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Spring Web Flow

Spring Web Flow. Introduction. Spring Web Flow is a subproject of the popular Spring Framework. http://www.springframework.org/webflow. Introduction.

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Spring Web Flow

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  1. Spring Web Flow

  2. Introduction • Spring Web Flow is a subproject of the popular Spring Framework http://www.springframework.org/webflow

  3. Introduction • Spring Web Flow allows to build high-level, reusable, self-contained controller modules called flows that are runnable in any environment

  4. Flows • A flow defines a user dialog that responds to user events to drive the execution of application code to complete a business goal • Flows are defined declaratively using a rich domain-specific language, like XML (XSD)

  5. Spring Web Flowmotivation

  6. Motivation [part1 - flow definition] • Traditionally, defining the UI flow in a web application has been a less than intuitive process • Frameworks like Spring Web MVC force to cut the UI flow into individual controllers and views • Disadvantage: the overall UI flow is not at all clear from looking at the controller definitions

  7. Motivation [part1 - flow definition] • The Spring Web MVC offers a slightly higher level of functionality - form controllers that implement a predefined work flow: • SimpleFormController • AbstractWizardFormController • However, these are still hard coded examples of a more general work flow concept Spring Web Flow

  8. Spring Web Flow solution • Allows to represent the UI flow in a web application in a clear and simple way • The UI flow is clearly visible by looking at the web flow definition (XML file) • Web Flows can be designed to be self-contained modular design and reuse • Consistent web flow definition technique  you're not forced into using specialized controllers for very particular situations

  9. Motivation [part2 - navigation] • Typical web application have a mix of navigation requirements • Free navigations • Controlled flows • Each case bring their own design challenges

  10. Free navigation • A set of pages connected by links • Accessing a link renders a public resource • Examples • Kursa lekciju saraksts: • http://www.webkursi.lv/java-eim/de/index_lectures_lu.html • Otrais praktiskais darbs: • http://www.webkursi.lv/java-eim/de/lab_mvc_portal.html • Users can access resources directly • Can bookmark or send to a friend

  11. Controlled flows • A user task that spans more than one request • The task is the public resource • Examples • Registration • E-shop ordering • Accessing the task URL starts a new “task execution” • Local to the current user’s session • Intermediate steps of an execution are not bookmarked

  12. Effect on design • Free navigation • Stateless • When invoked: • Does work • Selects a view to render • All in one request • A controlled flow is more complex • Stateful • Guides the user through a task with a linear progression • Renders a view to solicit task input as required

  13. Motivation [part3 - scopes] • Three different Servlet scopes that dictate the visibility and location of objects and attributes that are associated with request processing: • Request • Session • Application

  14. Request scope • Has the smallest lifetime • Is unique to each request from a browser • Will be discarded when the view is returned to the browser • Typically contains data sent from the browser • browser headings • request parameters

  15. Session scope • Starts as soon as each unique browser accesses the server • Ends if the server hasn’t received a request within a specified timeout or if explicitly destroyed • This scope allows objects to live across requests • Typically contains e.g. information about the current user • user details • authentication

  16. Application scope • Lives for the duration of the web application deployment • Contains shared application components and configuration elements

  17. The problem with scopes • Many use cases do not fit into the Servlet scopes • Use case span more than one page but do not require the longevity of the session • The Servlet specification is missing the concept of a conversational scope to support the execution of use cases that span multiple pages

  18. Use cases and scopes

  19. Session scope? Why not store everything in the session and manually perform cleanups when the conversation ends? • Server affinity • Greatly increased memory footprint per user • Name space clashes • No vocabulary for process modelling

  20. Spring solution • Spring Web Flow treats conversational scope as a first-level citizen • The core artefact within Spring Web Flow is the flow (or conversation) • Conversations can execute in parallel without intruding on each other • When the conversation has finished, all allocated resources are automatically cleaned up

  21. Spring Web Flow characteristics

  22. Spring Web Flow characteristics • Implementation agnostic • Abstracted away from the Servlet specification • Nothing web-specific about a flow definition • Developer is not presented with an HttpServletRequest or an HttpServletResponse

  23. Spring best practices • Develop against interfaces  plug in the most appropriate implementation • Favor integration with established technologies • Allow reusability from within other established web frameworks • Integrates with Struts, JSF and Portlet MVC • Facilitate test-driven development

  24. Spring Web Flow characteristics • Low adoption overhead • SWF is self-contained  little impact when introducing it on existing projects • Spring Web Flow is another Controller tool in the MVC toolbox • A major design goal of Spring Web Flow was to do one thing and do it well

  25. Spring Web Flowarchitectural overview

  26. Integration options • Spring Web Flow is very self-contained  the entry points to other frameworks are consistent

  27. Inside the SWF System • A central FlowExecutionManager façade is responsible for launching executions of flows on behalf of clients • Flow executions = new user conversations with the server • Each conversation is given its own local data structure, called flow scope

  28. Where is flow scope stored? • Flow scope is stored in a repository • A number of repository implementations to support different usage scenarios: • SimpleFlowExecutionRepository • ContinuationFlowExecutionRepository • ClientContinuationFlowExecutionRepository http://en.wikipedia.org/wiki/Continuation

