Spring Web Flow yes Spring Subprojects of the framework , The function is to make the program run according to the specified process .
1 Installation configuration Spring Web Flow
although Spring Web Flow yes Spring Subprojects of the framework , But it's not Spring Part of the frame , So before building process based applications , You need to add Spring Web Flow The required jar package . Download at ：http://www.springframework.org/webflow
Spring Web Flow It's about building and Spring MVC Based on . This means that all process requests need to go through Spring MVC Of DispatcherServlet. So we need to be able to Spring In the context of the application .
FlowRegistry It's for storage. flow The warehouse of , Each definition flow Of XML After the document is parsed , Will be assigned a unique id , And FlowDefinition The form of the object is stored in FlowResigtry in .
<webflow:flow-location path="/WEB-INF/flows/shopping.xml" id=”shopping”/>
Every flow Must have id To mark , If omitted in configuration , Then the flow default id Will be the definition file （xml file ） Remove the suffix from the file name of （ For example, in this case, if you remove id="shopping", that flow Of id Namely shopping.xml Remove the suffix .xml After shopping As id）.
FlowExecutor yes Spring Web Flow A core interface of , Start something flow , It's all through this interface . From a configuration point of view , Just make sure there's a FlowExecutor That's all right. , Spring Web Flow The default behavior of is enough .
<webflow:flow-executor id="flowExecutor" />
1.3 Spring Web Flow How to communicate with Spring Web MVC Integrated ？
Request sent by client , First of all, I'll let you know servlet Containers （ In this tutorial example is Tomcat ） receive , servlet The container will find the corresponding application （ In this tutorial is CartApp ）, According to web.xml The configuration of is found to meet the mapping conditions servlet To deal with it . Spring Web MVC To handle requests in servlet yes DispatcherServlet , If the requested path satisfies DispatcherServlet The mapping condition of , be DispatcherServlet Will find out Spring IoC Everything in the container HandlerMapping , According to these HandlerMapping The best match of all handler （ In general, it's controller , I.e. controller ） To process requests . When Controller Finished processing , It usually returns a view （ View ） Name ,DispatcherServlet According to this view Find the corresponding view resource and return it to the client .
Make clear Spring Web MVC After the process of processing the request , Basically, we can understand the need to integrate Spring Web MVC And Spring Web Flow The configuration needed . In order to make the client's request become the execution of a flow Request , To solve the following problems ：
- It needs to be somewhere HandlerMapping Configuration is responsible for processing flow Requested handler （ or controller ）
- The handler （ or controller ） Be responsible for starting the specified flow
- flow The views involved during and after execution should be presented to the client
1.4 FlowHandler and FlowController
Now? , A receiving execution is needed flow Request , And then start the corresponding flow Of handler （ processor ）, Spring Web Flow 2.0 Two options are offered . The first solution is to write and implement FlowHandler The class of the interface , Let this class implement this function . The second option is to use a ready-made FlowController The controller . The first is more flexible , In many cases, it may be the only choice , But for each flow We need to write the corresponding FlowHandler . The examples in this tutorial take the second approach , Yes FlowHandler Please refer to Spring Web Flow 2.0 The documentation that comes with you . FlowController It's actually an adapter , In general , We just have to understand FlowController Depending on the end of the client request , Find out the corresponding flow To execute . To configure FlowController Just specify FlowExecutor that will do .
<bean id="flowController" class="org.springframework.webflow.mvc.servlet.FlowController">
<property name="flowExecutor" ref="flowExecutor"/>
In addition, it needs to be done in HandlerMapping Named in the /shopping.do Request by the flowController To deal with it ：
<!-- /shopping.do Request by the flowController To deal with it -->
<value> /shopping.do=flowController </value>
<span style="white-space:pre"> </span>......
1.5 FlowBuilder Services
flow-builder-services Property configuration indicates that in this flow-registry “ Warehouse ” Inside flow Some basic characteristics of , for example , Yes, it is Unified EL still OGNL 、 model （ Model ） Whether the data in the object needs to be converted before being displayed , wait . In this example , We need to be in flow-builder-services Property indicates Spring Web Flow What's used in view , from Spring Web MVC Of “ View Resolver ” Search for , from Spring Web MVC Of “ View Class” Parsing , Finally, it is presented to the user .
<!-- FlowRegistry It's for storage. flow The warehouse of , Each definition flow Of XML After the document is parsed , Will be assigned a unique id , And FlowDefinition The form of the object is stored in FlowRes igtry in -->
<!-- all flow Its location is configured here , flow-builder-services Used for configuration flow Characteristics of -->
<webflow:flow-registry id="flowRegistry" flow-builder-services="flowBuilderServices">
<webflow:flow-location path="/WEB-INF/flows/shopping.xml" id="shopping" />
<webflow:flow-location path="/WEB-INF/flows/addToCart.xml" id="addToCart" />
<!--Web Flow The view in the MVC Frame view technology to present -->
<webflow:flow-builder-services id="flowBuilderServices" view-factory-creator="mvcViewFactoryCreator" />
<!-- To specify MVC Framework of the view resolver , Used by view Find resources by name -->
<bean id="mvcViewFactoryCreator" class="org.springframework.webflow.mvc.builder.MvcViewFactoryCreator">
<property name="viewResolvers" ref="viewResolver" />
All of these configurations are for two purposes ： One is to turn the client's request into flow Implementation , Second, let flow In the process of execution 、 Or the view obtained after execution can be returned to the client .
