(window.webpackJsonp=window.webpackJsonp||[]).push([[343],{768:function(e,t,a){"use strict";a.r(t);var n=a(56),s=Object(n.a)({},(function(){var e=this,t=e.$createElement,a=e._self._c||t;return a("ContentSlotsDistributor",{attrs:{"slot-key":e.$parent.slotKey}},[a("h1",{attrs:{id:"_3-defining-flows"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-defining-flows"}},[e._v("#")]),e._v(" 3. Defining Flows")]),e._v(" "),a("h2",{attrs:{id:"_3-1-introduction"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-1-introduction"}},[e._v("#")]),e._v(" 3.1. Introduction")]),e._v(" "),a("p",[e._v("This chapter begins the Users Section.\nIt shows how to implement flows using the flow definition language.\nBy the end of this chapter you should have a good understanding of language constructs, and be capable of authoring a flow definition.")]),e._v(" "),a("h2",{attrs:{id:"_3-2-what-is-a-flow"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-2-what-is-a-flow"}},[e._v("#")]),e._v(" 3.2. What is a flow?")]),e._v(" "),a("p",[e._v("A flow encapsulates a reusable sequence of steps that can execute in different contexts.\nBelow is a "),a("a",{attrs:{href:"http://www.jjg.net/ia/visvocab/",target:"_blank",rel:"noopener noreferrer"}},[e._v("Garrett Information Architecture"),a("OutboundLink")],1),e._v(" diagram illustrating a reference to a flow that encapsulates the steps of a hotel booking process:")]),e._v(" "),a("img",{attrs:{src:"images/hotels-site.png",align:"middle"}}),e._v(" "),a("p",[e._v("Site Map illustrating a reference to a flow")]),e._v(" "),a("h2",{attrs:{id:"_3-3-what-is-the-makeup-of-a-typical-flow"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-3-what-is-the-makeup-of-a-typical-flow"}},[e._v("#")]),e._v(" 3.3. What is the makeup of a typical flow?")]),e._v(" "),a("p",[e._v('In Spring Web Flow, a flow consists of a series of steps called "states".\nEntering a state typically results in a view being displayed to the user.\nOn that view, user events occur that are handled by the state.\nThese events can trigger transitions to other states which result in view navigations.')]),e._v(" "),a("p",[e._v("The example below shows the structure of the book hotel flow referenced in the previous diagram:")]),e._v(" "),a("img",{attrs:{src:"images/hotels-site-bookhotel-flow.png",align:"middle"}}),e._v(" "),a("p",[e._v("Flow diagram")]),e._v(" "),a("h2",{attrs:{id:"_3-4-how-are-flows-authored"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-4-how-are-flows-authored"}},[e._v("#")]),e._v(" 3.4. How are flows authored?")]),e._v(" "),a("p",[e._v("Flows are authored by web application developers using a simple XML-based flow definition language.\nThe next steps of this guide will walk you through the elements of this language.")]),e._v(" "),a("h2",{attrs:{id:"_3-5-essential-language-elements"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-5-essential-language-elements"}},[e._v("#")]),e._v(" 3.5. Essential language elements")]),e._v(" "),a("h3",{attrs:{id:"_3-5-1-flow"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-5-1-flow"}},[e._v("#")]),e._v(" 3.5.1. flow")]),e._v(" "),a("p",[e._v("Every flow begins with the following root element:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<?xml version="1.0" encoding="UTF-8"?>\n<flow xmlns="http://www.springframework.org/schema/webflow"\n      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"\n      xsi:schemaLocation="http://www.springframework.org/schema/webflow\n                          http://www.springframework.org/schema/webflow/spring-webflow.xsd">\n\n</flow>\n\t\t\t\n')])])]),a("p",[e._v("All states of the flow are defined within this element.\nThe first state defined becomes the flow's starting point.")]),e._v(" "),a("h3",{attrs:{id:"_3-5-2-view-state"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-5-2-view-state"}},[e._v("#")]),e._v(" 3.5.2. view-state")]),e._v(" "),a("p",[e._v("Use the "),a("code",[e._v("view-state")]),e._v(" element to define a step of the flow that renders a view:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<view-state id="enterBookingDetails" />\n\t\t\t\n')])])]),a("p",[e._v("By convention, a view-state maps its id to a view template in the directory where the flow is located.