Have you begin as your web appliance gets added complex, compassionate and managing the folio breeze – the chart that drives your appliance use cases – gets harder and harder? Are you annoyed of actuality affected into absolute accurate means of accomplishing things that don’t accord you abundant reuse? Do you feel you’re spending too abundant time developing your own approaches to all-encompassing problems like affair accompaniment management?
Enter Spring Web Flow.
Spring Web Breeze (SWF) is an arising bore of The Spring Framework. The bore is allotment of Spring’s web appliance development stack, which includes Spring MVC.
Spring Web Breeze aims to be the best band-aid for the administration of web appliance folio flow. It is a able ambassador for use aback your applications appeal circuitous controlled navigations, such as wizards, to adviser the user through a alternation of accomplish aural a beyond appliance transaction.
An archetype of such a controlled aeronautics is illustrated as a UML Accompaniment Diagram below:
Figure 1 – An Archetype Flight Booking Flow
Astute readers will admit this as a archetypal flight booking breeze – the affectionate you participate every time you book an airline catch on-line.
In acceptable web applications, folio flows like the one aloft are not explicit—they are not aboriginal chic citizens. Booty a webapp congenital on Struts, for example. To apparatus a folio breeze in Struts, best developers body on what the framework provides them: accomplishments and views. In this case, a distinct activity is associated with a specific appeal URL. Aback a appeal comes in at that URL, the activity is executed. During execution, the activity performs some processing and again selects an adapted aftereffect appearance for display. It’s that simple.
So to apparatus a multi-step folio breeze in Struts, alone accomplishments are chained calm through the assorted views. Activity URLs to activity altered contest like “back” or “submit” are hard-coded into anniversary view. Some anatomy of ad-hoc affair accumulator is acclimated to administer breeze state. Redirect afterwards column is acclimated to anticipate alike submissions, etc.
Although this is a simple and anatomic approach, it has a aloft disadvantage: the all-embracing folio breeze of the web appliance is not bright from attractive at the activity definitions in the struts-config.xml file. You can’t see the backwoods – the breeze – from the copse – the abounding activity and appearance definitions. Flexibility additionally suffers aback accomplishments and angle cannot be calmly reused. Finally, you artlessly accept to do too abundant work—it should be easier!
Spring MVC offers a hardly college akin of functionality: anatomy controllers that apparatus a predefined folio flow. Two such controllers are provided out of the box: SimpleFormController and AbstractWizardFormController. However, these are still specific examples of a added accepted folio breeze concept.
Tapestry and JSF use an event-driven access at the folio level, rather than the appeal level, area anniversary folio and its abetment ambassador argumentation are kept together. However, neither provides capital abutment for a analytic folio breeze with a categorical lifecycle that spans several pages and potentially altered paths. As you’ll see, the lifecycle of such a folio breeze is best than a distinct request, but beneath than a session.
This is area Spring Web Breeze comes in, acceptance you to represent the folio breeze of a web appliance in a bright and simple way, and reclaim it anywhere, including environments like Struts, Spring MVC, Tapestry, JSF, and alike Portlets.
As you will see, Spring Web Breeze offers several advantages:
For now it suffices to say that a web breeze is composed of a set of states. A accompaniment is a point in the breeze area commodity happens; for instance, announcement a appearance or alive an action. Anniversary accompaniment has one or added transitions that are acclimated to move to addition state.
A alteration is triggered by an accident .
To authenticate what a web breeze analogue looks like, the afterward allotment of XML captures the flight booking activity illustrated in the UML accompaniment diagram above:
Figure 2 – A XML-based Flight Booking Breeze definition
As you can see, aloof from scanning the XML definition, the analytic breeze alive the booking activity is acutely discernable, alike if you don’t yet apperceive about Spring Web Breeze accomplishing details.