2 Spring Web Flow The components of
Spring Web Flow in , The process is made up of 3 It's defined by two main elements ： state 、 Transfer and process data .
Spring Web Flow Defined 5 There are two different types of States （state）—— Behavior 、 Decision making 、 end 、 Subprocesses and view States .
In addition to the end state , Other states can be changed to other states , Generally by defining transitions in state （transition） To achieve the transition to other states , The occurrence of transformation is generally determined by events （event） To trigger .
2.1.1 View state
View state is used to present information for users and to participate in the process . The actual view can be of any type , But usually with JSP To achieve .
In the process XML In file , Use <view-state> Define view state .
<view-state id="viewCart" view="viewCart">
<transition on="submit" to="viewOrder">
2.1.2 State of conduct
The behavior state is that the program itself is performing a task , In general, it will trigger Spring Managed Bean And transfer to another state according to the return result of the method .
In the process XML In file , Use <action-state> Define behavior states .
<evaluate expression="cart.addItem(productService.getProduct(productId))" />
<transition to="productAdded" />
<action-state> There's usually one of them <evaluate> Elements ,<evaluate> The element specifies what the behavior state does .
2.1.3 Decision state
The decision state can produce two branches when the process is executed . Judge a Boolean Expression of type , Then choose one of the two states .
In the process XML In file , Use <decision-state> Define the decision state .
<if test="flowScope.ticketGrantingTicketId neq null" then="hasServiceCheck" else="gatewayRequestCheck" />
2.1.4 Sub process status
The subprocess state is used to invoke another process in a running process .
In the process XML In file , Use <subflow-state> Define sub process state .
<subflow-state id="addProductToCart" subflow="addToCart">
<transition on="productAdded" to="viewCart" />
2.1.5 End state
The end state is used to end a process .
In the process XML In file , Use <end-state> Define the end state .
<end-state id="returnToIndex" view="externalRedirect:servletRelative:/index.jsp">
If you end up with a subprocess , Then the process will start from the parent process <subflow-state> Continue to execute , Sub process <end-state> Of ID Will trigger the parent process <subflow-state> Of transition.
If <end-state> Set up view attribute , The specified view will be rendered , Add “externalRedirect:” The prefix will be redirected to a page outside the process , And add “flowRedirect:” Redirect to another process .
If the ending process is neither a subprocess nor specified view attribute , Then the process will just end , The browser will load the basics of the process URL Address , Start a new process instance .
In addition to the end state in the process , Each of the remaining states needs to have at least one transition , Only in this way can we know where the process will go once this state is completed . States can also have multiple transitions .
Transfer use <transition> Elements to define , It will be used as various state elements （<action-state> etc. ） Child elements .
<transition on="addToCart" to="addProductToCart" />
attribute to Used to specify the next state of the process .
attribute on Used to specify the event that triggers the transition .（ One more on-exception Properties are not given in this example , It is used to specify the exception that triggers the transition ）
When multiple states use the same transition , You can set up a global transition to simplify the code .
<transition on="cancelShopping" to="returnToIndex"/>
After defining the global transfer , All States in the process will have this by default cancelShopping Transfer .
2.3 Process data
The process state may need to “ Piggyback ” Some of the data , These data are process data , Process data is stored in variables , Variables can be created in many forms , And you can set the scope .
2.3.1 Declare variables
The simplest form of creating variables in a process is to use <var> Elements ：
<var name="mycart" class="samples.webflow.Cart" />
The code above creates a Cart Instance and put it in a place called mycart Variables in .
Use <evaluate> perhaps <set> Elements can also create variables ：
<evaluate result="conversationScope.cart" expression="mycart"/>
<set name="conversationScope.cart" value="mycart"/>
<evaluate> Elements and <set> The elements are very similar , It's all the result of setting the variable to the expression evaluation . Here's the variable cart The scope of is conversationScope, Next, let's talk about the scope of process data .
2.3.2 Define the scope of process data
Spring Web Flow Defined 5 Species scope , The following table ：
|Range||Scope and visibility|
|Conversation||Create... At the beginning of the highest level process , Destroy at the end of the highest level process . Shared by the highest level process and all its subprocesses|
|Flow||Create... When the process starts , Destroy at the end of the process . Only visible in the process of creating it|
|Request||Create... When a request enters the process , Destroy on process return|
|Flash||Create... When the process starts , Destroy at the end of the process . After rendering in view state , It will also be removed|
|View||Create... When entering view state , Destroy when this state exits . Visible only in view state|
When using <var> When an element declares a variable , The variable is always Flow Scoped , That is to say Flow Define variables in scope . When using <set> or <evaluate> when , Scope through name or result The prefix of the property specifies .
Reference resources ：
Reprint please indicate the source
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