Spring Web Flow Reference Guide

For milestones and snapshots you'll need to use the SpringSource repository. Add the following repository to your Maven pom.xml:

<repository>
    <id>springsource-repository</id>
    <name>Spring project snapshots, milestones, and releases</name>
    <url>http://repo.springsource.org/snapshot</url>
</repository>
			

Then declare the following dependencies:

<dependency>
    <groupId>org.springframework.webflow</groupId>
    <artifactId>spring-binding</artifactId>
    <version>x.y.z.BUILD-SNAPSHOT</version>
</dependency> 

<dependency>
    <groupId>org.springframework.webflow</groupId>
    <artifactId>spring-js</artifactId>
    <version>x.y.z.BUILD-SNAPSHOT</version>
</dependency> 

<dependency>
    <groupId>org.springframework.webflow</groupId>
    <artifactId>spring-webflow</artifactId>
    <version>x.y.z.BUILD-SNAPSHOT</version>
</dependency>
			

And if using JavaServerFaces:

<dependency>
    <groupId>org.springframework.webflow</groupId>
    <artifactId>spring-faces</artifactId>
    <version>x.y.z.BUILD-SNAPSHOT</version>
</dependency>
			

By default Web Flow does a client-side redirect upon entering every view state. That makes it impossible to embed a flow on a page or within a modal dialog and execute more than one view state without causing a full-page refresh. Web Flow now supports launching a flow in "embedded" mode. In this mode a flow can transition to other view states without a client-side redirect during Ajax requests. See Section 11.7, “Embedding A Flow On A Page” and Section 13.9, “Embedding a Flow On a Page”.

Support for the JSR-303 Bean Validation API is now available building on equivalent support available in Spring MVC. See Section 5.10, “Validating a model” for more details.

Starting with Web Flow 2.3 a flow managed PersistenceContext is automatically extended (propagated) to sub-flows assuming the subflow also has the feature enabled as well. See Section 7.3, “Flow Managed Persistence And Sub-Flows”.

Support for Portlet 2.0 resource requests has now been added enabling Ajax requests with partial rendering. URLs for such requests can be prepared with the <portlet:resourceURL> tag in JSP pages. Server-side processing is similar to a combined an action and a render requests but combined in a single request. Unlike a render request, the response from a resource request includes content from the target portlet only.

The <flow-execution-repository> element now provides a conversation-manager attribute accepting a reference to a ConversationManager instance.

By default Web Flow does a client-side redirect when remaining in the same view state as long as the current request is not an Ajax request. This is useful after form validation failure. Hitting Refresh or Back won't result in browser warnings. Hence this behavior is usually desirable. However a new flow execution attribute makes it possible to disable it and that may also be necessary in some cases specific to JSF 2 applications. See Section 13.10, “Redirect In Same State”.

The process for building the samples included with the distribution has been simplified. Maven can be used to build all samples in one step. Eclipse settings include source code references to simplify debugging.

Additional samples can be accessed as follows:

mkdir spring-samples
cd spring-samples
svn co https://src.springframework.org/svn/spring-samples/webflow-primefaces-showcase
cd webflow-primefaces-showcase
mvn package
# import into Eclipse

mkdir spring-samples
cd spring-samples
svn co https://src.springframework.org/svn/spring-samples/webflow-showcase
cd webflow-showcase
mvn package
# import into Eclipse

A new Spring Security tag library is available for use with with JSF 2.0 or with JSF 1.2 Facelets views. It provides an <authorize> tag as well as several EL functions. See Section 13.11, “Using the Spring Security Facelets Tag Library” for more details.

Every flow begins with the following root element:

<?xml version="1.0" encoding="UTF-8"?>
<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-2.0.xsd">

</flow>
			

All states of the flow are defined within this element. The first state defined becomes the flow's starting point.

Use the view-state element to define a step of the flow that renders a view:

<view-state id="enterBookingDetails" />
			

By convention, a view-state maps its id to a view template in the directory where the flow is located. For example, the state above might render /WEB-INF/hotels/booking/enterBookingDetails.xhtml if the flow itself was located in the /WEB-INF/hotels/booking directory.

Use the transition element to handle events that occur within a state:

<view-state id="enterBookingDetails">
    <transition on="submit" to="reviewBooking" />
</view-state>
			

These transitions drive view navigations.

Use the end-state element to define a flow outcome:

<end-state id="bookingCancelled" />
			

When a flow transitions to a end-state it terminates and the outcome is returned.

With the three elements view-state, transition, and end-state, you can quickly express your view navigation logic. Teams often do this before adding flow behaviors so they can focus on developing the user interface of the application with end users first. Below is a sample flow that implements its view navigation logic using these elements:

<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-2.0.xsd">

    <view-state id="enterBookingDetails">
        <transition on="submit" to="reviewBooking" />
    </view-state>
	
    <view-state id="reviewBooking">
        <transition on="confirm" to="bookingConfirmed" />
        <transition on="revise" to="enterBookingDetails" />
        <transition on="cancel" to="bookingCancelled" />
    </view-state>
	
    <end-state id="bookingConfirmed" />

    <end-state id="bookingCancelled" />
		
</flow>	
			

The action element you will use most often is the evaluate element. Use the evaluate element to evaluate an expression at a point within your flow. With this single tag you can invoke methods on Spring beans or any other flow variable. For example:

<evaluate expression="entityManager.persist(booking)" />		
			

<evaluate expression="bookingService.findHotels(searchCriteria)" result="flowScope.hotels" />
				

<evaluate expression="bookingService.findHotels(searchCriteria)" result="flowScope.hotels"
          result-type="dataModel"/>
				

Now review the sample booking flow with actions added:

<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-2.0.xsd">

    <input name="hotelId" />

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

    <view-state id="enterBookingDetails">
        <transition on="submit" to="reviewBooking" />
    </view-state>
	
    <view-state id="reviewBooking">
        <transition on="confirm" to="bookingConfirmed" />
        <transition on="revise" to="enterBookingDetails" />
        <transition on="cancel" to="bookingCancelled" />
    </view-state>
	
    <end-state id="bookingConfirmed" />

    <end-state id="bookingCancelled" />
		
</flow>	
			

This flow now creates a Booking object in flow scope when it starts. The id of the hotel to book is obtained from a flow input attribute.

Use the input element to declare a flow input attribute:

<input name="hotelId" />
			

Input values are saved in flow scope under the name of the attribute. For example, the input above would be saved under the name hotelId.

<input name="hotelId" type="long" />
				

<input name="hotelId" value="flowScope.myParameterObject.hotelId" />
				

<input name="hotelId" type="long" value="flowScope.hotelId" required="true" />
				

Use the output element to declare a flow output attribute. Output attributes are declared within end-states that represent specific flow outcomes.

<end-state id="bookingConfirmed">
    <output name="bookingId" />  
</end-state>
			

Output values are obtained from flow scope under the name of the attribute. For example, the output above would be assigned the value of the bookingId variable.

<output name="confirmationNumber" value="booking.confirmationNumber" />  
				

Now review the sample booking flow with input/output mapping:

<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-2.0.xsd">

    <input name="hotelId" />

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

    <view-state id="enterBookingDetails">
        <transition on="submit" to="reviewBooking" />
    </view-state>
	
    <view-state id="reviewBooking">
        <transition on="confirm" to="bookingConfirmed" />
        <transition on="revise" to="enterBookingDetails" />
        <transition on="cancel" to="bookingCancelled" />
    </view-state>
	
    <end-state id="bookingConfirmed" >
        <output name="bookingId" value="booking.id"/>
    </end-state>

    <end-state id="bookingCancelled" />
		
</flow>	
			

The flow now accepts a hotelId input attribute and returns a bookingId output attribute when a new booking is confirmed.

Use the var element to declare a flow variable:

<var name="searchCriteria" class="com.mycompany.myapp.hotels.search.SearchCriteria"/>
			

Make sure your variable's class implements java.io.Serializable, as the instance state is saved between flow requests.

Use the subflow-state element to call another flow as a subflow:

<subflow-state id="addGuest" subflow="createGuest">
    <transition on="guestCreated" to="reviewBooking">
        <evaluate expression="booking.guests.add(currentEvent.attributes.guest)" />  
    </transition>
    <transition on="creationCancelled" to="reviewBooking" />
</subflow-state>
			

The above example calls the createGuest flow, then waits for it to return. When the flow returns with a guestCreated outcome, the new guest is added to the booking's guest list.

<subflow-state id="addGuest" subflow="createGuest">
    <input name="booking" />
    <transition to="reviewBooking" />
</subflow-state>
				

<transition on="guestCreated" to="reviewBooking">
    <evaluate expression="booking.guests.add(currentEvent.attributes.guest)" />  
</transition>
				

Now review the sample booking flow calling a subflow:

<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-2.0.xsd">

    <input name="hotelId" />

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

    <view-state id="enterBookingDetails">
        <transition on="submit" to="reviewBooking" />
    </view-state>

    <view-state id="reviewBooking">
        <transition on="addGuest" to="addGuest" />
        <transition on="confirm" to="bookingConfirmed" />
        <transition on="revise" to="enterBookingDetails" />
        <transition on="cancel" to="bookingCancelled" />
    </view-state>

    <subflow-state id="addGuest" subflow="createGuest">
        <transition on="guestCreated" to="reviewBooking">
            <evaluate expression="booking.guests.add(currentEvent.attributes.guest)" />  
        </transition>
        <transition on="creationCancelled" to="reviewBooking" />
    </subflow-state>
		
    <end-state id="bookingConfirmed" >
        <output name="bookingId" value="booking.id" />
    </end-state>

    <end-state id="bookingCancelled" />
		
</flow>		
			

The flow now calls a createGuest subflow to add a new guest to the guest list.

