Chapter 37. SpringAir - Reference Application

The SpringAir sample application demonstrates a selection of Spring.NET's powerful features making a .NET programmer's life easier. It demonstrates the following features of Spring.Web

The application models a flight reservation system where you can browse flights, book a trip and even attach your own clients by leveraging the web services exposed by the SpringAir application.

All pages within the application are fully Spring managed. Dependencies get injected as configured within a Spring Application Context. For NET 1.1 it shows how to apply centrally managed layouts to all pages in an application by using master pages - a well-known feature from NET 2.0.

When selecting your flights, you are already experiencing a fully localized form. Select your preferred language from the bottom of the form and see, how the new language is immediately applied. As soon as you submit your desired flight, the submitted values are automatically unbound from the form onto the application's data model by leveraging Spring.Web's support for Data Binding. With Data Binding you can easily associate properties on your PONO model with elements on your ASP.NET form.

The application is located in the installation directory under 'examples/SpringAir. The directory 'SpringAir.Web.2003' contains the .NET 1.1 version of the application and the directory 'SpringAir.Web.2005' contains the .NET 2.0 version. For .NET 1.1 you will need to create a virtual directory named 'SpringAir.2003' using IIS Administrator and point it to the following directory examples\Spring\SpringAir\src\SpringAir.Web.2003. The solution file for .NET 1.1 is examples\Spring\SpringAir\SpringAir.2003.sln. For .NET 2.0 simply open the solution examples\Spring\SpringAir\SpringAir.2005.sln. Set your startup project to be SpringAir.Web and the startpage to .\Web\Home.aspx

The web project's top level Web.config configures the IoC container that is used within the web application. You do not need to explicitly instantiate the IoC container. The important parts of that configuration are shown below

<spring>
    <parsers>
        <parser type="Spring.Data.Config.DatabaseNamespaceParser, Spring.Data" />
    </parsers>

    <context>
        <resource uri="~/Config/Aspects.xml"/>
        <resource uri="~/Config/Web.xml"/>
        <resource uri="~/Config/Services.xml"/>
      
        <!-- TEST CONFIGURATION -->

       <resource uri="~/Config/Test/Services.xml"/>
       <resource uri="~/Config/Test/Dao.xml"/>
      
       <!-- PRODUCTION CONFIGURATION -->

       <!--
       <resource uri="~/Config/Production/Services.xml"/>
       <resource uri="~/Config/Production/Dao.xml"/>
       -->
    </context>
</spring>

In this example there are separate configuration files for test and production configuration. The Services.xml file is in fact the same between the two, and the example will be refactored in future to remove that duplication. The Dao layer in the test configuration is an in-memory version, faking database access, whereas the production version uses an ADO.NET based solution.

The pages that comprise the application are located in the directory 'Web/BookTrip'. In that directory is another Web.config that is responsible for configuring that directory's .aspx pages. There are three main pages in the flow of the application.

The XML configuration to configure the TripForm form is shown below

      <object type="TripForm.aspx" parent="standardPage">
        <property name="BookingAgent" ref="bookingAgent" />
        <property name="AirportDao" ref="airportDao" />
        <property name="TripValidator" ref="tripValidator" />
        <property name="Results">
          <dictionary>
            <entry key="displaySuggestedFlights" value="redirect:SuggestedFlights.aspx" />
          </dictionary>
        </property>
      </object>

As you can see the various services it needs are set using standard DI techniques. The Results property externalizes the page flow, redirecting to the next page in the flow, SuggestedFlights. The 'parent' attribute lets this page inherit properties from a template. The is located in the top level Web.config file, packaged under the Config directory. The standardPage sets up properties of Spring's base page class, from which all the pages in this application inherit from. (Note that to perform only dependency injection on pages you do not need to inherit from Spring's Page class).

The TripForm page demonstrates the bi-directional data binding features. A Trip object is used to back the information of the form. The family of methods that are overridden to support the bi-directional data binding are listed below.

    protected override void InitializeModel()
    {
        trip = new Trip();
        trip.Mode = TripMode.RoundTrip;
        trip.StartingFrom.Date = DateTime.Today;
        trip.ReturningFrom.Date = DateTime.Today.AddDays(1);
    }

    protected override void LoadModel(object savedModel)
    {
        trip = (Trip)savedModel;
    }

    protected override object SaveModel()
    {
        return trip;
    }

    protected override void InitializeDataBindings()
    {
        BindingManager.AddBinding("tripMode.Value", "Trip.Mode");
        BindingManager.AddBinding("leavingFromAirportCode.SelectedValue", "Trip.StartingFrom.AirportCode");
        BindingManager.AddBinding("goingToAirportCode.SelectedValue", "Trip.ReturningFrom.AirportCode");
        BindingManager.AddBinding("leavingFromDate.SelectedDate", "Trip.StartingFrom.Date");
        BindingManager.AddBinding("returningOnDate.SelectedDate", "Trip.ReturningFrom.Date");
    }

This is all you need to set up in order to have values from the Trip object 'marshaled' to and from the web controls. The InitializeDataBindings method set this up, using the Spring Expression Language to define the UI element property that is associate with the model (Trip) property.

