwidth="3*"/>
				<thead>
					<row>
						<entry>Method return type</entry>
						<entry>Mapped Event identifier expression</entry>
					</row>
				</thead>
				<tbody>
					<row>
						<entry>java.lang.String</entry>
						<entry>the String value</entry>
					</row>
					<row>
						<entry>java.lang.Boolean</entry>
						<entry>yes (for true), no (for false)</entry>
					</row>
					<row>
						<entry>java.lang.Enum</entry>
						<entry>the Enum name</entry>
					</row>
					<row>
						<entry>any other type</entry>
						<entry>success</entry>
					</row>
				</tbody>
			</tgroup>
		</table>
		<para>
			This is illustrated in the example action state below, which invokes a method that returns a boolean value:
		</para>
		<programlisting language="xml"><![CDATA[
<action-state id="moreAnswersNeeded">
	<evaluate expression="interview.moreAnswersNeeded()" />
	<transition on="yes" to="answerQuestions" />
	<transition on="no" to="finish" />
</action-state>]]>
		</programlisting>
	</sect1>
	<sect1 xml:id="action-implementations">
		<title>Action implementations</title>
		<para>
			While writing action code as POJO logic is the most common, there are several other action implementation options.
			Sometimes you need to write action code that needs access to the flow context.
			You can always invoke a POJO and pass it the flowRequestContext as an EL variable.
			Alternatively, you may implement the <code>Action</code> interface or extend from the <code>MultiAction</code> base class.
			These options provide stronger type safety when you have a natural coupling between your action code and Spring Web Flow APIs.
			Examples of each of these approaches are shown below.
		</para>
		<sect2>
			<title>Invoking a POJO action</title>
			<programlisting language="xml"><![CDATA[
<evaluate expression="pojoAction.method(flowRequestContext)" />]]>
			</programlisting>
			<programlisting language="java"><![CDATA[
public class PojoAction {
	public String method(RequestContext context) {
		...
	}
}]]>
			</programlisting>
		</sect2>
		<sect2>
			<title>Invoking a custom Action implementation</title>
			<programlisting language="xml"><![CDATA[
<evaluate expression="customAction" />]]>
			</programlisting>
			<programlisting language="java"><![CDATA[
public class CustomAction implements Action {
	public Event execute(RequestContext context) {
		...
	}
}]]>
			</programlisting>
		</sect2>
		<sect2>
			<title>Invoking a MultiAction implementation</title>
			<programlisting language="xml"><![CDATA[
<evaluate expression="multiAction.actionMethod1" />
]]>
			</programlisting>
			<programlisting language="java"><![CDATA[
public class CustomMultiAction extends MultiAction {
	public Event actionMethod1(RequestContext context) {
		...
	}

	public Event actionMethod2(RequestContext context) {
		...
	}

	...
}]]>
			</programlisting>
		</sect2>
	</sect1>
	<sect1 xml:id="action-exceptions">
		<title>Action exceptions</title>
		<para>
			Actions often invoke services that encapsulate complex business logic.
			These services may throw business exceptions that the action code should handle.
		</para>
		<sect2>
			<title>Handling a business exception with a POJO action</title>
			<para>
				The following example invokes an action that catches a business exception, adds a error message to the context, and returns a result event identifier.
				The result is treated as a flow event which the calling flow can then respond to.
			</para>
			<programlisting language="xml"><![CDATA[
<evaluate expression="bookingAction.makeBooking(booking, flowRequestContext)" />]]>
			</programlisting>
			<programlisting language="java"><![CDATA[
public class BookingAction {
public String makeBooking(Booking booking, RequestContext context) {
	   try {
		   BookingConfirmation confirmation = bookingService.make(booking);
		   context.getFlowScope().put("confirmation", confirmation);
		   return "success";
	   } catch (RoomNotAvailableException e) {
		   context.addMessage(new MessageBuilder().error().
			   .defaultText("No room is available at this hotel").build());
		   return "error";
	   }
}
}]]>
			</programlisting>
		</sect2>
		<sect2>
			<title>Handling a business exception with a MultiAction</title>
			<para>
				The following example is functionally equivlant to the last, but implemented as a MultiAction instead of a POJO action.
				The MultiAction requires its action methods to be of the signature <code>Event ${methodName}(RequestContext)</code>, providing stronger type safety, while a POJO action allows for more freedom.
			</para>
			<programlisting language="xml"><![CDATA[
<evaluate expression="bookingAction.makeBooking" />]]>
			</programlisting>
			<programlisting language="java"><![CDATA[
public class BookingAction extends MultiAction {
public Event makeBooking(RequestContext context) {
	   try {
		   Booking booking = (Booking) context.getFlowScope().get("booking");
		   BookingConfirmation confirmation = bookingService.make(booking);
		   context.getFlowScope().put("confirmation", confirmation);
		   return success();
	   } catch (RoomNotAvailableException e) {
		   context.getMessageContext().addMessage(new MessageBuilder().error().
			   .defaultText("No room is available at this hotel").build());
		   return error();
	   }
}
}]]>
			</programlisting>
		</sect2>
		<sect2>
			<title>Using an exception-handler element</title>
			<para>
				In general it is recommended to catch exceptions in actions and return result
				events that drive standard transitions, it is also possible to add an
				<code>exception-handler</code> sub-element to any state type with a
				<code>bean</code> attribute referencing a bean of type
				<classname>FlowExecutionExceptionHandler</classname>. This is an advanced
				option that if used incorrectly can leave the flow execution in an invalid state.
				Consider the build-in <classname>TransitionExecutingFlowExecutionExceptionHandler</classname>
				as example of a correct implementation. 
			</para>
		</sect2>
	</sect1>
	<sect1 xml:id="action-examples">
		<title>Other Action execution examples</title>
		<sect2 xml:id="action-on-start">
			<title>on-start</title>
			<para>
				The following example shows an action that creates a new Booking object by invoking a method on a service:
			</para>
			<programlisting language="xml"><![CDATA[
<flow xmlns="http://www.springframework.org/schema/webflow"
	  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	  xsi:schemaLocation="http://www.springframework.org/schema/webflow
						  http://www.springframework.org/schema/webflow/spring-webflow.xsd">