And if you attending a bit closer, you’ll see two subflows that spawn adolescent processes of the booking flow. The aboriginal subflow guides the user through entering his commuter information. The additional has the user accomplish his bench assignments. The adeptness to backup flows that act as “mini appliance modules” is one of the best able capabilities of Spring Web Flow.
You could appearance the analogue aloft to a business analyst and she’d apparently get it. Better yet, you could architect a beheld diagram from this analogue and present that to a business analyst for review. Accoutrement to do absolutely this are already appearing.
The abutting allotment of this commodity break bottomward the key genitalia of the aloft Book flight definition, and provides acknowledging chat that illustrates how Spring Web Breeze works.
The Breeze Definition
Starting with band 1 of the XML-based breeze definition:
The webflow aspect defines the flow, allegorical its id and start-state. The id is artlessly a altered identifier. The alpha accompaniment is the aboriginal accompaniment to alteration to aback a new breeze affair is activated at runtime.
So for this business case, aback a new bookflight affair is activated, it transitions to the obtainTripInfo state.
The Obtain Cruise Info Activity State
Moving on to the obtainTripInfo accompaniment definition.
Recall that aback states are entered, behavior happens. As you’ll see, there are altered accompaniment types that assassinate altered behaviors. An activity state, like obtainTripInfoabove, executes an activity aback entered. That activity allotment the analytic aftereffect of its execution, and that aftereffect is mapped to a accompaniment transition. It’s that simple.
So for this business case, obtainTripInfo, aback entered, executes the bindAndValidate adjustment on the Activity accomplishing with the bookingActions identifier. This adjustment binds anatomy ascribe from the browser to a Cruise area article and validates it. If that activity is successful, the suggestItineraries accompaniment is entered. If an absurdity occurs, the tryAgain accompaniment is entered.
The Booking Action
When appliance Spring Web Breeze with Spring IoC, the bean aspect of the activity aspect refers to the name of an Activity accomplishing exported in the Spring Appliance Context. Here, the bookingActions bean analogue looks like this:
This allows our activity accomplishing to be managed by Spring and configured via annex injection.
The Suggest Itineraries Activity State
Now booty a attending at the abutting activity accompaniment that, accustomed a apprenticed and accurate Cruise article as input, allotment a accumulating of adapted itineraries:
The absolute accomplishing cipher adapted to accomplish this appear is straightforward:
When the suggestItineraries accompaniment is entered, the suggestItineraries adjustment is invoked. The added activity states assignment in absolutely the aforementioned way: entering the accompaniment invokes a adjustment on the ambition activity bean.
The Affectation Adapted Itineraries Appearance State
Once a accumulating of adapted itineraries is returned, the abutting footfall has the user analysis them so she may baddest the best one. This is able by the afterward accompaniment definition:
As you can see, displaySuggestedItineraries is a appearance state—a accompaniment blazon we accept not yet discussed. A appearance state, aback entered, causes the alive breeze to pause, and allotment ascendancy aback to the applicant with apprenticeship to cede the configured view. Later, afterwards some user think-time, the applicant signals an accident anecdotic what activity the user took. That resumes the flow, and the accident that occurred is mapped to a accompaniment transition, which takes the user to the abutting footfall in the flow. Again, it’s that simple.
So for this business case, aback the displaySuggestedItineraries accompaniment is entered the suggestedIteneraries appearance is rendered and ascendancy allotment to the browser. The user again decides which beat she wants and clicks the “select” button. That signals the baddest event, casual in the id of the called beat as an accident parameter.
The user may additionally accept to startOver, at which time the breeze transitions to the abolish state.
Note it is the albatross of the applicant ambiance the breeze is hosted in to map the requested appearance name, like suggestedItineraries, to a renderable appearance template, like /WEB-INF/jsp/suggestedIternaries.jsp. For example, in Spring MVC, the FlowController does this appliance the accustomed ModelAndView and ViewResolver constructs. In Struts, the FlowAction does this appliance the accustomed ActionForward.
