This document summarizes the Grails webflow plugin, which allows managing page flows and state in Grails applications. It demonstrates a sample webflow for creating a project, and discusses key concepts like flow states, subflows, scopes, and Ajax integration. Tips are provided for testing flows, generating views, and handling breadcrumbs. Potential pitfalls and alternatives to webflows are also outlined. The extended validation plugin is briefly introduced as a way to validate non-domain objects in Grails.

1. Grails webflow
Ivo Houbrechts
Ixor

2. About Ixor
• Since 2002
• 40 experienced ICT professionals
• Software development for the JVM
• Consultancy and product development
• Loyal customers in Finance, Telecom and Government
• www.ixor.be

3. Agenda
• Grails webflow plugin
• Demo app
• Spring webflow framework
• Flow states
• Subflows
• Scopes
• Ajax
• Testing
• Tips & pitfalls
• Alternatives
• Extended validation plugin
• Questions

4. Demo app
• Simple domain model:
• Project
• Developer
• UserStory
• Wizard for creating a project

5. Spring webflow framework
• Manage page flows
• Wizards
• Manage objects
• Scopes
• Manage states
• Back-button hell
• Grails webflow plugin
• Subset of features

6. Defining a grails webflow
def newProjectWizardCleanedUpFlow = {
onStart doOnStart
projectInfo {
on("next", doBindProjectInfo).to("lead")
}
lead {
subflow(controller: "developer", action: "getDeveloper",
input: [experience: Experience.SENIOR])
on("selected", doSetLead).to(selectLeadOrTeam)
on("cancel", doFlashLeadMandatoryMessage).to("lead")
}
team {
on("add").to("addTeamMember")
on("remove", doRemoveTeamMember).to("team")
on("next").to("stories")
}
addTeamMember {
subflow(controller: "developer", action: "getDeveloper”)
…

7. Flow states
• View states
• Action states
• Start and end states
• Subflow states

8. View state: definition
• Renders a view
• Definition:
projectInfo {
on("next").to("lead")
}
• Default view
/controllerName/flowName/viewstateId
• Override with
render(view: "myview")

9. View state: events
• Triggered by user
• Link
<g:link action="newProjectWizard” event="remove">Remove</g:link>
• Button
<g:form action="newProjectWizard">
<g:submitButton name="add" value="Add developer"/>
</g:form>
• Transition
team {
on("add").to("addTeamMember")
on("remove").to("team")
}

10. View state: transition actions
• Used for binding and validation
on("next") {
flow.projectInstance.properties = params
if (!flow.projectInstance.validate(["name", "description"])) {
error()
}
}.to("lead")
• Supports command objects
• Dynamic transitions
on("selected“).to {
if (!flow.projectInstance.validate(["lead"])) {
return "lead"
} else {
return "team"
}
}

11. Action state: definition
saveProject {
action {
if (flow.projectInstance.save()) {
end()
} else {
projectInfo()
}
}
on("end").to("end")
on("projectInfo").to("projectInfo")
}

12. Action state: events
• Events
• Explicit
• call missing method
• Implicit
• success
• exception
saveProject {
action {
def project= projectService.save(flow.projectInstance)
return [project: project]
}
on("success").to("end")
on("ValidationException").to("retry")
on("Exception").to("fatalError")
}

13. Action state: returning a model
saveProject {
action {
def project= projectService.save(flow.projectInstance)
return [project: project]
}
on("success").to("end")
on("ValidationException").to("retry")
on("Exception").to("fatalError")
}
• Merged into flow scope
• Used in next state or view

14. Start and end states
• Start state: first state in flow definition
• End state
• Empty
cancel()
• Redirect
end {
redirect(action: "show", id: flow.projectInstance.id)
}

15. Subflow states
• Like method calls
• Reusable (parts of) flows
• Definition
lead {
subflow(controller: "developer", action: "getDeveloper",
input: [experience: Experience.SENIOR])
on("selected“).to("team")
on("cancel").to("lead")
}
• Events
• Last state of subflow

16. Subflow input (grails 1.4.0)
• Declare input arguments
• Like method arguments (contract)
def getDeveloperFlow = {
input {
experience()
title(required: true)
}
…
• Provide values in subflow call
subflow(controller: "developer", action: "getDeveloper",
input: [experience: Experience.SENIOR, title: "Select lead"])

17. Subflow input (grails 1.4.0)
• Required arguments
• Exception if not provided
• Not possible to use flow standalone
• Default values
def mySubFlow = {
input {
foo() // optional input with no default value
bazz(required: false, value: someConstantValue)
dynamic { flow.someProperty }
dynamicBis (value: someNamedClosure)
}
…