The method called when the Search button is clicked will perform validation. If validation succeeds as well as additional business logic checks, the next page in the flow is loaded. This is shown in the code below. Notice how much cleaner and more business focused the code reads than if you were using standard ASP.NET APIs.

    protected void SearchForFlights(object sender, EventArgs e)
    {
        if (Validate(trip, tripValidator))
        {
            FlightSuggestions suggestions = this.bookingAgent.SuggestFlights(Trip);
            if (suggestions.HasOutboundFlights)
            {
                Session[Constants.SuggestedFlightsKey] = suggestions;
                SetResult(DisplaySuggestedFlights);
            }
        }
    }

The 'Validate' method of the page takes as arguments the object to validate and a IValidator instance. The TripForm property TripValidator is set via dependency injection (as shown above). The validation logic is defined declaratively in the XML configuration file and is shown below.

   <v:group id="tripValidator">

    <v:required id="departureAirportValidator" test="StartingFrom.AirportCode">
				  <v:message id="error.departureAirport.required" providers="departureAirportErrors, validationSummary"/>
				</v:required>

			  <v:group id="destinationAirportValidator">
				  <v:required test="ReturningFrom.AirportCode">
				    <v:message id="error.destinationAirport.required" providers="destinationAirportErrors, validationSummary"/>
				  </v:required>
				  <v:condition test="ReturningFrom.AirportCode != StartingFrom.AirportCode" when="ReturningFrom.AirportCode != ''">
				    <v:message id="error.destinationAirport.sameAsDeparture" providers="destinationAirportErrors, validationSummary"/>
				  </v:condition>
			  </v:group>

				<v:group id="departureDateValidator">
					<v:required test="StartingFrom.Date">
				    <v:message id="error.departureDate.required" providers="departureDateErrors, validationSummary"/>
				  </v:required>
					<v:condition test="StartingFrom.Date >= DateTime.Today" when="StartingFrom.Date != DateTime.MinValue">
				    <v:message id="error.departureDate.inThePast" providers="departureDateErrors, validationSummary"/>
					</v:condition>
				</v:group>

				<v:group id="returnDateValidator" when="Mode == 'RoundTrip'">
					<v:required test="ReturningFrom.Date">
				    <v:message id="error.returnDate.required" providers="returnDateErrors, validationSummary"/>
				  </v:required>
					<v:condition test="ReturningFrom.Date >= StartingFrom.Date" when="ReturningFrom.Date != DateTime.MinValue">
				    <v:message id="error.returnDate.beforeDeparture" providers="returnDateErrors, validationSummary"/>
				  </v:condition>
				</v:group>

			</v:group>

The validation logic has 'when' clauses so that return dates can be ignored if the Mode property of the Trip object is set to 'RoundTrip'.

Both image and text based internationalization are supported. You can see this in action by clicking on the English, Srpski, or Српски links on the bottom of the page.

The class BookingAgent that was used by the TripForm class is a standard .NET class, i.e no WebMethod attributes are on any of its methods. Spring can expose this object as a web service by declaring the following XML defined in the top level Config/Services.xml file

  <object id="bookingAgentWebService" type="Spring.Web.Services.WebServiceExporter, Spring.Web">
    <property name="TargetName" value="bookingAgent"/>
    <property name="Name" value="BookingAgent"/>
    <property name="Namespace" value="http://SpringAir/WebServices"/>
    <property name="Description" value="SpringAir Booking Agent Web Service"/>
    <property name="MemberAttributes">
      <dictionary>
        <entry key="SuggestFlights">
          <object type="System.Web.Services.WebMethodAttribute, System.Web.Services">
            <property name="Description" value="Gets those flight suggestions that are applicable for the supplied trip."/>
          </object>
        </entry>
        <entry key="Book">
          <object type="System.Web.Services.WebMethodAttribute, System.Web.Services">
            <property name="Description" value="Goes ahead and actually books what up until this point has been a transient reservation."/>
          </object>
        </entry>
        <entry key="GetAirportList">
          <object type="System.Web.Services.WebMethodAttribute, System.Web.Services">
            <property name="Description" value="Return a collection of all those airports that can be used for the purposes of booking."/>
          </object>
        </entry>
      </dictionary>
    </property>
  </object>