Client Side State
At this point you ability ask:
“… aback the alive breeze is paused aback a ViewState is entered, and ascendancy is alternate to the browser, how is the aforementioned breeze best up and resumed on consecutive events?”
The acknowledgment is the applicant advance the altered id of the alive flow, and provides it as ascribe aback the abutting accident is signaled. This is about done appliance a hidden anatomy field.
For example, in a jsp:
The “Is Commuter Info Required?” Accommodation State
After the user selects the Beat she wants, the breeze has to accomplish a contextual accommodation about area to go next.
Specifically, if the user has not logged in, or she has logged in but wishes to affirm her commuter advice – like the acclaim agenda she will use – the breeze should acquiesce her to access that information. On the added hand, if she has already logged in and wishes to go beeline to the booking page, the breeze should skip this alternative step.
Basically, a activating accommodation has to be fabricated that takes into annual the user’s advice and preferences.
The accommodation accompaniment is absolute for this. See the analogue below:
The Access Commuter Advice SubFlow State
The activity of managing commuter advice is logically absolute of the booking process. It is one allotment aural that process, yes, but it absolutely makes faculty a user would appetite to adapt her advice alfresco of the booking context.
Subflow states facilitate this. Aback a subflow accompaniment is entered, a adolescent breeze is spawned. The ancestor breeze is abeyant until the adolescent breeze ends. This lets you appearance your appliance as a set of absolute modules – flows – that you can calmly bury in assorted situations in a constant manner.
Take a attending at the enterPassengerInformation subflow state:
The breeze aspect is the id of the breeze to spawn aback this accompaniment is entered. The attribute-mapper aspect maps attributes to and from the subflow. Ascribe mappings map attributes bottomward to the subflow. Output mappings map attributes aback up to the ancestor breeze aback the subflow ends. As you can see, expressions (in this case OGNL) are additionally supported.
So for this business case, aback the enterPassengerInformation accompaniment is entered, the commuter breeze is spawned. The passengerId aspect is anesthetized bottomward to the breeze as input. From there, the subflow does whatever it wants. It’s a atramentous box as far the ancestor breeze is concerned. Aback the subflow ends, the ancestor breeze resumes, responding to the catastrophe aftereffect to actuate area to go next—in this case, to catch verification.
The Affectation Acceptance End State
There is one aftermost amount accompaniment blazon that has yet to be discussed: the end state. Aback an end accompaniment is entered, the alive breeze affair terminates. Upon termination, all assets associated with the breeze are bankrupt up for you automatically.
Below is the displayConfirmation end accompaniment that displays acceptance afterwards an beat is auspiciously booked:
When this accompaniment is entered, the bookflight breeze ends and the reservationConfirmation appearance displays. Because the bookflight breeze was acting as the basis flow, and not a subflow, it and any allocated assets are automatically bankrupt up.
Note: had the catastrophe breeze been acting as a subflow, the entered end accompaniment is advised as a subflow aftereffect the resuming ancestor breeze can acknowledge to. Added specifically, the entered end accompaniment ID is acclimated as area for a accompaniment alteration in the resuming ancestor flow’s subflow state. You can see this in activity by demography a attending at the “enterPassengerInformation” subflow accompaniment definition. Note how it responds to the “finish” aftereffect of the subflow, which corresponds to a “finish” end accompaniment aural the commuter flow.
So far you’ve abstruse what Spring Web Breeze is all about, and you’ve apparent an archetype of a astute breeze definition. What you haven’t apparent yet is how to arrange that breeze analogue for beheading in a accurate environment, like Spring MVC in a servlet environment.
Doing this is a cinch. Here’s all you accept to do with Spring MVC:
This automatically exports the bookingFlow at the /booking.htm URL for use in a servlet environment.
The afterward area introduces some of the added avant-garde appearance of Spring Web Flow.
The FlowExecutionListener assemble is an eyewitness that allows you to accept and acknowledge to the lifecycle of an alive flow. You can use this affection to do annihilation from accompaniment arrangement and column action checks, to auditing and security.
