Accessing data services overview

Unlike a set of HTML templates created using JSPs and servlets, ASP, PHP, or CFML, Flex separates client code from server code. The application user interface is compiled into a binary SWF file that is sent to the client.

When the application makes a request to a data service, the SWF file is not recompiled and no page refresh is required. The remote service returns only data. Flex binds the returned data to user interface components in the client application.

For example, in Flex, when a user clicks a Button control in an application, client-side code calls a web service. The result data from the web service is returned into the binary SWF file without a page refresh. Thus, the result data is available to use as dynamic content in the application.

<?xm l version="1.0" encoding="utf-8"?> 
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009" 
    xmlns:s="library://ns.adobe.com/flex/spark" 
    xmlns:mx="library://ns.adobe.com/flex/halo" minWidth="1024" minHeight="768" xmlns:employeesservice="services.employeesservice.*" xmlns:valueObjects="valueObjects.*"> 
 
    <fx:Declarations> 
        <s:WebService 
            id="RestaurantSvc" 
        wsdl="http://examples.adobe.com/flex3app/restaurant_ws/RestaurantWS.xml?wsdl" /> 
        <s:CallResponder id="getRestaurantsResult" 
            result="restaurants = getRestaurantsResult.lastResult as Restaurant"/> 
    </fx:Declarations> 
 
    <fx:Script> 
        <![CDATA[ 
            import mx.controls.Alert; 
 
            protected function b1_clickHandler(event:MouseEvent):void { 
                getRestaurantsResult.token = RestaurantWS.getRestaurantss(); 
            } 
        ]]> 
    </fx:Script> 
. . . 
    <s:Button id="b1" label="GetRestaurants" click="button_clickHandler(event)"/> 
 

Compare this Flex example to the following example, which shows JSP code for calling a web service using a JSP custom tag. When a user requests the JSP, the web service request is made on the server instead of on the client. The result is used to generate content in the HTML page. The application server regenerates the entire HTML page before sending it back to the user's web browser.

<%@ taglib prefix="web" uri="webservicetag" %> 
 
<% String str1="BRL"; 
String str2="USD";%> 
 
<!-- Call the web service. --> 
<web:invoke 
    url="http://www.itfinity.net:8008/soap/exrates/default.asp" 
    namespace="http://www.itfinity.net/soap/exrates/exrates.xsd" 
    operation="GetRate" 
    resulttype="double" 
    result="myresult"> 
    <web:param name="fromCurr" value="<%=str1%>"/> 
    <web:param name="ToCurr" value="<%=str2%>"/> 
</web:invoke> 
 
<!-- Display the web service result. --> 
<%= pageContext.getAttribute("myresult") %>

Another difference between Flex and other web application technologies is that you never communicate directly with a data source in Flex. You use a data access component to connect to a remote service and to interact with the server-side data source.

The following example shows a ColdFusion page that accesses a data source directly:

... 
<CFQUERY DATASOURCE="Dsn" 
    NAME="myQuery"> 
    SELECT * FROM table 
</CFQUERY> 
...

To get similar functionality in Flex, use an HTTPService, a web service, or a RemoteObject component to call a server-side object that returns results from a data source.

Flex is an event driven technology. A user action or a program event can trigger access to a service. For example, a user clicking a button is a user action event that can be used to trigger a service call. An example of a program event is when the application completes the creation of a user interface component such as a DataGrid. The creationComplete event for the DataGrid can be used to call a remote service to populate the DataGrid.

Service calls in Flex are asynchronous. The client application does not have to wait for returned data. Asynchronous service calls are useful when retrieving or updating large sets of data. The client application is not blocked waiting for the data to be retrieved or updated.

Data returned from a service call is stored in a CallResponder that you associate with the service call. User interface components then use data binding to retrieve the returned data from the CallResponder.

Data binding in Flex allows you to dynamically update a user interface component with a data source. For example, a Flex component can associate its text attribute with the lastResult attribute of a CallResponder. When the data in the CallResponder changes, the Flex component automatically updates.

Flex also implements two-way data binding. With two-way data binding, when data changes in either the Flex component or the data source, the corresponding data source or Flex component automatically updates. Two-way data binding is useful when updating remote data from user inputs to a Form component or a Flex data component.

Use the following workflow when using Flash Builder to create an application that accesses data services.

1. Depending on your circumstances, you start by connecting to a data service or by building the user interface.

   Connect to remote service. If you start by connecting to the remote service, you then build the user interface.

   Build user interface. If you start by building the user interface, you then connect to the remote service.

   Note: Where you start is a matter of personal preference. For example, if you already have a user interface design planned, you can build the user interface first. Conversely, you can connect to the data first and let Flash Builder assist you in generating application components.

2. Bind data operations to application components.

3. (Optional) Manage the retrieval and update of data.

   Flash Builder tools allow you to implement the paging of returned data and coordinate the update of sets of data.

   When returning large amounts data records, you typically implement paging to retrieve a set of records on an “as needed” basis.