	<input name="hotelId" />

	<on-start>
		<evaluate expression="bookingService.createBooking(hotelId, currentUser.name)"
				  result="flowScope.booking" />
	</on-start>

</flow>]]>
			</programlisting>
		</sect2>
		<sect2 xml:id="action-on-state-entry">
			<title>on-entry</title>
			<para>
				The following example shows a state entry action that sets the special <code>fragments</code> variable that causes the view-state to render a partial fragment of its view:
			</para>
			<programlisting language="xml"><![CDATA[
<view-state id="changeSearchCriteria" view="enterSearchCriteria.xhtml" popup="true">
	<on-entry>
		<render fragments="hotelSearchForm" />
	</on-entry>
</view-state>]]>
			</programlisting>
		</sect2>
		<sect2 xml:id="action-on-state-exit">
			<title>on-exit</title>
			<para>
				The following example shows a state exit action that releases a lock on a record being edited:
			</para>
			<programlisting language="xml"><![CDATA[
<view-state id="editOrder">
	<on-entry>
		<evaluate expression="orderService.selectForUpdate(orderId, currentUser)"
				  result="viewScope.order" />
	</on-entry>
	<transition on="save" to="finish">
		<evaluate expression="orderService.update(order, currentUser)" />
	</transition>
	<on-exit>
		<evaluate expression="orderService.releaseLock(order, currentUser)" />
	</on-exit>
</view-state>]]>
			</programlisting>
		</sect2>
		<sect2 xml:id="on-end">
			<title>on-end</title>
			<para>
				The following example shows the equivalent object locking behavior using flow start and end actions:
			</para>
			<programlisting language="xml"><![CDATA[
<flow xmlns="http://www.springframework.org/schema/webflow"
	  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	  xsi:schemaLocation="http://www.springframework.org/schema/webflow
						  http://www.springframework.org/schema/webflow/spring-webflow.xsd">

	<input name="orderId" />

	<on-start>
		<evaluate expression="orderService.selectForUpdate(orderId, currentUser)"
				  result="flowScope.order" />
	</on-start>

	<view-state id="editOrder">
		<transition on="save" to="finish">
			<evaluate expression="orderService.update(order, currentUser)" />
		</transition>
	</view-state>

	<on-end>
		<evaluate expression="orderService.releaseLock(order, currentUser)" />
	</on-end>