An important concept to understand is there are two types of expressions in Web Flow: standard expressions and template expressions.

<evaluate expression="searchCriteria.nextPage()" />
				

Template expressions

The second type of expression is a template expression. A template expression allows mixing of literal text with one or more standard expressions. Each standard expression block is explicitly surrounded with the #{} delimiters. For example:

<view-state id="error" view="error-#{externalContext.locale}.xhtml" />
				

The expression above is a template expression. The result of evaluation will be a string that concatenates literal text such as error- and .xhtml with the result of evaluating externalContext.locale. As you can see, explicit delimiters are necessary here to demarcate standard expression blocks within the template.

	Note
	See the Web Flow XML schema for a complete listing of those XML attributes that accept standard expressions and those that accept template expressions. You can also use F2 in Eclipse (or equivalent shortcut in other IDEs) to access available documentation when typing out specific flow definition attributes.

Starting with version 2.1 Web Flow uses the Spring Expression Language (Spring EL). Spring EL was created to provide is a single, well-supported expression language for use across all the products in the Spring portfolio. It is distributed as a separate jar org.springframework.expression in the Spring Framework. Existing applications will need to remove dependencies on org.jboss.el or org.ognl and use org.springframework.expression instead. See the section below on EL Portability for other notes on upgrading.

In Web Flow 2.0 Unified EL was the default expression language with jboss-el as the implementation. Use of Unified EL also implies a dependency on el-api although that is typically provided by your web container. Tomcat 6 includes it, for example. Spring EL is the default and recommended expression language to use. However it is possible to replace it with Unified EL if you wish to do so. You need the following Spring configuration to plug in the WebFlowELExpressionParser to the flow-builder-services:

<webflow:flow-builder-services expression-parser="expressionParser"/>

<bean id="expressionParser" class="org.springframework.webflow.expression.el.WebFlowELExpressionParser">
    <constructor-arg>
        <bean class="org.jboss.el.ExpressionFactoryImpl" />
    </constructor-arg>
</bean>
                

Note that if your application is registering custom converters it's important to ensure the WebFlowELExpressionParser is configured with the conversion service that has those custom converters.

<webflow:flow-builder-services expression-parser="expressionParser" conversion-service="conversionService"/>

<bean id="expressionParser" class="org.springframework.webflow.expression.el.WebFlowELExpressionParser">
    <constructor-arg>
        <bean class="org.jboss.el.ExpressionFactoryImpl" />
    </constructor-arg>
    <property name="conversionService" ref="conversionService"/>
</bean>

<bean id="conversionService" class="somepackage.ApplicationConversionService"/>
                

OGNL is the third supported expression language. OGNL is the EL most familiar to Web Flow version 1.0 users. Please refer to the OGNL language guide for specifics on its EL syntax. If you wish to use OGNL this is the Spring configuration necessary to plug it in:

<webflow:flow-builder-services expression-parser="expressionParser"/>

<bean id="expressionParser" class="org.springframework.webflow.expression.WebFlowOgnlExpressionParser"/>
                

Note that if your application is registering custom converters it's important to ensure the WebFlowOgnlExpressionParser is configured with the conversion service that has those custom converters.

<webflow:flow-builder-services expression-parser="expressionParser" conversion-service="conversionService"/>

<bean id="expressionParser" class="org.springframework.webflow.expression.WebFlowOgnlExpressionParser">
    <property name="conversionService" ref="conversionService"/>
</bean>

<bean id="conversionService" class="somepackage.ApplicationConversionService"/>
                

Use flowScope to assign a flow variable. Flow scope gets allocated when a flow starts and destroyed when the flow ends. With the default implementation, any objects stored in flow scope need to be Serializable.

<evaluate expression="searchService.findHotel(hotelId)" result="flowScope.hotel" />
			

Use viewScope to assign a view variable. View scope gets allocated when a view-state enters and destroyed when the state exits. View scope is only referenceable from within a view-state. With the default implementation, any objects stored in view scope need to be Serializable.

<on-render>
    <evaluate expression="searchService.findHotels(searchCriteria)" result="viewScope.hotels"
              result-type="dataModel" />
</on-render>
			

Use requestScope to assign a request variable. Request scope gets allocated when a flow is called and destroyed when the flow returns.

<set name="requestScope.hotelId" value="requestParameters.id" type="long" />
			

Use flashScope to assign a flash variable. Flash scope gets allocated when a flow starts, cleared after every view render, and destroyed when the flow ends. With the default implementation, any objects stored in flash scope need to be Serializable.

<set name="flashScope.statusMessage" value="'Booking confirmed'" />				
			

Use conversationScope to assign a conversation variable. Conversation scope gets allocated when a top-level flow starts and destroyed when the top-level flow ends. Conversation scope is shared by a top-level flow and all of its subflows. With the default implementation, conversation scoped objects are stored in the HTTP session and should generally be Serializable to account for typical session replication.

<evaluate expression="searchService.findHotel(hotelId)" result="conversationScope.hotel" />
			

Use requestParameters to access a client request parameter:

<set name="requestScope.hotelId" value="requestParameters.id" type="long" />
			

Use currentEvent to access attributes of the current Event:

<evaluate expression="booking.guests.add(currentEvent.attributes.guest)" />
			

Use currentUser to access the authenticated Principal:

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

Use messageContext to access a context for retrieving and creating flow execution messages, including error and success messages. See the MessageContext Javadocs for more information.

<evaluate expression="bookingValidator.validate(booking, messageContext)" />
			

Use resourceBundle to access a message resource.

<set name="flashScope.successMessage" value="resourceBundle.successMessage" />
			

Use flowRequestContext to access the RequestContext API, which is a representation of the current flow request. See the API Javadocs for more information.

Use flowExecutionContext to access the FlowExecutionContext API, which is a representation of the current flow state. See the API Javadocs for more information.

Use flowExecutionUrl to access the context-relative URI for the current flow execution view-state.

Use externalContext to access the client environment, including user session attributes. See the ExternalContext API JavaDocs for more information.

<evaluate expression="searchService.suggestHotels(externalContext.sessionMap.userProfile)" 
          result="viewScope.hotels" />
			

The view id may be a relative path to view resource in the flow's working directory:

<view-state id="enterBookingDetails" view="bookingDetails.xhtml">
			

The view id may be a absolute path to a view resource in the webapp root directory:

<view-state id="enterBookingDetails" view="/WEB-INF/hotels/booking/bookingDetails.xhtml">
			

With some view frameworks, such as Spring MVC's view framework, the view id may also be a logical identifier resolved by the framework:

<view-state id="enterBookingDetails" view="bookingDetails">
			

See the Spring MVC integration section for more information on how to integrate with the MVC ViewResolver infrastructure.

Use the var tag to declare a view variable. Like a flow variable, any @Autowired references are automatically restored when the view state resumes.

<var name="searchCriteria" class="com.mycompany.myapp.hotels.SearchCriteria" />
			

Use the on-render tag to assign a variable from an action result before the view renders:

<on-render>
    <evaluate expression="bookingService.findHotels(searchCriteria)" result="viewScope.hotels" />
</on-render>
			

Objects in view scope are often manipulated over a series of requests from the same view. The following example pages through a search results list. The list is updated in view scope before each render. Asynchronous event handlers modify the current data page, then request re-rendering of the search results fragment.

<view-state id="searchResults">
    <on-render>
        <evaluate expression="bookingService.findHotels(searchCriteria)"
                  result="viewScope.hotels" />
    </on-render>
    <transition on="next">
        <evaluate expression="searchCriteria.nextPage()" />
        <render fragments="searchResultsFragment" />            
    </transition>
    <transition on="previous">
        <evaluate expression="searchCriteria.previousPage()" />
        <render fragments="searchResultsFragment" />          
    </transition>
</view-state>
			

Starting with version 2.1 Spring Web Flow uses the type conversion and formatting system introduced in Spring 3 for nearly all type conversion needs. Previously Web Flow applications used a type conversion mechanism that was different from the one in Spring MVC, which relied on the java.beans.PropertyEditor abstraction. Spring 3 offers a modern type conversion alternative to PropertyEditors that was actually influenced by Web Flow's own type conversion system. Hence Web Flow users should find it natural to work with the new Spring 3 type conversion. Another obvious and very important benefit of this change is that a single type conversion mechanism can now be used across Spring MVC And Spring Web Flow.

What does this practically mean for existing applications? Existing applications are likely registering their own converters of type org.springframework.binding.convert.converters.Converter through a sub-class of DefaultConversionService available in Spring Binding. Those converters can continue to be registered as before. They will be adapted as Spring 3 GenericConverter types and registered with a Spring 3 org.springframework.core.convert.ConversionService instance. In other words existing converters will be invoked through Spring's type conversion service.

The only exception to this rule are named converters, which can be referenced from a binding element in a view-state:

public class ApplicationConversionService extends DefaultConversionService {	
    public ApplicationConversionService() {
        addDefaultConverters();
        addDefaultAliases();
        addConverter("customConverter", new CustomConverter());		
    }
}
				

<view-state id="enterBookingDetails" model="booking">
    <binder>
        <binding property="checkinDate" required="true" converter="customConverter" />
    </binder>
</view-state>
				

Named converters are not supported and cannot be used with the type conversion service available in Spring 3. Therefore such converters will not be adapted and will continue to work as before, i.e. will not involve the Spring 3 type conversion. However, this mechanism is deprecated and applications are encouraged to favor Spring 3 type conversion and formatting features.

