This chapter shows how to integrate Web Flow into a Spring MVC web application. The booking-mvc sample application is a good reference for Spring MVC with Web Flow. This application is a simplified travel site that allows users to search for and book hotel rooms. The first step to using Spring MVC is to configure the DispatcherServlet in web.xml. You typically do this once per web application. The example below maps all requests that begin with /spring/ to the DispatcherServlet. An init-param is used to provide the contextConfigLocation. This is the configuration file for the web application. Spring MVC Dispatcher Servlet org.springframework.web.servlet.DispatcherServlet contextConfigLocation /WEB-INF/web-application-config.xml Spring MVC Dispatcher Servlet /spring/* ]]> The DispatcherServlet maps requests for application resources to handlers. A flow is one type of handler. The first step to dispatching requests to flows is to enable flow handling within Spring MVC. To this, install the FlowHandlerAdapter: ]]> Once flow handling is enabled, the next step is to map specific application resources to your flows. The simplest way to do this is to define a FlowIdHandlerMapping: ]]> Configuring this mapping allows the Dispatcher to map application resource paths to flows in a flow registry. For example, accessing the resource path /hotels/booking would result in a registry query for the flow with id hotels/booking. If a flow is found with that id, that flow will handle the request. If no flow is found, the next handler mapping in the Dispatcher's ordered chain will be queried or a "noHandlerFound" response will be returned. When a valid flow mapping is found, the FlowHandlerAdapter figures out whether to start a new execution of that flow or resume an existing execution based on information present the HTTP request. There are a number of defaults related to starting and resuming flow executions the adapter employs: HTTP request parameters are made available in the input map of all starting flow executions. When a flow execution ends without sending a final response, the default handler will attempt to start a new execution in the same request. Unhandled exceptions are propagated to the Dispatcher unless the exception is a NoSuchFlowExecutionException. The default handler will attempt to recover from a NoSuchFlowExecutionException by starting over a new execution. Consult the API documentation for FlowHandlerAdapter for more information. You may override these defaults by subclassing or by implementing your own FlowHandler, discussed in the next section. FlowHandler is the extension point that can be used to customize how executions of a flow are managed in a HTTP servlet environment. A FlowHandler is used by the FlowHandlerAdapter and responsible for: Returning the id of a flow definition to execute Creating the input to pass new executions of that flow as they are started Handling outcomes returned by executions of that flow as they end Handling any exceptions thrown by executions of that flow as they occur These responsibilities are illustrated in the definition of the org.springframework.mvc.servlet.FlowHandler interface: public interface FlowHandler { public String getFlowId(); public MutableAttributeMap createExecutionInputMap(HttpServletRequest request); public String handleExecutionOutcome(FlowExecutionOutcome outcome, HttpServletRequest request, HttpServletResponse response); public String handleException(FlowException e, HttpServletRequest request, HttpServletResponse response); } To implement a FlowHandler, subclass AbstractFlowHandler. All these operations are optional, and if not implemented the defaults will apply. You only need to override the methods that you need. Specifically: Override getFlowId(HttpServletRequest) when the id of your flow cannot be directly derived from the HTTP request. By default, the id of the flow to execute is derived from the pathInfo portion of the request URI. For example, http://localhost/app/hotels/booking?hotelId=1 results in a flow id of hotels/booking by default. Override createExecutionInputMap(HttpServletRequest) when you need fine-grained control over extracting flow input parameters from the HttpServletRequest. By default, all request parameters are treated as flow input parameters. Override handleExecutionOutcome when you need to handle specific flow execution outcomes in a custom manner. The default behavior sends a redirect to the ended flow's URL to restart a new execution of the flow. Override handleException when you need fine-grained control over unhandled flow exceptions. The default behavior attempts to restart the flow when a client attempts to access an ended or expired flow execution. Any other exception is rethrown to the Spring MVC ExceptionResolver infrastructure by default. A common interaction pattern between Spring MVC And Web Flow is for a Flow to redirect to a @Controller when it ends. FlowHandlers allow this to be done without coupling the flow definition itself with a specific controller URL. An example FlowHandler that redirects to a Spring MVC Controller is shown below: Since this handler only needs to handle flow execution outcomes in a custom manner, nothing else is overridden. The bookingConfirmed outcome will result in a redirect to show the new booking. Any other outcome will redirect back to the hotels index page. To install a custom FlowHandler, simply deploy it as a bean. The bean name must match the id of the flow the handler should apply to. ]]> With this configuration, accessing the resource /hotels/booking will launch the hotels/booking flow using the custom BookingFlowHandler. When the booking flow ends, the FlowHandler will process the flow execution outcome and redirect to the appropriate controller. A FlowHandler handling a FlowExecutionOutcome or FlowException returns a String to indicate the resource to redirect to after handling. In the previous example, the BookingFlowHandler redirects to the booking/show resource URI for bookingConfirmed outcomes, and the hotels/index resource URI for all other outcomes. By default, returned resource locations are relative to the current servlet mapping. This allows for a flow handler to redirect to other Controllers in the application using relative paths. In addition, explicit redirect prefixes are supported for cases where more control is needed. The explicit redirect prefixes supported are: servletRelative: - redirect to a resource relative to the current servlet contextRelative: - redirect to a resource relative to the current web application context path serverRelative: - redirect to a resource relative to the server root http:// or https:// - redirect to a fully-qualified resource URI These same redirect prefixes are also supported within a flow definition when using the externalRedirect: directive in conjunction with a view-state or end-state; for example, view="externalRedirect:http://springframework.org" Web Flow 2 maps selected view identifiers to files located within the flow's working directory unless otherwise specified. For existing Spring MVC + Web Flow applications, an external ViewResolver is likely already handling this mapping for you. Therefore, to continue using that resolver and to avoid having to change how your existing flow views are packaged, configure Web Flow as follows: ]]>