流控制文件很简单，就是根元素是<view>,然后用<view-state>来代表一个一个的页面，用<transition>来代表从一个状态到另外一个状态的跳转，如果有动作要执行就会加在其中。

对于一个普通的java工程师，一般不需要超过1小时就可以熟知这个文件的编写方法,可查阅相关文档。

对于我们的flow,大体上如下所示：

因为图片实在太长，所以我没办法吧整个图片都截下来，这里只截取部分，对于flow定义的xml文件，我完整列在这里，可以供读者参考：

1. <?xml version="1.0" encoding="UTF-8"?> 
2. <flow xmlns="http://www.springframework.org/schema/webflow" 
3.       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
4.       xsi:schemaLocation="http://www.springframework.org/schema/webflow http://www.springframework.org/schema/webflow/spring-webflow-2.0.xsd"> 
5.      
6.      
7.     <!-- initialize all the variables in the flowScope --> 
8.     <on-start> 
9.         <evaluate expression="envProvisionInitService.initialize(flowRequestContext)" /> 
10.          
11.         <!-- initialize the flowScope variable:gridList to render the grid list --> 
12.         <!-- <evaluate expression="aerEnvGridService.listAppEnvRequests()" 
13.                    result="flowScope.gridListInfoJSONData" /> 
14.          -->            
15.         <!--  initialize the flowScope variable: availableServices to be used in hostvip info --> 
16.         <evaluate expression="defineHostVipService.listAvailableServices()" 
17.                    result="flowScope.availableServicesInfoJSONData" /> 
18.                     
19.         <set name="flowScope.isViewAction" value="false" type="boolean" /> 
20.                     
21.     </on-start> 
22.      
23.     <view-state id="aerEnvList" > 
24.      
25.         <on-render> 
26.           <evaluate expression="aerEnvGridService.listAppEnvRequests()" result="flowScope.gridListInfoJSONData" /> 
27.         </on-render> 
28.          
29.         <transition on="add" to="defineApp" /> 
30.         <transition on="confirm" to="aerRequestConfirm" > 
31.             <!-- fetch the data from web service and ready for populating data --> 
32.             <evaluate expression="aerEnvGridService.listEnvProvisionInfoByRequestId(requestParameters.requestId,flowRequestContext)"/> 
33.             <set name="flowScope.isViewAction" value="true" type="boolean" /> 
34.             <set name="flowScope.requestId" value="requestParameters.requestId" type="string"/> 
35.         </transition> 
36.         <transition on="approve" to="aerEnvList"> 
37.             <evaluate expression="adminService.approve(requestParameters.requestId)" /> 
38.         </transition> 
39.         <transition on="close" to="aerEnvList"> 
40.             <evaluate expression="adminService.close(requestParameters.requestId)" /> 
41.         </transition> 
42.         <transition on="reject" to="aerEnvList"> 
43.             <evaluate expression="adminService.reject(requestParameters.requestId)" /> 
44.         </transition> 
45.         <transition on="cmdb" to="aerEnvList"> 
46.             <evaluate expression="adminService.cmdb(requestParameters.requestId)" /> 
47.         </transition> 
48.     </view-state> 
49.  
50.     <view-state id="defineApp" >          
51.      
52.         <transition on="next" to="defineProject"> 
53.           <evaluate expression="defineAppService.createAppInfo(requestParameters.appInfoJSONData)" 
54.                    result="flowScope.appInfo"  /> 
55.           <set name="flowScope.appInfoJSONData" value="requestParameters.appInfoJSONData" type="string"/> 
56.           <set name="flowScope.hasAppInfoData" value="true" type="boolean"/> 
57.         </transition> 
58.         <transition on="cancel" to="aerEnvList" > 
59.             <evaluate expression="defineAppService.removeAppInfo(flowRequestContext)" /> 
60.             <evaluate expression="defineProjectService.removeProjectInfo(flowRequestContext)" /> 
61.             <evaluate expression="defineHostVipService.removeHostVipInfo(flowRequestContext)" /> 
62.             <evaluate expression="defineDBSrvService.removeDBServiceInfo(flowRequestContext)"/> 
63.         </transition> 
64.     </view-state> 
65.      
66.     <view-state id="defineProject"> 