\nFor example, the state above might render "),a("code",[e._v("/WEB-INF/hotels/booking/enterBookingDetails.xhtml")]),e._v("if the flow itself was located in the "),a("code",[e._v("/WEB-INF/hotels/booking")]),e._v(" directory.")]),e._v(" "),a("h3",{attrs:{id:"_3-5-3-transition"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-5-3-transition"}},[e._v("#")]),e._v(" 3.5.3. transition")]),e._v(" "),a("p",[e._v("Use the "),a("code",[e._v("transition")]),e._v(" element to handle events that occur within a state:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<view-state id="enterBookingDetails">\n    <transition on="submit" to="reviewBooking" />\n</view-state>\n\t\t\t\n')])])]),a("p",[e._v("These transitions drive view navigations.")]),e._v(" "),a("h3",{attrs:{id:"_3-5-4-end-state"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-5-4-end-state"}},[e._v("#")]),e._v(" 3.5.4. end-state")]),e._v(" "),a("p",[e._v("Use the "),a("code",[e._v("end-state")]),e._v(" element to define a flow outcome:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<end-state id="bookingCancelled" />\n\t\t\t\n')])])]),a("p",[e._v("When a flow transitions to a end-state it terminates and the outcome is returned.")]),e._v(" "),a("h3",{attrs:{id:"_3-5-5-checkpoint-essential-language-elements"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-5-5-checkpoint-essential-language-elements"}},[e._v("#")]),e._v(" 3.5.5. Checkpoint: Essential language elements")]),e._v(" "),a("p",[e._v("With the three elements "),a("code",[e._v("view-state")]),e._v(", "),a("code",[e._v("transition")]),e._v(", and "),a("code",[e._v("end-state")]),e._v(", you can quickly express your view navigation logic.\nTeams often do this before adding flow behaviors so they can focus on developing the user interface of the application with end users first.\nBelow is a sample flow that implements its view navigation logic using these elements:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<flow xmlns="http://www.springframework.org/schema/webflow"\n      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"\n      xsi:schemaLocation="http://www.springframework.org/schema/webflow\n                          http://www.springframework.org/schema/webflow/spring-webflow.xsd">\n\n    <view-state id="enterBookingDetails">\n        <transition on="submit" to="reviewBooking" />\n    </view-state>\n\n    <view-state id="reviewBooking">\n        <transition on="confirm" to="bookingConfirmed" />\n        <transition on="revise" to="enterBookingDetails" />\n        <transition on="cancel" to="bookingCancelled" />\n    </view-state>\n\n    <end-state id="bookingConfirmed" />\n\n    <end-state id="bookingCancelled" />\n\n</flow>\n\t\t\t\n')])])]),a("h2",{attrs:{id:"_3-6-actions"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-6-actions"}},[e._v("#")]),e._v(" 3.6. Actions")]),e._v(" "),a("p",[e._v("Most flows need to express more than just view navigation logic.\nTypically they also need to invoke business services of the application or other actions.")]),e._v(" "),a("p",[e._v("Within a flow, there are several points where you can execute actions. These points are:")]),e._v(" "),a("ul",[a("li",[a("p",[e._v("On flow start")])]),e._v(" "),a("li",[a("p",[e._v("On state entry")])]),e._v(" "),a("li",[a("p",[e._v("On view render")])]),e._v(" "),a("li",[a("p",[e._v("On transition execution")])]),e._v(" "),a("li",[a("p",[e._v("On state exit")])]),e._v(" "),a("li",[a("p",[e._v("On flow end")])])]),e._v(" "),a("p",[e._v("Actions are defined using a concise expression language. Spring Web Flow uses the Unified EL by default.\nThe next few sections will cover the essential language elements for defining actions.")]),e._v(" "),a("h3",{attrs:{id:"_3-6-1-evaluate"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-6-1-evaluate"}},[e._v("#")]),e._v(" 3.6.1. evaluate")]),e._v(" "),a("p",[e._v("The action element you will use most often is the "),a("code",[e._v("evaluate")]),e._v(" element.\nUse the "),a("code",[e._v("evaluate")]),e._v(" element to evaluate an expression at a point within your flow.