  29. Building Blocks • With Spring Web Flow, the primary challenge for developers is the design and implementation of aflow definition • Web flow is composed of a set of states • Each state has one or more transitions that are used to move to another state • A transition is triggered by an event

  30. Flows • A flow defines a conversation, or dialogue, between users and theserver

  31. States The steps of a flow are called states. Fivecore types of states: • Action state • Executes application code, typically delegating to a business service in themiddle tier • View state • Renders a view allowing the user to participate in the flow by entering data orviewing a message

  32. States • Subflow state • Spawns another flow as a subflow • Decision state • Evaluates a condition to drive a transition to a new state • End state • Terminates a flow

  33. Transitions • All states (except end states) are transtionable and maintain a set of one or more transitions thatdefine “allowed paths” to other states • A transition is triggered on the occurrence of an event

  34. Events • Nothing more than “something that happens” within a state • An event is treated as a state outcome that captures the logical result of a state’s execution • From the previous slide: • The “submit” event communicates that a submit button was pressed as the outcome of a view state • The “yes” event communicates that a “true” result was returned when evaluating a condition as the outcome of a decision state

  35. Deterministic finite automata http://www.u.arizona.edu/~miller/webthesis/mthesis/node8.html

  36. Sample Application

  37. Sample Application - Phonebook • Allows to locate an employee of the company using some search criteria • Once the right person is found, it is possible to consult detailed information (phone, colleagues) http://www.ervacon.com/products/swf/intro/index.html

  38. Sources and deployed sample Sources: \spring-webflow-1.0.5\projects\spring-webflow-samples\phonebook Deployed sample: http://spring.ervacon.com/swf-phonebook/

  39. Phonebook domain objects • Person - A simple JavaBean containing person details • SearchCriteria - A query object representing a search in the phonebook • SearchCriteriaValidator - A validator to validate a SearchCriteria object • Phonebook - Main business facade interface • public List<Person> search(SearchCriteriacriteria); • public Person getPerson(Long id); • The StubPhonebook implementation of the Phonebook interface just hard-codes some dummy data

  40. Spring Web MVC Setup Need to configure /WEB-INF/web.xml • ContextLoaderListener - initializes the Spring Framework when web application is loaded by the servlet engine • DispatcherServlet - handles all requests matching the URL pattern *.htm

  41. ContextLoaderListener <context-param> <param-name>contextConfigLocation</param-name> <param-value> classpath:org/springframework/webflow/samples/phonebook/stub/services-config.xml </param-value> </context-param> <listener> <listener-class> org.springframework.web.context.ContextLoaderListener </listener-class> </listener> The root application context will be loaded from the services-config.xml classpath resource

  42. services-config.xml <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd"> <bean id="phonebook" class="org.springframework.webflow. samples.phonebook.stub.StubPhonebook"/> </beans> The root web application context, defined in services-config.xml configures business facade: the phonebook bean

  43. DispatcherServlet <servlet> <servlet-name>phonebook</servlet-name> <servlet-class> org.springframework.web.servlet.DispatcherServlet </servlet-class> <init-param> <param-name>contextConfigLocation</param-name> <param-value> /WEB-INF/phonebook-servlet-config.xml /WEB-INF/phonebook-webflow-config.xml </param-value> </init-param> </servlet> <servlet-mapping> <servlet-name>phonebook</servlet-name> <url-pattern>*.htm</url-pattern> </servlet-mapping>

  44. ViewResolver <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans-2.0.xsd"> <bean id="viewResolver" class="org.springframework.web.servlet. view.InternalResourceViewResolver"> <property name="prefix" value="/WEB-INF/jsp/"/> <property name="suffix" value=".jsp"/> </bean> </beans>

  45. Spring Web MVC is configured! Next let’s integrate Spring Web Flow!

  46. The Web Flow Controller • The component that does integration is: org.springframework.webflow.executor.mvc.FlowController • This controller will handle all things Web Flow on behalf of the application • Configure in phonebook-servlet-config.xml: <bean name="/phonebook.htm" class= "org.springframework.webflow.executor.mvc.FlowController"> <property name="flowExecutor" ref="flowExecutor"/> </bean>

  47. Flow executor • All flow execution management responsibilities will be delegated to flow executor • phonebook-webflow-config.xml: <?xml version="1.0" encoding="UTF-8"?> <beans ... > <flow:executor id="flowExecutor" registry-ref="flowRegistry"/> <flow:registry id="flowRegistry"> <flow:location path="/WEB-INF/flows/**-flow.xml"/> </flow:registry> </beans>

  48. Flow registry • The flow registry will load flows from XML files found in the /WEB-INF/flows/ directory that have the -flow.xml suffix • The search flow defined in search-flow.xml will be assigned the id search-flow • The detail flow defined in detail-flow.xml will receive the id detail-flow

  49. Request parameters • Web Flow controller is invoked by the dispatcher servlet to handle a request • It examines the following request parameters to determine what to do: • _flowId • _flowExecutionKey • _eventId

  50. _flowId • Id of a flow for which a new execution should be launched • Possible values in a sample application are • search-flowand detail-flow • If "_flowExecutionKey" parameter is not present, the flow controller launches a new flow execution • The new execution will be assigned a unique key <a href="phonebook.htm?_flowId=search-flow">Phonebook</a>

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