Also note that the existing Spring Binding DefaultConversionService no longer registers any default converters. Instead Web Flow now relies on the default type converters and formatters in Spring 3.

In summary the Spring 3 type conversion and formatting is now used almost exclusively in Web Flow. Although existing applications will work without any changes, we encourage moving towards unifying the type conversion needs of Spring MVC and Spring Web Flow parts of applications.

In Spring MVC an instance of a FormattingConversionService is created automatically through the custom MVC namespace:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xsi:schemaLocation="
        http://www.springframework.org/schema/mvc 
        http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd
        http://www.springframework.org/schema/beans 
        http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

	<mvc:annotation-driven/>

				

Internally that is done with the help of FormattingConversionServiceFactoryBean, which registers a default set of converters and formatters. You can customize the conversion service instance used in Spring MVC through the conversion-service attribute:

<mvc:annotation-driven conversion-service="applicationConversionService" />
				

In Web Flow an instance of a Spring Binding DefaultConversionService is created automatically, which does not register any converters. Instead it delegates to a FormattingConversionService instance for all type conversion needs. By default this is not the same FormattingConversionService instance as the one used in Spring 3. However that won't make a practical difference until you start registering your own formatters.

The DefaultConversionService used in Web Flow can be customized through the flow-builder-services element:

<webflow:flow-builder-services id="flowBuilderServices" conversion-service="defaultConversionService" />
				

Connecting the dots in order to register your own formatters for use in both Spring MVC and in Spring Web Flow you can do the following. Create a class to register your custom formatters:

public class ApplicationConversionServiceFactoryBean extends FormattingConversionServiceFactoryBean {

    @Override
    protected void installFormatters(FormatterRegistry registry) {
        // ...
    }
	
}				

				

Configure it for use in Spring MVC:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xsi:schemaLocation="
        http://www.springframework.org/schema/mvc 
        http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd
        http://www.springframework.org/schema/beans 
        http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

    <mvc:annotation-driven conversion-service="applicationConversionService" />
	
    <!-- 
    	Alternatively if you prefer annotations for DI:
    	  1. Add @Component to the factory bean.
    	  2. Add a component-scan element (from the context custom namespace) here.
    	  3. Remove XML bean declaration below.
      -->

    <bean id="applicationConversionService" class="somepackage.ApplicationConversionServiceFactoryBean">
	

				

Connection the Web Flow DefaultConversionService to the same "applicationConversionService" bean used in Spring MVC:

    <webflow:flow-registry id="flowRegistry" flow-builder-services="flowBuilderServices" ... />
    	
    <webflow:flow-builder-services id="flowBuilderServices" conversion-service="defaultConversionService" ... />
    	
    <bean id="defaultConversionService" class="org.springframework.binding.convert.service.DefaultConversionService">
    	<constructor-arg ref="applicationConversionSevice"/>
    </bean>
				

Of course it is also possible to mix and match. Register new Spring 3 Formatter types through the "applicationConversionService". Register existing Spring Binding Converter types through the "defaultConversionService".

An important concept to understand is the difference between type converters and formatters.

Type converters in Spring 3, provided in org.springframework.core, are for general-purpose type conversion between any two object types. In addition to the most simple Converter type, two other interfaces are ConverterFactory and GenericConverter.

Formatters in Spring 3, provided in org.springframework.context, have the more specialized purpose of representing Objects as Strings. The Formatter interface extends the Printer and Parser interfaces for converting an Object to a String and turning a String into an Object.

Web developers will find the Formatter interface most relevant because it fits the needs of web applications for type conversion.

	Note
	An important point to be made is that Object-to-Object conversion is a generalization of the more specific Object-to-String conversion. In fact in the end Formatters are reigstered as GenericConverter types with Spring's GenericConversionService making them equal to any other converter.

One of the best features of the new type conversion is the ability to use annotations for a better control over formatting in a concise manner. Annotations can be placed on model attributes and on arguments of @Controller methods that are mapped to requests. Out of the box Spring provides two annotations NumberFormat and DateTimeFormat but you can create your own and have them registered along with the associated formatting logic. You can see examples of the DateTimeFormat annotation in the Spring Travel and in the Petcare along with other samples in the Spring Samples repository.

The DateTimeFormat annotation implies use of Joda Time. If that is present on the classpath the use of this annotation is enabled automatically. By default neither Spring MVC nor Web Flow register any other date formatters or converters. Therefore it is important for applications to register a custom formatter to specify the default way for printing and parsing dates. The DateTimeFormat annotation on the other hand provides more fine-grained control where it is necessary to deviate from the default.

For more information on working with Spring 3 type conversion and formatting please refer to the relevant sections of the Spring documentation.

Web Flow provides built-in support for the JSR-303 Bean Validation API building on equivalent support available in Spring MVC. To enable JSR-303 validation configure the flow-builder-services with Spring MVC's LocalValidatorFactoryBean:

<webflow:flow-registry flow-builder-services="flowBuilderServices" />

<webflow:flow-builder-services id="flowBuilderServices" validator="validator" />

<bean id="validator" class="org.springframework.validation.beanvalidation.LocalValidatorFactoryBean" />
			

With the above in place, the configured validator will be applied to all model attributes after data binding.

Note that JSR-303 bean validation and validation by convention (explained in the next section) are not mutually exclusive. In other words Web Flow will apply all available validation mechanisms.

There are two ways to perform model validation programatically. The first is to implement validation logic in your model object. The second is to implement an external Validator. Both ways provide you with a ValidationContext to record error messages and access information about the current user.

public class Booking {
    private Date checkinDate;
    private Date checkoutDate;
    ...
        
    public void validateEnterBookingDetails(ValidationContext context) {
        MessageContext messages = context.getMessageContext();
        if (checkinDate.before(today())) {
            messages.addMessage(new MessageBuilder().error().source("checkinDate").
                defaultText("Check in date must be a future date").build());
        } else if (!checkinDate.before(checkoutDate)) {
            messages.addMessage(new MessageBuilder().error().source("checkoutDate").
                defaultText("Check out date must be later than check in date").build());
        }
    }
}

					

<view-state id="enterBookingDetails" model="booking">
    <transition on="proceed" to="reviewBooking">
</view-state>
					

@Component
public class BookingValidator {
    public void validateEnterBookingDetails(Booking booking, ValidationContext context) {
        MessageContext messages = context.getMessageContext();
        if (booking.getCheckinDate().before(today())) {
            messages.addMessage(new MessageBuilder().error().source("checkinDate").
                defaultText("Check in date must be a future date").build());
        } else if (!booking.getCheckinDate().before(booking.getCheckoutDate())) {
            messages.addMessage(new MessageBuilder().error().source("checkoutDate").
                defaultText("Check out date must be later than check in date").build());
        }
    }
}
				

@Component
public class BookingValidator {
    public void validate(Booking booking, ValidationContext context) {
        //...
    }	
}
				

@Component
public class BookingValidator {
    public void validate(Booking booking, ValidationContext context) {
        //...
    }
    public void validateEnterBookingDetails(Booking booking, ValidationContext context) {
        //...
    }
}
				

A ValidationContext allows you to obtain a MessageContext to record messages during validation. It also exposes information about the current user, such as the signaled userEvent and the current user's Principal identity. This information can be used to customize validation logic based on what button or link was activated in the UI, or who is authenticated. See the API Javadocs for ValidationContext for more information.

A view-state transition can execute one or more actions before executing. These actions may return an error result to prevent the transition from exiting the current view-state. If an error result occurs, the view will re-render and should display an appropriate message to the user.

If the transition action invokes a plain Java method, the invoked method may return false to prevent the transition from executing. This technique can be used to handle exceptions thrown by service-layer methods. The example below invokes an action that calls a service and handles an exceptional situation:

<transition on="submit" to="bookingConfirmed">
    <evaluate expression="bookingAction.makeBooking(booking, messageContext)" />
</transition>
			

public class BookingAction {
   public boolean makeBooking(Booking booking, MessageContext context) {
       try {
           bookingService.make(booking);
           return true;
       } catch (RoomNotAvailableException e) {
           context.addMessage(new MessageBuilder().error().
               .defaultText("No room is available at this hotel").build());
           return false;
       }
   }
}
			

	Note
	When there is more than one action defined on a transition, if one returns an error result the remaining actions in the set will not be executed. If you need to ensure one transition action's result cannot impact the execution of another, define a single transition action that invokes a method that encapsulates all the action logic.

Use the flow's global-transitions element to create transitions that apply across all views. Global-transitions are often used to handle global menu links that are part of the layout.

<global-transitions>
    <transition on="login" to="login" />
    <transition on="logout" to="logout" />
</global-transitions>
			

From a view-state, transitions without targets can also be defined. Such transitions are called "event handlers":

<transition on="event">
    <!-- Handle event -->
</transition>
			

These event handlers do not change the state of the flow. They simply execute their actions and re-render the current view or one or more fragments of the current view.

Use the render element within a transition to request partial re-rendering of the current view after handling the event:

<transition on="next">
    <evaluate expression="searchCriteria.nextPage()" />
    <render fragments="searchResultsFragment" />            
</transition>
			

The fragments attribute should reference the id(s) of the view element(s) you wish to re-render. Specify multiple elements to re-render by separating them with a comma delimiter.

Such partial rendering is often used with events signaled by Ajax to update a specific zone of the view.