\nWith this single tag you can invoke methods on Spring beans or any other flow variable.\nFor example:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<evaluate expression="entityManager.persist(booking)" />\n\t\t\t\n')])])]),a("h4",{attrs:{id:"assigning-an-evaluate-result"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#assigning-an-evaluate-result"}},[e._v("#")]),e._v(" Assigning an evaluate result")]),e._v(" "),a("p",[e._v("If the expression returns a value, that value can be saved in the flow's data model called "),a("code",[e._v("flowScope")]),e._v(":")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<evaluate expression="bookingService.findHotels(searchCriteria)" result="flowScope.hotels" />\n\t\t\t\t\n')])])]),a("h4",{attrs:{id:"converting-an-evaluate-result"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#converting-an-evaluate-result"}},[e._v("#")]),e._v(" Converting an evaluate result")]),e._v(" "),a("p",[e._v("If the expression returns a value that may need to be converted, specify the desired type using the "),a("code",[e._v("result-type")]),e._v(" attribute:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<evaluate expression="bookingService.findHotels(searchCriteria)" result="flowScope.hotels"\n          result-type="dataModel"/>\n\t\t\t\t\n')])])]),a("h3",{attrs:{id:"_3-6-2-checkpoint-flow-actions"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-6-2-checkpoint-flow-actions"}},[e._v("#")]),e._v(" 3.6.2. Checkpoint: flow actions")]),e._v(" "),a("p",[e._v("Now review the sample booking flow with actions added:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<flow xmlns="http://www.springframework.org/schema/webflow"\n      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"\n      xsi:schemaLocation="http://www.springframework.org/schema/webflow\n                          http://www.springframework.org/schema/webflow/spring-webflow.xsd">\n\n    <input name="hotelId" />\n\n    <on-start>\n        <evaluate expression="bookingService.createBooking(hotelId, currentUser.name)"\n                  result="flowScope.booking" />\n    </on-start>\n\n    <view-state id="enterBookingDetails">\n        <transition on="submit" to="reviewBooking" />\n    </view-state>\n\n    <view-state id="reviewBooking">\n        <transition on="confirm" to="bookingConfirmed" />\n        <transition on="revise" to="enterBookingDetails" />\n        <transition on="cancel" to="bookingCancelled" />\n    </view-state>\n\n    <end-state id="bookingConfirmed" />\n\n    <end-state id="bookingCancelled" />\n\n</flow>\n\t\t\t\n')])])]),a("p",[e._v("This flow now creates a Booking object in flow scope when it starts.\nThe id of the hotel to book is obtained from a flow input attribute.")]),e._v(" "),a("h2",{attrs:{id:"_3-7-input-output-mapping"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-7-input-output-mapping"}},[e._v("#")]),e._v(" 3.7. Input/Output Mapping")]),e._v(" "),a("p",[e._v("Each flow has a well-defined input/output contract.\nFlows can be passed input attributes when they start, and can return output attributes when they end.\nIn this respect, calling a flow is conceptually similar to calling a method with the following signature:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v("FlowOutcome flowId(Map<String, Object> inputAttributes);\n\t\t\n")])])]),a("p",[e._v("... where a "),a("code",[e._v("FlowOutcome")]),e._v(" has the following signature:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v("public interface FlowOutcome {\n   public String getName();\n   public Map<String, Object> getOutputAttributes();\n}\n\t\t\n")])])]),a("h3",{attrs:{id:"_3-7-1-input"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-7-1-input"}},[e._v("#")]),e._v(" 3.7.1. input")]),e._v(" "),a("p",[e._v("Use the "),a("code",[e._v("input")]),e._v(" element to declare a flow input attribute:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<input name="hotelId" />\n\t\t\t\n')])])]),a("p",[e._v("Input values are saved in flow scope under the name of the attribute.