Spring Web Flow

Spring Web Flow
A little flow of happiness.
Presented by – Vikrant

Agenda
 Why Web – Flow ?
 Spring Web-Flow (Basic Introduction)
 Spring Web-Flow Grails Plugin
 Demo

Introduction
Spring Web Flow builds on Spring MVC and allows
implementing the "flows" of a web application. A flow
encapsulates a sequence of steps that guide a user through the
execution of some business task. It spans multiple HTTP
requests, has state, deals with transactional data, is reusable.
Stateful web applications with controlled navigation such as checking
in for a flight, applying for a loan, shopping cart checkout and many
more.
These scenarios have in common is one or more of the following traits:
● There is a clear start and an end point.
● The user must go through a set of screens in a specific order.
● The changes are not finalized until the last step.
● Once complete it shouldn't be possible to repeat a transaction accidentally

Disadvantages of MVC
 Visualizing the flow is very difficult
 Mixed navigation and view
 Overall navigation rules complexity
 All-in-one navigation storage
 Lack of state control/navigation customization

Basic Components
● Flow – A flow defined as a complete life-span of all States transitions.
● States - Within a flow stuff happens. Either the application performs some logic, the
user answers a question or fills out a form, or a decision is made to determine the next
step to take. The points in the flow where these things happen are known as states.
Five different kinds of state: View, Active, Decision, Subflow, and End.
● Transitions - A view state, action state, or subflow state may have any number of
transitions that direct them to other states.
● Flow Data - As a flow progresses, data is either collected, created, or otherwise
manipulated. Depending on the scope of the data, it may be carried around for periods of
time to be processed or evaluated within the flow
● Events – Events are responsible for transition in between states.

Types of State
View States : A view state displays information to a user or obtains user input
using a form. (e.g. JSP.,jsf, gsp etc)
Action States : Action states are where actions are perfomed by the spring beans.
The action state transitions to another state. The action states generally have an
evaluate property that describes what needs to be done.
Decision States: A decision state has two transitions depending on whether the
decision evaluates to true or false.
Subflow States :It may be advantageous to call another flow from one flow to
complete some steps. Passing inputs and expecting outputs.
End States : The end state signifies the end of flow. If the end state is part of a root
flow then the execution is ended. However, if its part of a sub flow then the root flow
is resumed.
Note : Once a flow has ended it can only be resumed from the start state, in this case
showCart, and not from any other state.

Grails Flow Scopes
Grails flows have five different scopes you can utilize:
● request - Stores an object for the scope of the current request
● flash - Stores the object for the current and next request only
● flow - Stores objects for the scope of the flow, removing them when the flow
reaches an end state
● conversation - Stores objects for the scope of the conversation including the
root flow and nested subflows
● session - Stores objects in the user's session

Exception Handling
● Transition on exception
on(Exception).to('error')
● Custom exception handler
on(MyCustomException).to('error')

Dependencies for Spring/Grails
Spring Maven/Gradle Dependencies
Maven POM
<dependencies>
<dependency>
<groupId>org.springframework.webflow</groupId>
<artifactId>spring-webflow</artifactId>
<version>2.4.4.RELEASE</version>
</dependency>
</dependencies>
Gradle
dependencies {
compile 'org.springframework.webflow:spring-webflow:2.4.4.RELEASE'
}
Grails Plugin Installation
plugins{
....
compile ":webflow:2.1.0"
.....
}

Grails Web Flow Plugin
How to define a flow...
class BookController {
def shoppingCartFlow ={ // add flow to action in Controller
state {
}
…
state {
}
...
}
}
Here, Shopping Cart will be considered as a action and will work like a flow.
Note - Views are stored within a directory that matches the name of the flow:
grails-app/views/book/shoppingCart.
URL - localhost:8080/applicationName/book/shoppingCart

How to define a state...
def shoppingCartFlow ={
showCart {
on("checkout").to "enterPersonalDetails"
on("continueShopping").to "displayCatalogue"
}
…
displayCatalogue {
redirect(controller: "catalogue", action: "show")
}
displayInvoice()
}
Here, “showCart” and “displayCatelog” will be considered as a state
URL - localhost:8080/applicationName/book/shoppingCart?execution=e3s14

Action State ...
enterPersonalDetails {
on("submit") {
def p = new Person(params)
flow.person = p
if (!p.validate()) return error()
}.to "enterShipping"
on("return").to "showCart"
}
Here, action{....} state used to perform some action when it enters into the
ShippingNeeded State
enterPersonalDetails {
action { //action State defined and used to
perform stuffs
}
on("submit") .to "enterShipping"
on("return").to "showCart"
}

Decision State ...
shippingNeeded {
action { //action State defined and used to perform stuffs
if (params.shippingRequired) yes()
else no()
}
on("yes").to "enterShipping"
on("no").to "enterPayment"
}
Here, action{....} state used to perform some action when it enters into the
ShippingNeeded State

Sub-Flow State ...
def extendedSearchFlow = {
startExtendedSearch {
on("findMore").to "searchMore"
on("searchAgain").to "noResults"
}
searchMore {
Action {
.........
........
}
on("success").to "moreResults"
on("error").to "noResults"
}
moreResults()
noResults()
}
Here, extendedSearchFlow state used as sub-state
extendedSearch {
// Extended search subflow
subflow(controller: "searchExtensions",
action: "extendedSearch")
on("moreResults").to
"displayMoreResults"
on("noResults").to
"displayNoMoreResults"
}
displayMoreResults()
displayNoMoreResults()

Transition ...
def shoppingCartFlow ={
showCart {
on("checkout").to "enterPersonalDetails" // Transition from one flow to another
on("continueShopping").to "displayCatalogue"
}
…
displayCatalogue {
redirect(controller: "catalogue", action: "show")
}
displayInvoice()
}
Here, On().to() used to transition from one state to another defined in sequence.

Take a special care...
● Once a flow has ended it can only be resumed from the start state
● Throughout the flow life-cycle each html/grails control name should be unique.
● Maintain JSessionId is maintained throughout the flow execution.
● Spring Security is checked only before entering into a flow not in between the states
of executing flow
● When placing objects in flash, flow or conversation scope they must implement
java.io.Serializable or an exception will be thrown
● built-in error() and success() methods.
● Any Exception class in-heirarchy or CustomException Handler Class used to handle
Exceptions

References
1. https://dzone.com/refcardz/spring-web-flow
2. http://projects.spring.io/spring-webflow/
3. https://grails-plugins.github.io/grails-webflow-plugin/guide/
4. https://grails.org/plugin/webflow

Take a look aside practically
Demo !!

Spring Web Flow

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