18. Subflow output (grails 1.4.0)
• Define output in end state
selected {
output {
developer {flow.developer}
}
}…
• Retrieve output in calling flow
on("selected") {
flow.projectInstance.lead = currentEvent.attributes.developer
}.to(…)

19. Subflow input and output values
• Constant values
• Defined at flow definition time (application startup)
• Refer to (controller) variables or literal expressions
• Dynamic values
• Evaluated at flow execution time
• Defined with closures
• Applicable in:
• Default input values
• Input values in subflow call
• Output values

20. Scopes
• Standard scopes
• Webflow scopes
• flow
• flow execution, only visible in one flow
• serialized
• conversation
• flow execution, visible for all flows and subflows
• Cf. class members ↔ method arguments (subflow input)
• serialized
• flash
• semantics like grails flash, but different instance
• merged with request scope → omit ‘flash.’ prefix

21. Ajax
• Define transition to current state
• Render template in transition action
stories {
on("remove") {
…
render(template: "newProjectWizard/editStories",
model: [projectInstance: flow.projectInstance])
}.to("stories")
…
• Use remoteLink or formRemote
<g:remoteLink update="editStories" controller="project“
action="newProjectWizard" event="remove"
params="${[name: userStory.name,
ajaxSource: true, execution: params.execution]}">
Remove</g:remoteLink>

22. Testing
• Integration test flows
class ProjectControllerTests extends WebFlowTestCase {
@Override Object getFlow() {
return controller.newProjectWizardFlow
}
protected void setUp() {
//register all subflows
registerFlow("developer/getDeveloper",
new DeveloperController().getDeveloperFlow)
}
void testHappyFlow() {
startFlow()
assert "projectInfo" == flowExecution.activeSession.state.id
controller.params.name = "project name“
signalEvent("next")
assert "x" == flowScope.projectInstance.lead.name
…

23. Tip 1
• Returning flow output to other controller actions
• Use standard grails flash scope
RequestContextHolder.currentRequestAttributes().flashScope.message =
"Project was successfully created"

24. Tip 2
• Create clean readable flow definitions
• Use closure variables
def newProjectWizardCleanedUpFlow = {
onStart doOnStart
projectInfo {
on("next", doBindProjectInfo).to("lead")
}
…
• Define private closures
private def doBindProjectInfo = {
…
}

25. Tip 3
• Flow diagrams (intellij)
• Demo app: grails generate-xml-flow-definitions

26. Tip 4
• Kick start flow views
• grails generate-views
• Change
• action attribute in forms and links
• explicitly fill in the controller attribute in forms and links when
using subflows
• add an event attribute to links
• remove the flash prefix in flash.message
• use submitButton in stead of actionSubmit

27. Tip 5
• Bread crumbs
• <flow:breadCrumbs/>
• Tag source code: see demo app

28. Pitfalls
• Implement java.io.Serializable
• Objects in flow and conversation scope
• Events don’t get fired
• Missing methods are not missing (f.e. scaffold actions)
• Limited execution history
• Back navigation
• Ajax calls increase state count
• Last state is subflow state
• Back navigation after flow completes redirects to subflow

29. Alternatives
• Ad hoc flows
• Where to store state?
• What if user quits in the middle and starts again?
• One-page wizards with ajax
• One page
• One controller action for each step
• Where to store state?
• Subflows with overlays

30. Extended validation plugin
• Validation for non-grails domain classes
• Particularly useful in combination with webflow
• Cascade constraint
static constraints = {
customer(cascade: true)
…
• Instance constraint
static constraints = {
creditCheck(validator: {order ->
if (order.customer.creditScore == CreditScore.BAD
&& order.orderLines.size() > 1) {
return "order.creditCheck.BAD"
}
})
…

31. Extended validation plugin
• Constraint groups
static constraints = {
invoiceData {
customer(cascade: true)
contactPerson(nullable: false, blank: false)
}
…
• Partial validation
order.validate(groups: ["invoiceData"])
order.validate(
includes: ["orderLines"],
excludes: ["orderLines.deliveryAddress"])
• getAllErrorsRecursive() dynamic method

32. Livesnippets
• groovy & grails related documentation
• Demo application
• Code snippets
• Directly linked to demo code
• Github:
https://github.com/houbie/livesnippets
• Cloudfoundry:
http://livesnippets.cloudfoundry.com

33. Questions
?