\nFor example, the input above would be saved under the name "),a("code",[e._v("hotelId")]),e._v(".")]),e._v(" "),a("h4",{attrs:{id:"declaring-an-input-type"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#declaring-an-input-type"}},[e._v("#")]),e._v(" Declaring an input type")]),e._v(" "),a("p",[e._v("Use the "),a("code",[e._v("type")]),e._v(" attribute to declare the input attribute's type:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<input name="hotelId" type="long" />\n\t\t\t\t\n')])])]),a("p",[e._v("If an input value does not match the declared type, a type conversion will be attempted.")]),e._v(" "),a("h4",{attrs:{id:"assigning-an-input-value"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#assigning-an-input-value"}},[e._v("#")]),e._v(" Assigning an input value")]),e._v(" "),a("p",[e._v("Use the "),a("code",[e._v("value")]),e._v(" attribute to specify an expression to assign the input value to:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<input name="hotelId" value="flowScope.myParameterObject.hotelId" />\n\t\t\t\t\n')])])]),a("p",[e._v("If the expression's value type can be determined, that metadata will be used for type coersion if no "),a("code",[e._v("type")]),e._v(" attribute is specified.")]),e._v(" "),a("h4",{attrs:{id:"marking-an-input-as-required"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#marking-an-input-as-required"}},[e._v("#")]),e._v(" Marking an input as required")]),e._v(" "),a("p",[e._v("Use the "),a("code",[e._v("required")]),e._v(" attribute to enforce the input is not null or empty:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<input name="hotelId" type="long" value="flowScope.hotelId" required="true" />\n\t\t\t\t\n')])])]),a("h3",{attrs:{id:"_3-7-2-output"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-7-2-output"}},[e._v("#")]),e._v(" 3.7.2. output")]),e._v(" "),a("p",[e._v("Use the "),a("code",[e._v("output")]),e._v(" element to declare a flow output attribute.\nOutput attributes are declared within end-states that represent specific flow outcomes.")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<end-state id="bookingConfirmed">\n    <output name="bookingId" />\n</end-state>\n\t\t\t\n')])])]),a("p",[e._v("Output values are obtained from flow scope under the name of the attribute.\nFor example, the output above would be assigned the value of the "),a("code",[e._v("bookingId")]),e._v(" variable.")]),e._v(" "),a("h4",{attrs:{id:"specifying-the-source-of-an-output-value"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#specifying-the-source-of-an-output-value"}},[e._v("#")]),e._v(" Specifying the source of an output value")]),e._v(" "),a("p",[e._v("Use the "),a("code",[e._v("value")]),e._v(" attribute to denote a specific output value expression:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<output name="confirmationNumber" value="booking.confirmationNumber" />\n\t\t\t\t\n')])])]),a("h3",{attrs:{id:"_3-7-3-checkpoint-input-output-mapping"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-7-3-checkpoint-input-output-mapping"}},[e._v("#")]),e._v(" 3.7.3. Checkpoint: input/output mapping")]),e._v(" "),a("p",[e._v("Now review the sample booking flow with input/output mapping:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<flow xmlns="http://www.springframework.org/schema/webflow"\n      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"\n      xsi:schemaLocation="http://www.springframework.org/schema/webflow\n                          http://www.springframework.org/schema/webflow/spring-webflow.xsd">\n\n    <input name="hotelId" />\n\n    <on-start>\n        <evaluate expression="bookingService.createBooking(hotelId, currentUser.name)"\n                  result="flowScope.booking" />\n    </on-start>\n\n    <view-state id="enterBookingDetails">\n        <transition on="submit" to="reviewBooking" />\n    </view-state>\n\n    <view-state id="reviewBooking">\n        <transition on="confirm" to="bookingConfirmed" />\n        <transition on="revise" to="enterBookingDetails" />\n        <transition on="cancel" to="bookingCancelled" />\n    </view-state>\n\n    <end-state id="bookingConfirmed" >\n        <output name="bookingId" value="booking.id"/>\n    </end-state>\n\n    <end-state id="bookingCancelled" />\n\n</flow>\n\t\t\t\n')])])]),a("p",[e._v("The flow now accepts a "),a("code",[e._v("hotelId")]),e._v(" input attribute and returns a "),a("code",[e._v("bookingId")]),e._v(" output attribute\nwhen a new booking is confirmed.")]),e._v(" "),a("h2",{attrs:{id:"_3-8-variables"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-8-variables"}},[e._v("#")]),e._v(" 3.8. Variables")]),e._v(" "),a("p",[e._v("A flow may declare one or more instance variables.