10. System Setup

10. System Setup
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10.1. Introduction

This chapter shows you how to setup the Web Flow system for use in any web environment.

10.2. webflow-config.xsd

Web Flow provides a Spring schema that allows you to configure the system. To use this schema, include it in one of your infrastructure-layer beans files:

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:webflow="http://www.springframework.org/schema/webflow-config"
       xsi:schemaLocation="
           http://www.springframework.org/schema/beans
           http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
           http://www.springframework.org/schema/webflow-config
           http://www.springframework.org/schema/webflow-config/spring-webflow-config-2.3.xsd">		

    <!-- Setup Web Flow here -->
	
</beans>

10.3. Basic system configuration

The next section shows the minimal configuration required to set up the Web Flow system in your application.

10.3.1. FlowRegistry

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

10.3.2. FlowExecutor

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.

10.4. flow-registry options

This section explores flow-registry configuration options.

10.4.1. Specifying flow locations

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" />

10.4.2. Assigning custom flow identifiers

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

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

10.4.3. Assigning flow meta-attributes

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>

10.4.4. Registering flows using a location pattern

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" />

10.4.5. Flow location base path

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.

10.4.6. Configuring FlowRegistry hierarchies

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>

10.4.7. Configuring custom FlowBuilder services

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="..." />

conversion-service

Use the conversion-service attribute to customize the ConversionService used by the Web Flow system. Type conversion is used to convert from one type to another when required during flow execution such as when processing request parameters, invoking actions, and so on. Many common object types such as numbers, classes, and enums are supported. However you'll probably need to provide your own type conversion and formatting logic for custom data types. Please read Section 5.7, “Performing type conversion” for important information on how to provide custom type conversion logic.

expression-parser

Use the expression-parser attribute to customize the ExpressionParser used by the Web Flow system. The default ExpressionParser uses the Unified EL if available on the classpath, otherwise OGNL is used.

view-factory-creator

Use the view-factory-creator attribute to customize the ViewFactoryCreator used by the Web Flow system. The default ViewFactoryCreator produces Spring MVC ViewFactories capable of rendering JSP, Velocity, and Freemarker views.

The configurable settings are development. These settings are global configuration attributes that can be applied during the flow construction process.

development

Set this to true to switch on flow development mode. Development mode switches on hot-reloading of flow definition changes, including changes to dependent flow resources such as message bundles.

10.5. flow-executor options

This section explores flow-executor configuration options.

10.5.1. Attaching flow execution listeners

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"/>

10.5.2. Tuning FlowExecution persistence

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.

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