67.         <transition on="previous" to="defineApp"/> 
68.          
69.         <transition on="next" to="defineHostVip">      
70.             <evaluate expression="defineProjectService.createProjectInfo(requestParameters.projectInfoJSONData)" 
71.                       result="flowScope.projectInfo"  /> 
72.             <set name="flowScope.projectInfoJSONData" value="requestParameters.projectInfoJSONData" type="string"/> 
73.             <set name="flowScope.hasProjectInfoData" value="true" type="boolean"/> 
74.         </transition> 
75.         <transition on="cancel" to="aerEnvList"> 
76.             <evaluate expression="defineAppService.removeAppInfo(flowRequestContext)" /> 
77.             <evaluate expression="defineProjectService.removeProjectInfo(flowRequestContext)" /> 
78.             <evaluate expression="defineHostVipService.removeHostVipInfo(flowRequestContext)" /> 
79.             <evaluate expression="defineDBSrvService.removeDBServiceInfo(flowRequestContext)"/> 
80.         </transition> 
81.     </view-state> 
82.      
83.     <view-state id="defineHostVip"> 
84.         <transition on="previous" to="defineProject"/> 
85.  
86.         <transition on="next" to="defineDBService"> 
87.             <evaluate expression="defineHostVipService.createHostVipInfo(requestParameters.hostVipInfoJSONData, flowRequestContext)" 
88.                       result="flowScope.hostVipInfo"  /> 
89.             <set name="flowScope.hostVipInfoJSONData" value="requestParameters.hostVipInfoJSONData" type="string"/> 
90.             <!-- additional set one field to pass the service list to next page(defineDBService.jsp) --> 
91.             <set name="flowScope.hasHostVipInfoData" value="true" type="boolean"/> 
92.             <set name="flowScope.services" value="requestParameters.services" type="string" /> 
93.         </transition> 
94.         <transition on="cancel" to="aerEnvList"> 
95.             <evaluate expression="defineAppService.removeAppInfo(flowRequestContext)" /> 
96.             <evaluate expression="defineProjectService.removeProjectInfo(flowRequestContext)" /> 
97.             <evaluate expression="defineHostVipService.removeHostVipInfo(flowRequestContext)" /> 
98.             <evaluate expression="defineDBSrvService.removeDBServiceInfo(flowRequestContext)"/> 
99.         </transition> 
100.     </view-state> 
101.      
102.     <view-state id="defineDBService"> 
103.         <transition on="previous" to="defineHostVip"/> 
104.      
105.         <transition on="next" to="aerRequestConfirm"> 
106.             <evaluate expression="defineDBSrvService.createDBServiceInfo(requestParameters.dbServiceInfoJSONData, flowRequestContext)" 
107.                       result="flowScope.dbServiceInfo"  /> 
108.             <set name="flowScope.dbServiceInfoJSONData" value="requestParameters.dbServiceInfoJSONData" type="string"/> 
109.             <set name="flowScope.hasDbServiceInfoData" value="true" type="boolean"/> 
110.             <set name="flowScope.isSubmitted" value="false" type="boolean"/> 
111.             <set name="flowScope.isViewAction" value="false" type="boolean" /> 
112.         </transition> 
113.         <transition on="cancel" to="aerEnvList"> 
114.             <evaluate expression="defineAppService.removeAppInfo(flowRequestContext)" /> 
115.             <evaluate expression="defineProjectService.removeProjectInfo(flowRequestContext)" /> 
116.             <evaluate expression="defineHostVipService.removeHostVipInfo(flowRequestContext)" /> 
117.             <evaluate expression="defineDBSrvService.removeDBServiceInfo(flowRequestContext)"/> 
118.         </transition> 
119.     </view-state> 
120.      
121.     <view-state id="aerRequestConfirm"> 
122.         <transition on="previous" to="defineDBService"/> 
123.         <transition on="submit" to="aerRequestSummary">       
124.             <evaluate expression="envProvisionRequestService.submitEnvProvisionRequest(flowRequestContext)" 