\nThese variables are allocated when the flow starts.\nAny "),a("code",[e._v("@Autowired")]),e._v(" transient references the variable holds are also rewired when the flow resumes.")]),e._v(" "),a("h3",{attrs:{id:"_3-8-1-var"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-8-1-var"}},[e._v("#")]),e._v(" 3.8.1. var")]),e._v(" "),a("p",[e._v("Use the "),a("code",[e._v("var")]),e._v(" element to declare a flow variable:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<var name="searchCriteria" class="com.mycompany.myapp.hotels.search.SearchCriteria"/>\n\t\t\t\n')])])]),a("p",[e._v("Make sure your variable's class implements "),a("code",[e._v("java.io.Serializable")]),e._v(", as the instance state is saved between flow requests.")]),e._v(" "),a("h2",{attrs:{id:"_3-9-variable-scopes"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-9-variable-scopes"}},[e._v("#")]),e._v(" 3.9. Variable Scopes")]),e._v(" "),a("p",[e._v("Web Flow can store variables in one of several scopes:")]),e._v(" "),a("h3",{attrs:{id:"_3-9-1-flow-scope"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-9-1-flow-scope"}},[e._v("#")]),e._v(" 3.9.1. Flow Scope")]),e._v(" "),a("p",[e._v("Flow scope gets allocated when a flow starts and destroyed when the flow ends.\nWith the default implementation, any objects stored in flow scope need to be Serializable.")]),e._v(" "),a("h3",{attrs:{id:"_3-9-2-view-scope"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-9-2-view-scope"}},[e._v("#")]),e._v(" 3.9.2. View Scope")]),e._v(" "),a("p",[e._v("View scope gets allocated when a "),a("code",[e._v("view-state")]),e._v(" enters and destroyed when the state exits.\nView scope is "),a("em",[e._v("only")]),e._v(" referenceable from within a "),a("code",[e._v("view-state")]),e._v(". With the\ndefault implementation, any objects stored in view scope need to be Serializable.")]),e._v(" "),a("h3",{attrs:{id:"_3-9-3-request-scope"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-9-3-request-scope"}},[e._v("#")]),e._v(" 3.9.3. Request Scope")]),e._v(" "),a("p",[e._v("Request scope gets allocated when a flow is called and destroyed when the flow returns.")]),e._v(" "),a("h3",{attrs:{id:"_3-9-4-flash-scope"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-9-4-flash-scope"}},[e._v("#")]),e._v(" 3.9.4. Flash Scope")]),e._v(" "),a("p",[e._v("Flash scope gets allocated when a flow starts, cleared after every view render, and destroyed when the\nflow ends. With the default implementation, any objects stored in flash scope need to be Serializable.")]),e._v(" "),a("h3",{attrs:{id:"_3-9-5-conversation-scope"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-9-5-conversation-scope"}},[e._v("#")]),e._v(" 3.9.5. Conversation Scope")]),e._v(" "),a("p",[e._v("Conversation scope gets allocated when a top-level flow starts and destroyed when the top-level flow ends.\nConversation scope is shared by a top-level flow and all of its subflows. With the default\nimplementation, conversation scoped objects are stored in the HTTP session and should generally be\nSerializable to account for typical session replication.")]),e._v(" "),a("p",[e._v("The scope to use is often determined contextually, for example depending on where a\nvariable is defined -- at the start of the flow definition (flow scope), inside a\na view state (view scope), etc. In other cases, for example in EL expressions and\nJava code, it needs to be specified explicitly. Subsequent sections explain\nhow this is done.")]),e._v(" "),a("h2",{attrs:{id:"_3-10-calling-subflows"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-10-calling-subflows"}},[e._v("#")]),e._v(" 3.10. Calling subflows")]),e._v(" "),a("p",[e._v("A flow may call another flow as a subflow. The flow will wait until the subflow returns, then respond to the subflow