MessageContext context = ...
MessageBuilder builder = new MessageBuilder();
context.addMessage(builder.error().source("checkinDate")
    .defaultText("Check in date must be a future date").build());
context.addMessage(builder.warn().source("smoking")
    .defaultText("Smoking is bad for your health").build());
context.addMessage(builder.info()
    .defaultText("We have processed your reservation - thank you and enjoy your stay").build());
			

MessageContext context = ...
MessageBuilder builder = new MessageBuilder();
context.addMessage(builder.error().source("checkinDate").code("checkinDate.notFuture").build());
context.addMessage(builder.warn().source("smoking").code("notHealthy")
    .resolvableArg("smoking").build());			
context.addMessage(builder.info().code("reservationConfirmation").build());
			

Internationalized messages are defined in message bundles accessed by a Spring MessageSource. To create a flow-specific message bundle, simply define messages.properties file(s) in your flow's directory. Create a default messages.properties file and a .properties file for each additional Locale you need to support.

#messages.properties
checkinDate=Check in date must be a future date
notHealthy={0} is bad for your health
reservationConfirmation=We have processed your reservation - thank you and enjoy your stay
			

From within a view or a flow, you may also access message resources using the resourceBundle EL variable:

<h:outputText value="#{resourceBundle.reservationConfirmation}" />
			

There are several places where Web Flow itself will generate messages to display to the user. One important place this occurs is during view-to-model data binding. When a binding error occurs, such as a type conversion error, Web Flow will map that error to a message retrieved from your resource bundle automatically. To lookup the message to display, Web Flow tries resource keys that contain the binding error code and target property name.

As an example, consider a binding to a checkinDate property of a Booking object. Suppose the user typed in a alphabetic string. In this case, a type conversion error will be raised. Web Flow will map the 'typeMismatch' error code to a message by first querying your resource bundle for a message with the following key:

booking.checkinDate.typeMismatch
			

The first part of the key is the model class's short name. The second part of the key is the property name. The third part is the error code. This allows for the lookup of a unique message to display to the user when a binding fails on a model property. Such a message might say:

booking.checkinDate.typeMismatch=The check in date must be in the format yyyy-mm-dd.
			

If no such resource key can be found of that form, a more generic key will be tried. This key is simply the error code. The field name of the property is provided as a message argument.

typeMismatch=The {0} field is of the wrong type.
			

Set the history attribute to discard to prevent backtracking to a view:

<transition on="cancel" to="bookingCancelled" history="discard">
			

Set the history attribute to invalidate to prevent backtracking to a view as well all previously displayed views:

<transition on="confirm" to="bookingConfirmed" history="invalidate">
			

<evaluate expression="pojoAction.method(flowRequestContext)" />	
        	

public class PojoAction {
    public String method(RequestContext context) {
        ... 
    }
}
			

<evaluate expression="customAction" />	
        	

public class CustomAction implements Action {
    public Event execute(RequestContext context) {
        ... 
    }
}
			

<evaluate expression="multiAction.actionMethod1" />
	
        	

public class CustomMultiAction extends MultiAction {
    public Event actionMethod1(RequestContext context) {
        ... 
    }

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

    ...
}
			

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.

<evaluate expression="bookingAction.makeBooking(booking, flowRequestContext)" />	
        	

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";
       }
   }
}
			

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 Event ${methodName}(RequestContext), providing stronger type safety, while a POJO action allows for more freedom.

<evaluate expression="bookingAction.makeBooking" />	
        	

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();
       }
   }
}
			

The following example shows an action that creates a new Booking object by invoking a method on a service:

<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-2.0.xsd">

    <input name="hotelId" />

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

</flow>
			

The following example shows a state entry action that sets the special fragments variable that causes the view-state to render a partial fragment of its view:

<view-state id="changeSearchCriteria" view="enterSearchCriteria.xhtml" popup="true">
    <on-entry>
        <render fragments="hotelSearchForm" />
    </on-entry>
</view-state>
			

The following example shows a state exit action that releases a lock on a record being edited:

<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>
			

The following example shows the equivalent object locking behavior using flow start and end actions:

<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-2.0.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>
			

The following example shows a render action that loads a list of hotels to display before the view is rendered:

<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>
			

The following example shows a transition action adds a subflow outcome event attribute to a collection:

<subflow-state id="addGuest" subflow="createGuest">
    <transition on="guestCreated" to="reviewBooking">
        <evaluate expression="booking.guestList.add(currentEvent.attributes.newGuest)" />  
    </transition>
</subfow-state>
			

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.

<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>
			

In this example, the flow will transition to showResults when thingTwo completes successfully.

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.

<view-state id="reviewItinerary">
    <transition on="print">
        <evaluate expression="printBoardingPassAction" />
    </transition>
</view-state>
			

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();
    }
}
			

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.

Another common task is to use Web Flow to handle multipart file uploads in combination with Spring MVC's MultipartResolver. Once the resolver is set up correctly as described here and the submitting HTML form is configured with enctype="multipart/form-data", you can easily handle the file upload in a transition action.

	Note
	The file upload example below below is not relevant when using Web Flow with JSF. See Section 13.8.5, “Handling File Uploads with JSF” for details of how to upload files using JSF.

Given a form such as:

<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>
			

and a backing object for handling the upload such as:

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;
    } 
}
			

you can process the upload using a transition action as in the following example:

<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>
			

The MultipartFile will be bound to the FileUploadHandler bean as part of the normal form binding process so that it will be available to process during the execution of the transition action.

The attributes attribute is a comma separated list of Spring Security authorization attributes. Often, these are specific security roles. The attributes are compared against the user's granted attributes by a Spring Security access decision manager.

<secured attributes="ROLE_USER" />
			

By default, a role based access decision manager is used to determine if the user is allowed access. This will need to be overridden if your application is not using authorization roles.

There are two types of matching available: any and all. Any, allows access if at least one of the required security attributes is granted to the user. All, allows access only if each of the required security attributes are granted to the user.

<secured attributes="ROLE_USER, ROLE_ANONYMOUS" match="any" />
			

This attribute is optional. If not defined, the default value is any.

The match attribute will only be respected if the default access decision manager is used.

If your application is using authorities that are not role based, you will need to configure a custom AccessDecisionManager. You can override the default decision manager by setting the accessDecisionManager property on the security listener. Please consult the Spring Security reference documentation to learn more about decision managers.

<bean id="securityFlowExecutionListener"
      class="org.springframework.webflow.security.SecurityFlowExecutionListener">
    <property name="accessDecisionManager" ref="myCustomAccessDecisionManager" />
</bean>
			

The Spring configuration defines http specifics (such as protected URLs and login/logout mechanics) and the authentication-provider. For the sample applications, a local authentication provider is configured.

<security:http auto-config="true">
    <security:form-login login-page="/spring/login" 
                         login-processing-url="/spring/loginProcess"
                         default-target-url="/spring/main" 
                         authentication-failure-url="/spring/login?login_error=1" />  
    <security:logout logout-url="/spring/logout" logout-success-url="/spring/logout-success" />
</security:http>

<security:authentication-provider>
    <security:password-encoder hash="md5" />
    <security:user-service>
        <security:user name="keith" password="417c7382b16c395bc25b5da1398cf076" 
                       authorities="ROLE_USER,ROLE_SUPERVISOR" />
        <security:user name="erwin" password="12430911a8af075c6f41c6976af22b09" 
                       authorities="ROLE_USER,ROLE_SUPERVISOR" />
        <security:user name="jeremy" password="57c6cbff0d421449be820763f03139eb" 
                       authorities="ROLE_USER" />
        <security:user name="scott" password="942f2339bf50796de535a384f0d1af3e" 
                       authorities="ROLE_USER" />
    </security:user-service>
</security:authentication-provider>
			

In the web.xml file, a filter is defined to intercept all requests. This filter will listen for login/logout requests and process them accordingly. It will also catch AccesDeniedExceptions and redirect the user to the login page.

<filter>
    <filter-name>springSecurityFilterChain</filter-name>
    <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
</filter>

<filter-mapping>
    <filter-name>springSecurityFilterChain</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>
			

Flow level inheritance is defined by the parent attribute on the flow element. The attribute contains a comma separated list of flow identifiers to inherit from. The child flow will inherit from each parent in the order it is listed adding elements and content to the resulting flow. The resulting flow from the first merge will be considered the child in the second merge, and so on.

<flow parent="common-transitions, common-states">
			

State level inheritance is similar to flow level inheritance, except only one state inherits from the parent, instead of the entire flow.

Unlike flow inheritance, only a single parent is allowed. Additionally, the identifier of the flow state to inherit from must also be defined. The identifiers for the flow and the state within that flow are separated by a #.

The parent and child states must be of the same type. For instance a view-state cannot inherit from an end-state, only another view-state.

<view-state id="child-state" parent="parent-flow#parent-view-state">
			

If the elements are of the same type and their keyed attribute are identical, the content of the parent element will be merged with the child element. The merge algorithm will continue to merge each sub-element of the merging parent and child. Otherwise the parent element is added as a new element to the child.

In most cases, elements from a parent flow that are added will be added after elements in the child flow. Exceptions to this rule include action elements (evaluate, render and set) which will be added at the beginning. This allows for the results of parent actions to be used by child actions.

Mergeable elements are:

Non-mergeable elements are:

Register your flows in a FlowRegistry:

<webflow:flow-registry id="flowRegistry">
    <webflow:flow-location path="/WEB-INF/flows/booking/booking.xml" />
</webflow:flow-registry>
			

Deploy a FlowExecutor, the central service for executing flows:

<webflow:flow-executor id="flowExecutor" />
			

See the Spring MVC and Spring Faces sections of this guide on how to integrate the Web Flow system with the MVC and JSF environment, respectively.