125.                       result="flowScope.submitResult"  /> 
126.         </transition> 
127.          
128.         <!--  
129.         <transition on="submit" to="aerRequestSummary"/> 
130.         --> 
131.         <transition on="cancel" to="aerEnvList"> 
132.             <evaluate expression="defineAppService.removeAppInfo(flowRequestContext)" /> 
133.             <evaluate expression="defineProjectService.removeProjectInfo(flowRequestContext)" /> 
134.             <evaluate expression="defineHostVipService.removeHostVipInfo(flowRequestContext)" /> 
135.             <evaluate expression="defineDBSrvService.removeDBServiceInfo(flowRequestContext)"/> 
136.         </transition> 
137.          
138.         <transition on="adminSubmit" to="aerRequestSummary">          
139.             <evaluate expression="envProvisionRequestService.updateEnvProvisionRequest(flowRequestContext)" 
140.                       result="flowScope.submitResult"  /> 
141.             <set name="flowScope.isViewAction" value="false" type="boolean" /> 
142.  
143.         </transition> 
144.          
145.         <!--  
146.         <transition on="submit" to="aerRequestSummary"/> 
147.         --> 
148.         <transition on="adminCancel" to="aerEnvList"> 
149.             <evaluate expression="defineAppService.removeAppInfo(flowRequestContext)" /> 
150.             <evaluate expression="defineProjectService.removeProjectInfo(flowRequestContext)" /> 
151.             <evaluate expression="defineHostVipService.removeHostVipInfo(flowRequestContext)" /> 
152.             <evaluate expression="defineDBSrvService.removeDBServiceInfo(flowRequestContext)"/> 
153.             <set name="flowScope.isViewAction" value="false" type="boolean" /> 
154.         </transition> 
155.          
156.          
157.         <transition on="noAdminOK" to="aerEnvList"> 
158.             <evaluate expression="defineAppService.removeAppInfo(flowRequestContext)" /> 
159.             <evaluate expression="defineProjectService.removeProjectInfo(flowRequestContext)" /> 
160.             <evaluate expression="defineHostVipService.removeHostVipInfo(flowRequestContext)" /> 
161.             <evaluate expression="defineDBSrvService.removeDBServiceInfo(flowRequestContext)"/> 
162.             <set name="flowScope.isViewAction" value="false" type="boolean" /> 
163.         </transition> 
164.          
165.          
166.          
167.         <!--add 4 event to distingush different partin the request confirmation page--> 
168.         <transition on="editApplicationInfo" to="defineApp"/> 
169.         <transition on="editProjectInfo"  to="defineProject"/> 
170.         <transition on="editHostVipInfo"  to="defineHostVip"/> 
171.         <transition on="editDBServiceInfo"  to="defineDBService"/> 
172.     </view-state> 
173.      
174.     <view-state id="aerRequestSummary"> 
175.         <transition on="ok" to="aerEnvList"> 
176.             <evaluate expression="defineAppService.removeAppInfo(flowRequestContext)" /> 
177.             <evaluate expression="defineProjectService.removeProjectInfo(flowRequestContext)" /> 
178.             <evaluate expression="defineHostVipService.removeHostVipInfo(flowRequestContext)" /> 
179.             <evaluate expression="defineDBSrvService.removeDBServiceInfo(flowRequestContext)"/> 
180.         </transition> 
181.     </view-state> 
182.      
183.     <end-state id="finish"/> 
184.              
185. </flow> 

这里，因为我们在这系列的第二篇文章中已经提及到，我们开启了包扫描机制，所以这些Spring的Bean在应用上下文创建的时候就已经实例化了，所以在这个流定义文件中可以轻松的使用这些bean.

 其实在做架构的时候，我曾和我们团队其他开发者讨论到为什么我们用spring web flow,其实这种页面跳转我们也可以不用web flow做，最后采用web flow的架构是基于以下几个原因：

众所周知，一般web应用的scope有 request，session,application,因为在很多配置页面上都有数据，并且这些数据都要共享，还比较大（那些传递的vo动辄100+字段）而且业务流程也比较复杂，而且这些数据还是有状态的，所以我们无法放在request scope上，而如果放在session scope上，又会加重系统的内存负担，所以我们需要一种介于request,session范围之间的scope,而spring web flow刚好提供了flow scope来精确的满足我们的需求，所以我们使用spring web flow.