outcome.")]),e._v(" "),a("h3",{attrs:{id:"_3-10-1-subflow-state"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-10-1-subflow-state"}},[e._v("#")]),e._v(" 3.10.1. subflow-state")]),e._v(" "),a("p",[e._v("Use the "),a("code",[e._v("subflow-state")]),e._v(" element to call another flow as a subflow:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<subflow-state id="addGuest" subflow="createGuest">\n    <transition on="guestCreated" to="reviewBooking">\n        <evaluate expression="booking.guests.add(currentEvent.attributes.guest)" />\n    </transition>\n    <transition on="creationCancelled" to="reviewBooking" />\n</subflow-state>\n\t\t\t\n')])])]),a("p",[e._v("The above example calls the "),a("code",[e._v("createGuest")]),e._v(" flow, then waits for it to return.\nWhen the flow returns with a "),a("code",[e._v("guestCreated")]),e._v(" outcome, the new guest is added to the booking's guest list.")]),e._v(" "),a("h4",{attrs:{id:"passing-a-subflow-input"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#passing-a-subflow-input"}},[e._v("#")]),e._v(" Passing a subflow input")]),e._v(" "),a("p",[e._v("Use the "),a("code",[e._v("input")]),e._v(" element to pass input to the subflow:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<subflow-state id="addGuest" subflow="createGuest">\n    <input name="booking" />\n    <transition to="reviewBooking" />\n</subflow-state>\n\t\t\t\t\n')])])]),a("h4",{attrs:{id:"mapping-subflow-output"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#mapping-subflow-output"}},[e._v("#")]),e._v(" Mapping subflow output")]),e._v(" "),a("p",[e._v("When a subflow completes, its end-state id is returned to the calling flow as\nthe event to use to continue navigation.")]),e._v(" "),a("p",[e._v("The subflow can also create output attributes to which the calling flow can refer\nwithin an outcome transition as follows:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<transition on="guestCreated" to="reviewBooking">\n    <evaluate expression="booking.guests.add(currentEvent.attributes.guest)" />\n</transition>\n\t\t\t\t\n')])])]),a("p",[e._v("In the above example, "),a("code",[e._v("guest")]),e._v(" is the name of an output attribute returned by the "),a("code",[e._v("guestCreated")]),e._v(" outcome.")]),e._v(" "),a("h3",{attrs:{id:"_3-10-2-checkpoint-calling-subflows"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#_3-10-2-checkpoint-calling-subflows"}},[e._v("#")]),e._v(" 3.10.2. Checkpoint: calling subflows")]),e._v(" "),a("p",[e._v("Now review the sample booking flow calling a subflow:")]),e._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[e._v('<flow xmlns="http://www.springframework.org/schema/webflow"\n      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"\n      xsi:schemaLocation="http://www.springframework.org/schema/webflow\n                          http://www.springframework.org/schema/webflow/spring-webflow.xsd">\n\n    <input name="hotelId" />\n\n    <on-start>\n        <evaluate expression="bookingService.createBooking(hotelId, currentUser.name)"\n                  result="flowScope.booking" />\n    </on-start>\n\n    <view-state id="enterBookingDetails">\n        <transition on="submit" to="reviewBooking" />\n    </view-state>\n\n    <view-state id="reviewBooking">\n        <transition on="addGuest" to="addGuest" />\n        <transition on="confirm" to="bookingConfirmed" />\n        <transition on="revise" to="enterBookingDetails" />\n        <transition on="cancel" to="bookingCancelled" />\n    </view-state>\n\n    <subflow-state id="addGuest" subflow="createGuest">\n        <transition on="guestCreated" to="reviewBooking">\n            <evaluate expression="booking.guests.add(currentEvent.attributes.guest)" />\n        </transition>\n        <transition on="creationCancelled" to="reviewBooking" />\n    </subflow-state>\n\n    <end-state id="bookingConfirmed" >\n        <output name="bookingId" value="booking.id" />\n    </end-state>\n\n    <end-state id="bookingCancelled" />\n\n</flow>\n\t\t\t\n')])])]),a("p",[e._v("The flow now calls a "),a("code",[e._v("createGuest")]),e._v(" subflow to add a new guest to the guest list.")])])}),[],!1,null,null,null);t.default=s.exports}}]);