   For applications that updates several records, you can implement data management features. Data Management features include:

   • Commit functionality to update changed records simultaneously

   • An undo mechanism to revert changes before they are written to the server

   • Code generation that automatically updates user interface components as records are added, deleted, or changed

4. Run the application and monitor the data flow.

   When the application is complete, run the application to view it in operation. Use the Flash Builder Network Monitor to view data passed between the application and the service. The Network Monitor is useful for diagnosing errors and analyzing performance.

   Flash Builder also provides robust debugging and profiling environments. The Network Monitor and Flash Profiler are available with Flash Builder Premium.

Flash Builder wizards and tools support access to the following type of service implementations:

• PHP services

• ColdFusion services

• BlazeDS

• LiveCycle Data Services

• HTTP (REST-style) services

• Web services (SOAP)

• Static XML files

If you need tooling support for additional types of services, such as Ruby on Rails, you can extend the Flash Builder implementation. See Flash Builder Extensibility Reference.

By default, Adobe Flash Player blocks access to any host that is not exactly equal to the one used to load an application. If you do not use a server side application, such as LiveCycle Data Services or BlazeDS, to proxy requests, an HTTP service or web service must either be on the server hosting your application, or the remote server that hosts the HTTP or web service must define a crossdomain.xml file. A crossdomain.xml file provides a way for a server to indicate that its data and documents are available to SWF files served from certain domains, or from all domains. The crossdomain.xml file must be in the web root of the server that the application is contacting.

Use HTTPService components to send HTTP GET or POST requests and include the data from HTTP responses in a client application. If you are using Flex to build desktop applications (runs in Adobe AIR®), HTTP PUT and DELETE are supported.

If you use LiveCycle Data Services or BlazeDS, you can use an HTTPProxyService, which allows you to to use additional HTTP methods. With an HTTPProxyService, you can send GET, POST, HEAD, OPTIONS, PUT, TRACE, or DELETE requests.

An HTTP service can be any HTTP URI that accepts HTTP requests and sends responses. Another common name for this type of service is a REST-style web service. REST stands for Representational State Transfer and is an architectural style for distributed hypermedia systems.

HTTPService components are a good option when you cannot expose the same functionality as a SOAP web service or a remote object service. For example, you can use HTTPService components to interact with JavaServer Pages (JSPs), servlets, and ASP pages that are not available as web services or Remoting Service destinations.

When you call the HTTPService object’s send() method, it makes an HTTP request to the specified URI, and an HTTP response is returned. Optionally, you can pass arguments to the specified URI.

Flash Builder provides workflows that allow you to interactively connect to HTTP services. For more information, see Accessing HTTP services.

WebService components let you access SOAP web services, which are software modules with methods. Web service methods are commonly called operations. Web service interfaces are defined using Web Services Description Language (WSDL). Web services provide a standards-compliant way for software modules that are running on various platforms to interact with each other. For more information about web services, see the web services section of the World Wide Web Consortium website at www.w3.org/2002/ws/.

Client applications can interact with web services that define their interfaces in a Web Services Description Language (WSDL) document, which is available as a URL. WSDL is a standard format for describing the messages that a web service understands, the format of its responses to those messages, the protocols that the web service supports, and where to send messages.

Flex supports WSDL 1.1, which is described at www.w3.org/TR/wsdl. Flex supports both RPC-encoded and document-literal web services.

Flex supports web service requests and results that are formatted as SOAP messages and are transported over HTTP. SOAP provides the definition of the XML-based format that you can use for exchanging structured and typed information between a web service client, such as an application built with Flex, and a web service.

You can use a WebService component to connect to a SOAP-compliant web service when web services are an established standard in your environment. WebService components are also useful for objects that are within an enterprise environment, but not necessarily available on the source path of the web application.

Flash Builder provides workflows that allow you to interactively connect to web services. For more information, see Accessing web services.

Remote object services let you access business logic directly in its native format rather than formatting it as XML, as you do with REST-style services or web services. This saves you the time required to expose existing logic as XML. Another benefit of remote object services is the speed of communication across the wire. Data exchanges still happen over HTTP or https, but the data itself is serialized into a binary representation. Using RemoteObject components results in less data going across the wire, reduced client-side memory usage, and reduced processing time.

ColdFusion, PHP, BlazeDS, and LiveCycle Data Services can use server-side typing when accessing data on the server. The client application accesses a Java object, ColdFusion component (which is a Java object internally), or PHP class directly by remote invocation of a method on a designated object. The object on the server uses its own native data types as arguments, queries a database with those arguments, and returns values in its native data types.

When server-side typing is not available, Flash Builder has tools to implement client-side typing. Use the Flash Builder to configure and define types for data returned from the service. Client-side typing allows the client application to query a database and retrieve properly typed data. Client-side typing is required for any service that does not define the type of data returned by the service.

Flash Builder provides workflows that allow you to interactively connect to remote object services. For more information, see Connecting to data services.