Use the location element to specify paths to flow definitions to register. By default, flows will be assigned registry identifiers equal to their filenames minus the file extension, unless a registry bath path is defined.

<webflow:flow-location path="/WEB-INF/flows/booking/booking.xml" />
			

Specify an id to assign a custom registry identifier to a flow:

<webflow:flow-location path="/WEB-INF/flows/booking/booking.xml" id="bookHotel" />
			

Use the flow-definition-attributes element to assign custom meta-attributes to a registered flow:

<webflow:flow-location path="/WEB-INF/flows/booking/booking.xml">
    <webflow:flow-definition-attributes>
        <webflow:attribute name="caption" value="Books a hotel" />
    </webflow:flow-definition-attributes>
</webflow:flow-location>
			

Use the flow-location-patterns element to register flows that match a specific resource location pattern:

<webflow:flow-location-pattern value="/WEB-INF/flows/**/*-flow.xml" />
			

Use the base-path attribute to define a base location for all flows in the application. All flow locations are then relative to the base path. The base path can be a resource path such as '/WEB-INF' or a location on the classpath like 'classpath:org/springframework/webflow/samples'.

<webflow:flow-registry id="flowRegistry" base-path="/WEB-INF">
    <webflow:flow-location path="/hotels/booking/booking.xml" />
</webflow:flow-registry>
			

With a base path defined, the algorithm that assigns flow identifiers changes slightly. Flows will now be assigned registry identifiers equal to the the path segment between their base path and file name. For example, if a flow definition is located at '/WEB-INF/hotels/booking/booking-flow.xml' and the base path is '/WEB-INF' the remaining path to this flow is 'hotels/booking' which becomes the flow id.

	Directory per flow definition
	Recall it is a best practice to package each flow definition in a unique directory. This improves modularity, allowing dependent resources to be packaged with the flow definition. It also prevents two flows from having the same identifiers when using the convention.

If no base path is not specified or if the flow definition is directly on the base path, flow id assignment from the filename (minus the extension) is used. For example, if a flow definition file is 'booking.xml', the flow identifier is simply 'booking'.

Location patterns are particularly powerful when combined with a registry base path. Instead of the flow identifiers becoming '*-flow', they will be based on the directory path. For example:

<webflow:flow-registry id="flowRegistry" base-path="/WEB-INF">
    <webflow:flow-location-pattern value="/**/*-flow.xml" />
</webflow:flow-registry>
			

In the above example, suppose you had flows located in /user/login, /user/registration, /hotels/booking, and /flights/booking directories within WEB-INF, you'd end up with flow ids of user/login, user/registration, hotels/booking, and flights/booking, respectively.

Use the parent attribute to link two flow registries together in a hierarchy. When the child registry is queried, if it cannot find the requested flow it will delegate to its parent.

<!-- my-system-config.xml -->
<webflow:flow-registry id="flowRegistry" parent="sharedFlowRegistry">
    <webflow:flow-location path="/WEB-INF/flows/booking/booking.xml" />
</webflow:flow-registry>

<!-- shared-config.xml -->
<webflow:flow-registry id="sharedFlowRegistry">
    <!-- Global flows shared by several applications -->
</webflow:flow-registry>
			

Use the flow-builder-services attribute to customize the services and settings used to build flows in a flow-registry. If no flow-builder-services tag is specified, the default service implementations are used. When the tag is defined, you only need to reference the services you want to customize.

<webflow:flow-registry id="flowRegistry" flow-builder-services="flowBuilderServices">
    <webflow:flow-location path="/WEB-INF/flows/booking/booking.xml" />
</webflow:flow-registry>

<webflow:flow-builder-services id="flowBuilderServices" />
			

The configurable services are the conversion-service, expression-parser, and view-factory-creator. These services are configured by referencing custom beans you define. For example:

<webflow:flow-builder-services id="flowBuilderServices"
    conversion-service="conversionService"
    expression-parser="expressionParser"
    view-factory-creator="viewFactoryCreator" />

<bean id="conversionService" class="..." />
<bean id="expressionParser" class="..." />
<bean id="viewFactoryCreator" class="..." />
			

Use the flow-execution-listeners element to register listeners that observe the lifecycle of flow executions:

<webflow:flow-execution-listeners>
    <webflow:listener ref="securityListener"/>
    <webflow:listener ref="persistenceListener"/>
</webflow:flow-execution-listeners>
			

You may also configure a listener to observe only certain flows:

<webflow:listener ref="securityListener" criteria="securedFlow1,securedFlow2"/>
			

Use the flow-execution-repository element to tune flow execution persistence settings:

<webflow:flow-executor id="flowExecutor" flow-registry="flowRegistry">
    <webflow:flow-execution-repository max-executions="5" max-execution-snapshots="30" />
</webflow:flow-executor>
			

max-executions

Tune the max-executions attribute to place a cap on the number of flow executions that can be created per user session. When the maximum number of executions is exceeded, the oldest execution is removed.

	Note
	The max-executions attribute is per user session, i.e. it works across instances of any flow definition.

max-execution-snapshots

Tune the max-execution-snapshots attribute to place a cap on the number of history snapshots that can be taken per flow execution. To disable snapshotting, set this value to 0. To enable an unlimited number of snapshots, set this value to -1.

	Note
	History snapshots enable browser back button support. When snapshotting is disabled pressing the browser back button will not work. It will result in using an execution key that points to a snapshot that has not be recorded.

The first step to dispatching requests to flows is to enable flow handling within Spring MVC. To this, install the FlowHandlerAdapter:

<!-- Enables FlowHandler URL mapping -->
<bean class="org.springframework.webflow.mvc.servlet.FlowHandlerAdapter">
    <property name="flowExecutor" ref="flowExecutor" />
</bean>
			

Once flow handling is enabled, the next step is to map specific application resources to your flows. The simplest way to do this is to define a FlowHandlerMapping:

<!-- Maps request paths to flows in the flowRegistry;
     e.g. a path of /hotels/booking looks for a flow with id "hotels/booking" -->		
<bean class="org.springframework.webflow.mvc.servlet.FlowHandlerMapping">
    <property name="flowRegistry" ref="flowRegistry"/>
    <property name="order" value="0"/>
</bean>
			

Configuring this mapping allows the Dispatcher to map application resource paths to flows in a flow registry. For example, accessing the resource path /hotels/booking would result in a registry query for the flow with id hotels/booking. If a flow is found with that id, that flow will handle the request. If no flow is found, the next handler mapping in the Dispatcher's ordered chain will be queried or a "noHandlerFound" response will be returned.

When a valid flow mapping is found, the FlowHandlerAdapter figures out whether to start a new execution of that flow or resume an existing execution based on information present the HTTP request. There are a number of defaults related to starting and resuming flow executions the adapter employs:

Consult the API documentation for FlowHandlerAdapter for more information. You may override these defaults by subclassing or by implementing your own FlowHandler, discussed in the next section.

A common interaction pattern between Spring MVC And Web Flow is for a Flow to redirect to a @Controller when it ends. FlowHandlers allow this to be done without coupling the flow definition itself with a specific controller URL. An example FlowHandler that redirects to a Spring MVC Controller is shown below:

public class BookingFlowHandler extends AbstractFlowHandler {
    public String handleExecutionOutcome(FlowExecutionOutcome outcome,
                                         HttpServletRequest request, HttpServletResponse response) {
        if (outcome.getId().equals("bookingConfirmed")) {
            return "/booking/show?bookingId=" + outcome.getOutput().get("bookingId");
        } else {
            return "/hotels/index";
        }
    }
}
			

Since this handler only needs to handle flow execution outcomes in a custom manner, nothing else is overridden. The bookingConfirmed outcome will result in a redirect to show the new booking. Any other outcome will redirect back to the hotels index page.

To install a custom FlowHandler, simply deploy it as a bean. The bean name must match the id of the flow the handler should apply to.

<bean name="hotels/booking" class="org.springframework.webflow.samples.booking.BookingFlowHandler" />
			

With this configuration, accessing the resource /hotels/booking will launch the hotels/booking flow using the custom BookingFlowHandler. When the booking flow ends, the FlowHandler will process the flow execution outcome and redirect to the appropriate controller.

A FlowHandler handling a FlowExecutionOutcome or FlowException returns a String to indicate the resource to redirect to after handling. In the previous example, the BookingFlowHandler redirects to the booking/show resource URI for bookingConfirmed outcomes, and the hotels/index resource URI for all other outcomes.

By default, returned resource locations are relative to the current servlet mapping. This allows for a flow handler to redirect to other Controllers in the application using relative paths. In addition, explicit redirect prefixes are supported for cases where more control is needed.

The explicit redirect prefixes supported are:

These same redirect prefixes are also supported within a flow definition when using the externalRedirect: directive in conjunction with a view-state or end-state; for example, view="externalRedirect:http://springframework.org"

The example below shows two buttons on the same form that signal proceed and cancel events when clicked, respectively.

<input type="submit" name="_eventId_proceed" value="Proceed" />
<input type="submit" name="_eventId_cancel" value="Cancel" />		
			

When a button is pressed Web Flow finds a request parameter name beginning with _eventId_ and treats the remaining substring as the event id. So in this example, submitting _eventId_proceed becomes proceed. This style should be considered when there are several different events that can be signaled from the same form.

The example below shows a form that signals the proceed event when submitted:

<input type="submit" value="Proceed" />
<input type="hidden" name="_eventId" value="proceed" />	
			

Here, Web Flow simply detects the special _eventId parameter and uses its value as the event id. This style should only be considered when there is one event that can be signaled on the form.