The apparatus by which the accompaniment of an alive breeze is adored and adequate is absolutely pluggable. HttpSession-based accumulator is the default, and SWF provides two added accumulator strategies out of the box: one appliance server-side continuation-based affair storage, addition appliance abounding client-side serialization. Defining your own custom storage, for archetype to abundance breeze accompaniment in a Database, is trivial.
It should be acclaimed that Spring Web Breeze is not a one-size-fits-all solution. As you’ve seen, it’s a stateful arrangement that automates the administration of folio flows that drive business processes. It should not be acclimated aback simpler, stateless solutions are added appropriate. For example, it should not be acclimated area sites crave chargeless navigations, area the user is chargeless to “click around” anywhere they please. Spring Web Breeze is advised to ability controlled navigations, area the user is guided through a activity with a bright business ambition and lifecycle.
To added accomplish the use case added concrete, actuality are some examples of “good flows”, area the SWF arrangement would be appropriate:
Here are some examples area Spring Web Breeze would not be appropriate:
Spring Web Breeze is meant to be acclimated as a acclaim to acceptable controllers aural any web environment, such as Spring MVC, Struts, Tapestry, Web Work, JSF, or Portlets. A distinct armpit should amalgamate use of simple controllers with web flows area appropriate.
Spring Web Breeze 1.0 final will be appear with Spring 1.3, appointed appropriate afore JavaOne in June. Between now and then, apprehend regular, stable-for-development-use examination releases. The alms is already absolutely complete in agreement of affection set and sample applications.
As the development aggregation pushes afterpiece to a final release, actuality are some of the best important appearance we will be alive on:
As a standalone library, Spring Web Breeze is a able fit for affiliation with added frameworks. Out of the box Spring MVC, Struts, and Portlet MVC affiliation is already provided. JSF and Tapestry affiliation are accepted by the final release.
With Spring 1.2, exporting beans in an MBeanServer for administration and ecology is easy. A acerb typed FlowExecutionMBean administration interface already exists, and we plan to extend that so all-around statistics on all flows alive on the server can be centrally monitored through a JMX console.
Every assemble in the arrangement will be fabricated pluggable for accessible addendum and customization, alike from the xml definition. This includes States and Transitions, amid added concepts.
Supporting appearance and sample applications demonstrating use of compensating affairs to acknowledgment ahead committed assignment during beheading of a breeze is of aerial absorption to us.
Spring Web Breeze is a able band-aid for managing controlled navigations that drive business processes. And it’s fun to assignment with. If you haven’t approved it already, what are you cat-and-mouse for?
Spring Web Breeze is covered in the Amount Spring training advance offered by Interface21 – http://www.springframework.com/training
The Spring Framework, http://www.springframework.org
The Spring Web Breeze Wiki, http://opensource.atlassian.com/confluence/spring/display/WEBFLOW/Home
The kdonald blog, https://www.jroller.com/page/kdonald
Java Server Faces, http://java.sun.com/j2ee/javaserverfaces/
Keith Donald is an Interface21 arch and a amount Spring Framework activity member. An accomplished developer and mentor, Keith has congenital applications for barter spanning a assorted set of industries including banking, arrangement management, advice assurance, education, and retail. He specializes in advice business requirements into abstruse solutions. Keith is the architect of the Spring Rich Applicant Activity and co-lead of Spring Web Breeze with Erwin Vervaet. Lately you can acquisition him arch Spring Training courses beyond the US and abroad, and as a bedfellow apostle on Spring with the NoFluffJustStuff (NFJS) tour.
Erwin Vervaet is a software architect with a agog absorption in applying avant-garde IT concepts and tools. He has been appliance the Java accent aback 1996, and has a master’s amount in computer science from the Katholieke Universiteit Leuven in Belgium. He has been complex in IT research, e-commerce projects, accessible antecedent initiatives, and automated software systems. Erwin currently works as an absolute consultant.
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