</flow>]]>
			</programlisting>
		</sect2>
		<sect2 xml:id="action-on-render">
			<title>on-render</title>
			<para>
				The following example shows a render action that loads a list of hotels to display before the view is rendered:
			</para>
			<programlisting language="xml"><![CDATA[
<view-state id="reviewHotels">
	<on-render>
		<evaluate expression="bookingService.findHotels(searchCriteria)"
				  result="viewScope.hotels" result-type="dataModel" />
	</on-render>
	<transition on="select" to="reviewHotel">
		<set name="flowScope.hotel" value="hotels.selectedRow" />
	</transition>
</view-state>]]>
			</programlisting>
		</sect2>
		<sect2 xml:id="action-on-transition">
			<title>on-transition</title>
			<para>
				The following example shows a transition action adds a subflow outcome event attribute to a collection:
			</para>
			<programlisting language="xml"><![CDATA[
<subflow-state id="addGuest" subflow="createGuest">
	<transition on="guestCreated" to="reviewBooking">
		<evaluate expression="booking.guestList.add(currentEvent.attributes.newGuest)" />
	</transition>
</subfow-state>]]>
			</programlisting>
		</sect2>
		<sect2 xml:id="named-actions">
			<title>Named actions</title>
			<para>
				The following example shows how to execute a chain of actions in an action-state.
				The name of each action becomes a qualifier for the action's result event.
			</para>
			<programlisting language="xml"><![CDATA[
<action-state id="doTwoThings">
	<evaluate expression="service.thingOne()">
		<attribute name="name" value="thingOne" />
	</evaluate>
	<evaluate expression="service.thingTwo()">
		<attribute name="name" value="thingTwo" />
	</evaluate>
	<transition on="thingTwo.success" to="showResults" />
</action-state>]]>
			</programlisting>
			<para>
				In this example, the flow will transition to <code>showResults</code> when <code>thingTwo</code>
				completes successfully.
			</para>
		</sect2>
		<sect2 xml:id="streaming-actions">
			<title>Streaming actions</title>
			<para>
				Sometimes an Action needs to stream a custom response back to the client.
				An example might be a flow that renders a PDF document when handling a print event.
				This can be achieved by having the action stream the content then record "Response Complete" status on the ExternalContext.
				The responseComplete flag tells the pausing view-state not to render the response because another object has taken care of it.
			</para>
			<programlisting language="xml"><![CDATA[
<view-state id="reviewItinerary">
	<transition on="print">
		<evaluate expression="printBoardingPassAction" />
	</transition>
</view-state>]]>
			</programlisting>
			<programlisting language="java"><![CDATA[
public class PrintBoardingPassAction extends AbstractAction {
	public Event doExecute(RequestContext context) {
		// stream PDF content here...
		// - Access HttpServletResponse by calling context.getExternalContext().getNativeResponse();
		// - Mark response complete by calling context.getExternalContext().recordResponseComplete();
		return success();
	}
}]]>
			</programlisting>
			<para>
				In this example, when the print event is raised the flow will call the printBoardingPassAction.
				The action will render the PDF then mark the response as complete.
			</para>
		</sect2>
		<sect2 xml:id="file-upload">
			<title>Handling File Uploads</title>
			<para>
				Another common task is to use Web Flow to handle multipart file uploads in combination with Spring MVC's
				<code>MultipartResolver</code>.  Once the resolver is set up correctly <link xl:href="http://static.springsource.org/spring/docs/2.5.x/reference/mvc.html#mvc-multipart">as described here</link> and the submitting
				HTML form is configured with <code>enctype="multipart/form-data"</code>, you can easily handle the file upload in a
				transition action.
			</para>
			<note>
				<para>
					The file upload example below below is not relevant when using Web Flow with JSF. See
					<xref linkend="spring-faces-file-upload"/> for details of how to upload files using JSF.
				</para>
			</note>
			<para>
				Given a form such as:
			</para>
			<programlisting language="xml"><![CDATA[
<form:form modelAttribute="fileUploadHandler" enctype="multipart/form-data">
	Select file: <input type="file" name="file"/>
	<input type="submit" name="_eventId_upload" value="Upload" />
</form:form>]]>
			</programlisting>
			<para>
				and a backing object for handling the upload such as:
			</para>
			<programlisting language="java"><![CDATA[
package org.springframework.webflow.samples.booking;

import org.springframework.web.multipart.MultipartFile;

public class FileUploadHandler {

	private transient MultipartFile file;

	public void processFile() {
		//Do something with the MultipartFile here
	}

	public void setFile(MultipartFile file) {
		this.file = file;
	}
}]]>
			</programlisting>
			<para>
				you can process the upload using a transition action as in the following example:
			</para>
			<programlisting language="xml"><![CDATA[
<view-state id="uploadFile" model="uploadFileHandler">
	<var name="fileUploadHandler" class="org.springframework.webflow.samples.booking.FileUploadHandler" />
	<transition on="upload" to="finish" >
		<evaluate expression="fileUploadHandler.processFile()"/>
	</transition>
	<transition on="cancel" to="finish" bind="false"/>
</view-state>]]>
			</programlisting>
			<para>
				The <code>MultipartFile</code> will be bound to the <code>FileUploadHandler</code> bean as
				part of the normal form binding process so that it will be available to process during the
				execution of the transition action.
			</para>
		</sect2>
	</sect1>
</chapter>