The example below shows a link that signals the cancel event when activated:

<a href="${flowExecutionUrl}&_eventId=cancel">Cancel</a>		
			

Firing an event results in a HTTP request being sent back to the server. On the server-side, the flow handles decoding the event from within its current view-state. How this decoding process works is specific to the view implementation. Recall a Spring MVC view implementation simply looks for a request parameter named _eventId. If no _eventId parameter is found, the view will look for a parameter that starts with _eventId_ and will use the remaining substring as the event id. If neither cases exist, no flow event is triggered.

By default Web Flow does a client-side redirect upon entering every view state. However if you remain in the same view state -- for example a transition without a "to" attribute -- during an Ajax request there will not be a client-side redirect. This behavior should be quite familiar to Spring Web Flow 2 users. It is appropriate for a top-level flow that supports the browser back button while still taking advantage of Ajax and partial rendering for use cases where you remain in the same view such as form validation, paging trough search results, and others. However transitions to a new view state are always followed with a client-side redirect. That makes it impossible to embed a flow on a page or within a modal dialog and execute more than one view state without causing a full-page refresh. Hence if your use case requires embedding a flow you can launch it in "embedded" mode.

If you'd like to see examples of a flow embedded on a page and within a modal dialog please refer to the webflow-showcase project. You can check out the source code locally, build it as you would a Maven project, and import it into Eclipse:

cd some-directory
svn co https://src.springframework.org/svn/spring-samples/webflow-showcase
cd webflow-showcase
mvn package
# import into Eclipse

The key interface for integrating various Ajax libraries with the Ajax-aware behavior of Web Flow (such as not redirecting for a partial page update) is org.springframework.js.AjaxHandler. A SpringJavascriptAjaxHandler is configured by default that is able to detect an Ajax request submitted via the Spring JS client-side API and can respond appropriately in the case where a redirect is required. In order to integrate a different Ajax library (be it a pure JavaScript library, or a higher-level abstraction such as an Ajax-capable JSF component library), a custom AjaxHandler can be injected into the FlowHandlerAdapter or FlowController.

In order to handle Ajax requests with Spring MVC controllers, all that is needed is the configuration of the provided Spring MVC extensions in your Spring application context for rendering the partial response (note that these extensions require the use of Tiles for templating):

<bean id="tilesViewResolver" class="org.springframework.js.ajax.AjaxUrlBasedViewResolver">
    <property name="viewClass" value="org.springframework.webflow.mvc.view.FlowAjaxTilesView"/>
</bean>
            

This configures the AjaxUrlBasedViewResolver which in turn interprets Ajax requests and creates FlowAjaxTilesView objects to handle rendering of the appropriate fragments. Note that FlowAjaxTilesView is capable of handling the rendering for both Web Flow and pure Spring MVC requests. The fragments correspond to individual attributes of a Tiles view definition. For example, take the following Tiles view definition:

<definition name="hotels/index" extends="standardLayout">
    <put-attribute name="body" value="index.body" />
</definition>

<definition name="index.body" template="/WEB-INF/hotels/index.jsp">
    <put-attribute name="hotelSearchForm" value="/WEB-INF/hotels/hotelSearchForm.jsp" />
    <put-attribute name="bookingsTable" value="/WEB-INF/hotels/bookingsTable.jsp" />
</definition>
            

An Ajax request could specify the "body", "hotelSearchForm" or "bookingsTable" to be rendered as fragments in the request.

Spring Web Flow handles the optional rendering of fragments directly in the flow definition language through use of the render element. The benefit of this approach is that the selection of fragments is completely decoupled from client-side code, such that no special parameters need to be passed with the request the way they currently must be with the pure Spring MVC controller approach. For example, if you wanted to render the "hotelSearchForm" fragment from the previous example Tiles view into a rich Javascript popup:

<view-state id="changeSearchCriteria" view="enterSearchCriteria.xhtml" popup="true">
    <on-entry>
        <render fragments="hotelSearchForm" />
    </on-entry>
    <transition on="search" to="reviewHotels">
        <evaluate expression="searchCriteria.resetPage()"/>
    </transition>
</view-state>                
            

When using the JSF 1.2 Spring Faces component library, you also need to configure a servlet for serving CSS and JavaScript resources. This servlet must be mapped to /resources/* in order for the URL's rendered by the components to function correctly.

<!-- Serves static resource content from .jar files such as spring-faces.jar -->
<servlet>
    <servlet-name>Resource Servlet</servlet-name>
    <servlet-class>org.springframework.js.resource.ResourceServlet</servlet-class>
    <load-on-startup>0</load-on-startup>
</servlet>
        
<!-- Map all /resources requests to the Resource Servlet for handling -->
<servlet-mapping>
    <servlet-name>Resource Servlet</servlet-name>
    <url-pattern>/resources/*</url-pattern>
</servlet-mapping>
        

For optimal page-loading performance use the Spring Faces components includeStyles and includeScripts. These components will eagerly load the necessary CSS stylesheets and JavaScript files at the position they are placed in your JSF view template. In accordance with the recommendations of the Yahoo Performance Guildlines, these two tags should be placed in the head section of any page that uses the Spring Faces components. For example:

 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<f:view xmlns="http://www.w3.org/1999/xhtml"
      xmlns:ui="http://java.sun.com/jsf/facelets"
      xmlns:f="http://java.sun.com/jsf/core"
	  xmlns:c="http://java.sun.com/jstl/core"
	  xmlns:sf="http://www.springframework.org/tags/faces"
	  contentType="text/html" encoding="UTF-8">
<html>
<head>
	<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
	<title>Hotel Booking Sample Application</title>
	
	<sf:includeStyles />
	<sf:includeScripts />
	
	<ui:insert name="headIncludes"/>
</head>
...
</html>
</f:view>
		

This shows the opening of a typical Facelets XHTML layout template that uses these components to force the loading of the needed CSS and JavaScript resources at the ideal position.

The includeStyles component includes the necessary resources for the Dojo widget theme. By default, it includes the resources for the "tundra" theme. An alternate theme may be selected by setting the optional "theme" and "themePath" attributes on the includeStyles component. For example:

 
<sf:includeStyles themePath="/styles/" theme="foobar"/>

		

will try to load a CSS stylesheet at "/styles/foobar/foobar.css" using the Spring JavaScript ResourceServlet.

The easiest and most natural way to declare and manage the model is through the use of flow variables. You can declare these variables at the beginning of the flow:

<var name="searchCriteria" class="com.mycompany.myapp.hotels.search.SearchCriteria"/>
            

and then reference this variable in one of the flow's JSF view templates through EL:

<h:inputText id="searchString" value="#{searchCriteria.searchString}"/>
            

Note that you do not need to prefix the variable with its scope when referencing it from the template (though you can do so if you need to be more specific). As with standard JSF beans, all available scopes will be searched for a matching variable, so you could change the scope of the variable in your flow definition without having to modify the EL expressions that reference it.

You can also define view instance variables that are scoped to the current view and get cleaned up automatically upon transitioning to another view. This is quite useful with JSF as views are often constructed to handle multiple in-page events across many requests before transitioning to another view.

To define a view instance variable, you can use the var element inside a view-state definition:

<view-state id="enterSearchCriteria"> 
    <var name="searchCriteria" class="com.mycompany.myapp.hotels.search.SearchCriteria"/> 
</view-state>
            

Though defining autowired flow instance variables provides nice modularization and readability, occasions may arise where you want to utilize the other capabilities of the Spring container such as AOP. In these cases, you can define a bean in your Spring ApplicationContext and give it a specific web flow scope:

<bean id="searchCriteria" class="com.mycompany.myapp.hotels.search.SearchCriteria" scope="flow"/>
            

The major difference with this approach is that the bean will not be fully initialized until it is first accessed via an EL expression. This sort of lazy instantiation via EL is quite similar to how JSF managed beans are typically allocated.

The need to initialize the model before view rendering (such as by loading persistent entities from a database) is quite common, but JSF by itself does not provide any convenient hooks for such initialization. The flow definition language provides a natural facility for this through its Actions . Spring Web Flow provides some extra conveniences for converting the outcome of an action into a JSF-specific data structure. For example:

 
<on-render>
    <evaluate expression="bookingService.findBookings(currentUser.name)" 
              result="viewScope.bookings" result-type="dataModel" />
</on-render>
            

This will take the result of the bookingService.findBookings method an wrap it in a custom JSF DataModel so that the list can be used in a standard JSF DataTable component:

 
<h:dataTable id="bookings" styleClass="summary" value="#{bookings}" var="booking" 
             rendered="#{bookings.rowCount > 0}">
    <h:column>
        <f:facet name="header">Name</f:facet>
        #{booking.hotel.name}
    </h:column>                   
    <h:column>
    <f:facet name="header">Confirmation number</f:facet>
        #{booking.id}
        </h:column>
    <h:column>
        <f:facet name="header">Action</f:facet>
        <h:commandLink id="cancel" value="Cancel" action="cancelBooking" />
    </h:column>
</h:dataTable>
            

In the example above result-type="dataModel" results in the wrapping of List<Booking> with custom DataModel type. The custom DataModel provides extra conveniences such as being serializable for storage beyond request scope as well as access to the currently selected row in EL expressions. For example, on postback from a view where the action event was fired by a component within a DataTable, you can take action on the selected row's model instance:

<transition on="cancelBooking">
    <evaluate expression="bookingService.cancelBooking(bookings.selectedRow)" />            
</transition>
            

Spring Web Flow provides two custom DataModel types: OneSelectionTrackingListDataModel and ManySelectionTrackingListDataModel. As the names indicate they keep track of one or multiple selected rows. This is done with the help of a SelectionTrackingActionListener listener, which responds to JSF action events and invokes the appopriate methods on the SelectinAware data models to record the currently clicked row.

To understand how this is configured, keep in mind the FacesConversionService registers a DataModelConverter against the alias "dataModel" on startup. When result-type="dataModel" is used in a flow definition it causes the DataModelConverter to be used. The converter then wraps the given List with an instance of OneSelectionTrackingListDataModel. To use the ManySelectionTrackingListDataModel you will need to register your own custom converter.

A simple but common case in JSF is the need to signal an event that causes manipulation of the model in some way and then redisplays the same view to reflect the changed state of the model. The flow definition language has special support for this in the transition element.

A good example of this is a table of paged list results. Suppose you want to be able to load and display only a portion of a large result list, and allow the user to page through the results. The initial view-state definition to load and display the list would be:

 
<view-state id="reviewHotels">
    <on-render>
        <evaluate expression="bookingService.findHotels(searchCriteria)" 
                  result="viewScope.hotels" result-type="dataModel" />
    </on-render>
</view-state>
            

You construct a JSF DataTable that displays the current hotels list, and then place a "More Results" link below the table:

 
<h:commandLink id="nextPageLink" value="More Results" action="next"/>
            

This commandLink signals a "next" event from its action attribute. You can then handle the event by adding to the view-state definition:

 
<view-state id="reviewHotels">
    <on-render>
        <evaluate expression="bookingService.findHotels(searchCriteria)" 
            result="viewScope.hotels" result-type="dataModel" />
    </on-render>
    <transition on="next">
        <evaluate expression="searchCriteria.nextPage()" />
    </transition>
</view-state>
            

Here you handle the "next" event by incrementing the page count on the searchCriteria instance. The on-render action is then called again with the updated criteria, which causes the next page of results to be loaded into the DataModel. The same view is re-rendered since there was no to attribute on the transition element, and the changes in the model are reflected in the view.

The next logical level beyond in-page events are events that require navigation to another view, with some manipulation of the model along the way. Achieving this with pure JSF would require adding a navigation rule to faces-config.xml and likely some intermediary Java code in a JSF managed bean (both tasks requiring a re-deploy). With the flow defintion language, you can handle such a case concisely in one place in a quite similar way to how in-page events are handled.

Continuing on with our use case of manipulating a paged list of results, suppose we want each row in the displayed DataTable to contain a link to a detail page for that row instance. You can add a column to the table containing the following commandLink component:

<h:commandLink id="viewHotelLink" value="View Hotel" action="select"/>
            

This raises the "select" event which you can then handle by adding another transition element to the existing view-state :

 
<view-state id="reviewHotels">
    <on-render>
        <evaluate expression="bookingService.findHotels(searchCriteria)" 
            result="viewScope.hotels" result-type="dataModel" />
    </on-render>
    <transition on="next">
        <evaluate expression="searchCriteria.nextPage()" />
    </transition>
    <transition on="select" to="reviewHotel">
            <set name="flowScope.hotel" value="hotels.selectedRow" />
    </transition>
</view-state>
            

Here the "select" event is handled by pushing the currently selected hotel instance from the DataTable into flow scope, so that it may be referenced by the "reviewHotel" view-state .

JSF provides useful facilities for validating input at field-level before changes are applied to the model, but when you need to then perform more complex validation at the model-level after the updates have been applied, you are generally left with having to add more custom code to your JSF action methods in the managed bean. Validation of this sort is something that is generally a responsibility of the domain model itself, but it is difficult to get any error messages propagated back to the view without introducing an undesirable dependency on the JSF API in your domain layer.

With Web Flow, you can utilize the generic and low-level MessageContext in your business code and any messages added there will then be available to the FacesContext at render time.

For example, suppose you have a view where the user enters the necessary details to complete a hotel booking, and you need to ensure the Check In and Check Out dates adhere to a given set of business rules. You can invoke such model-level validation from a transition element:

 
<view-state id="enterBookingDetails">
    <transition on="proceed" to="reviewBooking">
        <evaluate expression="booking.validateEnterBookingDetails(messageContext)" />
    </transition>
</view-state>
            

Here the "proceed" event is handled by invoking a model-level validation method on the booking instance, passing the generic MessageContext instance so that messages may be recorded. The messages can then be displayed along with any other JSF messages with the h:messages component,

JSF 2 provides built-in support for sending Ajax requests and performing partial processing and rendering on the server-side. You can specify a list of id's for partial rendering through the <f:ajax> facelets tag.

In Spring Web Flow you also have the option to specify the ids to use for partial rendering on the server side with the render action:

<view-state id="reviewHotels">
    <on-render>
        <evaluate expression="bookingService.findHotels(searchCriteria)" 
                  result="viewScope.hotels" result-type="dataModel" />
    </on-render>
    <transition on="next">
        <evaluate expression="searchCriteria.nextPage()" />
        <render fragments="hotels:searchResultsFragment" />
    </transition>
</view-state>
      

Most JSF component providers include some form of 'file upload' component. Generally when working with these components JSF must take complete control of parsing multi-part requests and Spring MVC's MultipartResolver cannot be used.

Spring Web Flow has been tested with file upload components from PrimeFaces and RichFaces. Check the documentation of your JSF component library for other providers to see how to configure file upload.

<filter>
	<filter-name>PrimeFaces FileUpload Filter</filter-name>
	<filter-class>org.primefaces.webapp.filter.FileUploadFilter</filter-class>
</filter>
<filter-mapping>
	<filter-name>PrimeFaces FileUpload Filter</filter-name>
	<servlet-name>Spring MVC Dispatcher Servlet</servlet-name>
</filter-mapping>
			

<rich:fileUpload id="upload"
	fileUploadListener="#{fileUploadBean.listener}"
	acceptedTypes="jpg, gif, png, bmp">
</rich:fileUpload>

public class FileUploadBean {

	public void listener(FileUploadEvent event) throws Exception{
		FacesContext.getCurrentInstance().getPartialViewContext().processPartial(PhaseId.RENDER_RESPONSE);
		ExternalContextHolder.getExternalContext().recordResponseComplete();
		UploadedFile file = event.getUploadedFile();
		// Do something with the file
	}
}

For JSF 1.2 the Spring Faces UICommand components have the ability to do Ajax-based partial view updates. These components degrade gracefully so that the flow will still be fully functional by falling back to full page refreshes if a user with a less capable browser views the page.

Revisiting the earlier example with the paged table, you can change the "More Results" link to use an Ajax request by replacing the standard commandButton with the Spring Faces component version (note that the Spring Faces command components use Ajax by default, but they can alternately be forced to use a normal form submit by setting ajaxEnabled="false" on the component):

            
<sf:commandLink id="nextPageLink" value="More Results" action="next" />
            

This event is handled just as in the non-Ajax case with the transition element, but now you will add a special render action that specifies which portions of the component tree need to be re-rendered:

<view-state id="reviewHotels">
    <on-render>
        <evaluate expression="bookingService.findHotels(searchCriteria)" 
                  result="viewScope.hotels" result-type="dataModel" />
    </on-render>
    <transition on="next">
        <evaluate expression="searchCriteria.nextPage()" />
        <render fragments="hotels:searchResultsFragment" />
    </transition>
</view-state>
            

The fragments="hotels:searchResultsFragment" is an instruction that will be interpreted at render time, such that only the component with the JSF clientId "hotels:searchResultsFragment" will be rendered and returned to the client. This fragment will then be automatically replaced in the page. The fragments attribute can be a comma-delimited list of ids, with each id representing the root node of a subtree (meaning the root node and all of its children) to be rendered. If the "next" event is fired in a non-Ajax request (i.e., if JavaScript is disabled on the client), the render action will be ignored and the full page will be rendered as normal.

In addition to the Spring Faces commandLink component, there is a corresponding commandButton component with the same functionality. There is also a special ajaxEvent component that will raise a JSF action even in response to any client-side DOM event. See the Spring Faces tag library docs for full details.

An additional built-in feature when using the Spring Faces Ajax-enabled components is the ability to have the response rendered inside a rich modal popup widget by setting popup="true" on a view-state .

<view-state id="changeSearchCriteria" view="enterSearchCriteria.xhtml" popup="true">
    <on-entry>
        <render fragments="hotelSearchFragment" />
    </on-entry>
    <transition on="search" to="reviewHotels">
        <evaluate expression="searchCriteria.resetPage()"/>
    </transition>
</view-state>
            

If the "changeSearchCriteria" view-state is reached as the result of an Ajax-request, the result will be rendered into a rich popup. If JavaScript is unavailable, the request will be processed with a full browser refresh, and the "changeSearchCriteria" view will be rendered as normal.

Simple client-side text validation can be applied with the clientTextValidator component:

 
<sf:clientTextValidator required="true">
    <h:inputText id="creditCardName" value="#{booking.creditCardName}" required="true"/>
</sf:clientTextValidator>
            

This will apply client-side required validation to the child inputText component, giving the user a clear indicator if the field is left blank.

Simple client-side numeric validation can be applied with the clientNumberValidator component:

 
<sf:clientTextValidator required="true" regExp="[0-9]{16}" 
                        invalidMessage="A 16-digit credit card number is required.">
    <h:inputText id="creditCard" value="#{booking.creditCard}" required="true"/>
</sf:clientTextValidator>
            

This will apply client-side validation to the child inputText component, giving the user a clear indicator if the field is left blank, is not numeric, or does not match the given regular expression.

Simple client-side date validation with a rich calendar popup can be applied with the clientDateValidator component:

 
<sf:clientDateValidator required="true" >
    <h:inputText id="checkinDate" value="#{booking.checkinDate}" required="true">
        <f:convertDateTime pattern="yyyy-MM-dd" timeZone="EST"/>
    </h:inputText>
</sf:clientDateValidator>
            

This will apply client-side validation to the child inputText component, giving the user a clear indicator if the field is left blank or is not a valid date.

The validateAllOnClick component can be used to intercept the "onclick" event of a child component and suppress the event if all client-side validations do not pass.

 
<sf:validateAllOnClick>
    <sf:commandButton id="proceed" action="proceed" processIds="*" value="Proceed"/>&#160;
</sf:validateAllOnClick>
            

This will prevent the form from being submitted when the user clicks the "proceed" button if the form is invalid. When the validations are executed, the user is given clear and immediate indicators of the problems that need to be corrected.

To use the Rich Faces component library with Spring Web Flow, the following filter configuration is needed in web.xml (in addition to the other typical configuration already shown):

 
<filter> 
    <display-name>RichFaces Filter</display-name> 
    <filter-name>richfaces</filter-name> 
    <filter-class>org.ajax4jsf.Filter</filter-class> 
</filter> 

<filter-mapping> 
    <filter-name>richfaces</filter-name> 
    <servlet-name>Spring Web MVC Dispatcher Servlet</servlet-name>
    <dispatcher>REQUEST</dispatcher>
    <dispatcher>FORWARD</dispatcher>
    <dispatcher>INCLUDE</dispatcher>
</filter-mapping>
            

For deeper integration (including the ability to have a view with combined use of the Spring Faces Ajax components and Rich Faces Ajax components), configure the RichFacesAjaxHandler on your FlowController:

 
<bean id="flowController" class="org.springframework.webflow.mvc.servlet.FlowController">
    <property name="flowExecutor" ref="flowExecutor" />
    <property name="ajaxHandler">
        <bean class="org.springframework.faces.richfaces.RichFacesAjaxHandler"/>
    </property>
</bean>
            

RichFaces Ajax components can be used in conjunction with the render tag to render partial fragments on an Ajax request. Instead of embedding the ids of the components to be re-rendered directly in the view template (as you traditionally do with Rich Faces), you can bind the reRender attribute of a RichFaces Ajax component to a special flowRenderFragments EL variable. For example, in your view template you can have a fragment that you would potentially like to re-render in response to a particular event:

<h:form id="hotels">
    <a4j:outputPanel id="searchResultsFragment">
        <h:outputText id="noHotelsText" value="No Hotels Found" rendered="#{hotels.rowCount == 0}"/>
        <h:dataTable id="hotels" styleClass="summary" value="#{hotels}" var="hotel" rendered="#{hotels.rowCount > 0}">
            <h:column>
                <f:facet name="header">Name</f:facet>
                #{hotel.name}
            </h:column>
            <h:column>
                <f:facet name="header">Address</f:facet>
                #{hotel.address}
            </h:column>
        </h:dataTable>
    </a4j:outputPanel>
</h:form>
            

then a RichFaces Ajax commandLink to fire the event:

<a4j:commandLink id="nextPageLink" value="More Results" action="next" reRender="#{flowRenderFragments}" />
            

and then in your flow definition a transition to handle the event:

<transition on="next">
    <evaluate expression="searchCriteria.nextPage()" />
    <render fragments="hotels:searchResultsFragment" />
</transition>
            

The Apache MyFaces Trinidad library has been tested with the Spring Web Flow's JSF integration and proven to fit in nicely. Deeper integration to allow the Trinidad components and Spring Faces components to play well together has not yet been attempted, but Trinidad provides a pretty thorough solution on its own when used in conjunction with the Spring Web Flow JSF integration.

NOTE: An AjaxHandler implementation for Trinidad is not currently provided out-of-the-box. In order to fully integrate with Trinidad's PPR functionality, a custom implementation should be provided. An community-provided partial example can be found here: SWF-1160

Typical configuration when using Trinidad with Web Flow is as follows in web.xml (in addition what has already been shown):

<context-param>
    <param-name>javax.faces.STATE_SAVING_METHOD</param-name>
    <param-value>server</param-value>
</context-param>

<context-param>
    <param-name>
        org.apache.myfaces.trinidad.CHANGE_PERSISTENCE
    </param-name>
    <param-value>session</param-value>
</context-param>

<context-param>
    <param-name>
        org.apache.myfaces.trinidad.ENABLE_QUIRKS_MODE
    </param-name>
    <param-value>false</param-value>
</context-param>

<filter>
    <filter-name>Trinidad Filter</filter-name>
    <filter-class>
        org.apache.myfaces.trinidad.webapp.TrinidadFilter
    </filter-class>
</filter>

<filter-mapping>
    <filter-name>Trinidad Filter</filter-name>
    <servlet-name>Spring MVC Dispatcher Servlet</servlet-name>
</filter-mapping>

<servlet>
    <servlet-name>Trinidad Resource Servlet</servlet-name>
    <servlet-class>
        org.apache.myfaces.trinidad.webapp.ResourceServlet
    </servlet-class>
</servlet>

<servlet-mapping>
    <servlet-name>resources</servlet-name>
    <url-pattern>/adf/*</url-pattern>
</servlet-mapping>

            

The only supported mechanism for bridging a portlet request to Web Flow is a FlowHandler. The PortletFlowController used in Web Flow 1.0 is no longer supported.

The flow handler, similar to the servlet flow handler, provides hooks that can:

The AbstractFlowHandler class is an implementation of FlowHandler that provides default implementations for these hooks.

In a portlet environment the targeted flow id can not be inferred from the URL and must be defined explicitly in the handler.

public class ViewFlowHandler extends AbstractFlowHandler {
    public String getFlowId() {
        return "view";
    }
}
			

Spring Portlet MVC provides a rich set of methods to map portlet requests. Complete documentation is available in the Spring Reference Documentation.

The booking-portlet-mvc sample application uses a PortletModeHandlerMapping to map portlet requests. The sample application only supports view mode, but support for other portlet modes is available. Other modes can be added and point to the same flow as view mode, or any other flow.

<bean id="portletModeHandlerMapping" 
      class="org.springframework.web.portlet.handler.PortletModeHandlerMapping">
    <property name="portletModeMap">
        <map>
            <entry key="view">
                <bean class="org.springframework.webflow.samples.booking.ViewFlowHandler" />
            </entry>
        </map>
    </property>
</bean>
			

A FlowHandlerAdapter converts the handler mappings to the flow handlers. The flow executor is required as a constructor argument.

<bean id="flowHandlerAdapter" 
      class="org.springframework.webflow.mvc.portlet.FlowHandlerAdapter">
    <constructor-arg ref="flowExecutor" />
</bean>
			

The Portlet API defined three window states: normal, minimized and maximized. The portlet implementation must decide what to render for each of these window states. Web Flow exposes the string value of the window state under portletWindowState via the request map on the external context.

requestContext.getExternalContext().getRequestMap().get("portletWindowState");
			

externalContext.requestMap.portletWindowState
			

The Portlet API defined three portlet modes: view, edit and help. The portlet implementation must decide what to render for each of these modes. Web Flow exposes the string value of the portlet mode under portletMode via the request map on the external context.

requestContext.getExternalContext().getRequestMap().get("portletMode");
			

externalContext.requestMap.portletMode
			

Prior to version 2.1 of Spring Web Flow, support for JSF Portlets was considered experimental and relied on a Portlet Bridge for JSF implementation. Furthermore JSR-329 (the latest specification in this area), which targets Portlet API 2.0 and JSF 1.2 environments at the time of writing is not yet final causing portlet bridge implementations to also remain incomplete.

A closer comparison of Spring Web Flow and a Portlet Bridge for JSF shows the two have significant overlap. They both drive the JSF lifecycle and they both shield JSF from knowledge about Portlet action and render requests.

Considering all of the above, starting with version 2.2, Spring Web Flow provides support for JSF Portlets using its own internal Portlet integration rather than a Portlet Bridge for JSF. We believe this will provide value for Web Flow users by reducing the number of dependencies in what is already a fairly complex combination of technologies with specifications lagging behind.

What this practically means is the configuration required for JSF Portlets is very similar to what is alread documented in the rest of this chapter with the exception of Section 14.4, “Portlet Views”, which is not necessary with JSF.

Review the swf-booking-portlet-faces sample in the Web Flow distribution for a working JSF Portlets example with complete configuration details. The main thing you'll need to notice in addition to what has already been described in this chapter is the faces-config.xml configuration:

<?xml version="1.0"?>
<!DOCTYPE faces-config PUBLIC
  "-//Sun Microsystems, Inc.//DTD JavaServer Faces Config 1.0//EN"
  "http://java.sun.com/dtd/web-facesconfig_1_0.dtd">

<faces-config>
    <application>
        <view-handler>
            org.springframework.faces.webflow.application.portlet.PortletFaceletViewHandler
        </view-handler>  
    </application>
</faces-config>

The Portlet API only allows redirects to be requested from an action request. Because views are rendered on the render request, views and view-states cannot trigger a redirect.

The externalRedirect: view prefix is a convenience for Servlet based flows. An IllegalStateException is thrown if a redirect is requested from a render request.

end-state redirects can be achieved by implementing FlowHandler.handleExecutionOutcome. This callback provides the ActionResponse object which supports redirects.

The portlet container passes the execution key from the previous flow when switching to a new mode. Even if the mode is mapped to a different FlowHandler the flow execution will resume the previous execution. You may switch the mode programatically in your FlowHandler after ending a flow in an ActionRequest.

One way to start a new flow is to create a URL targeting the mode without the execution key.