User Notification is the first aspect of cloud push that you must understand. When a user is actively working with an application on a mobile device, the user interface (UI) of that application can continually update information displayed to the user as the state of the application changes. For instances, an email application can update the number of emails in the inbox as new emails arrive. When the user is not actively using an application, that application can not rely on its UI to convey new information to the user, because the UI is not visible at the moment. Mobile devices provide a number of ways to alert the user of a state change occurring in an inactive application. A status bar can display an alerting icon, or a sound or vibration can occur. For instance, an email application can display an icon indicating that new mail has arrived since the user last viewed her inbox.
When a user notification is the result of some state change coming from outside the device over a network connection, we refer to that as Cloud Push. The dominant mobile platforms all provide Cloud Push mechanisms that can be incorporated into an application. Specifically, the mechanisms are:
These mechanisms can be integrated directly with a native mobile application to achieve appropriate user notifications triggered from the network cloud.
Beyond these proprietary push mechanisms, other common network protocols can be considered for cloud push notification, such as:
- SMS text messaging
These mechanisms have the advantage of ubiquitous support across mobile platforms, relying on the device's built in support for these protocols, but won't necessarily integrate tightly with the native application.
The concept of push in web applications was completely foreign until the advent of Ajax, and more specifically Ajax Push. Ajax Push makes pushing asynchronous state changes to a web application possible, so an active web application can behave much like an active native application, pushing state changes to the UI in a spontaneous fashion as the state of the application changes.
When a web application becomes inactive, not only is the UI unavailable, the network connection back to the server is also unavailable, so Ajax Push connections cannot be maintained. In order to support cloud push to web applications, ICEmobile-Faces augments Ajax Push with a priority push mechanism that utilizes a cloud push connector to a native [Device Container]. Even when the web application is idle, Ajax Push can send priority notifications over a cloud push connector to the device, and alert the user with standard user notification mechanisms on the device.
We now review the Ajax Push mechanism with respect to active and inactive web applications.
When the web application is active, the Ajax Push mechanism relies on HTTP and the notification protocol in ICEpush, which uses reverse polling over a blocking connection to facilitate asynchronous page updates. The basic process is illustrated below.
- Some state change in the application triggers an Ajax Push event.
- ICEpush notification is delivered to the browser client over a dedicated ICEpush connection.
- Notification at client browser causes a JSF Ajax request with an empty execute phase.
- Render phase captures new state of client, and Direct-to-DOM Rendering delivers incremental page updates to client.
Once an ICEfaces page loads in the ICEmobile device container, the container notifies the ICEpush bridge, describing the cloud push connector type/credentials associated with the client device (if there is one). When the web application goes inactive on the device, the ICEpush bridge connection is parked on the server for that client's session. While the connection remains parked, any priority push requests that occur for that client will be sent via the specified cloud connector, to be received at the device container (in the case of a platform-specific connector), or by the email client (in the case of an email connector). In the case of the device container, the cloud push will result in a user notification carrying a specific subject/message. The process is illustrated below.
- Cloud Push park credentials established.
- Inactive state detected and client session parked.
- Some state change in the application triggers a priority Ajax Push event.
- ICEpush notification is delivered to the device using the specified cloud connector.
- Notification received at device, and user notification is given.
At some time later the user acknowledges the notification by reactivating the application, causing the ICEpush bridge to reestablish itself, and a page update to occur reflecting the current state of the application.
While there is some relatively complex infrastructure in ICEmobile-Faces to handle cloud push, the programming model is simple, and well-aligned with the standard ICEfaces 2 Ajax Push APIs.
A standard Ajax Push notification is generated using:
A priority push, with option to do a cloud push is generated using:
From the developers perspective, there are no additional considerations beyond supplying the additional PushMessage. Selection of the normal or cloud push transport, as well as selection of the cloud push connector type, is transparent to the developer and handled by the ICEpush core.
The different cloud push connectors all require different server-side infrastructure to operate. The email connector is available in the Open Source distribution, but the proprietary connectors are available only with the Enterprise distribution, and specifically require the ICEpush-ee.jar.
C2DM requires a Google account to act as the sender for C2DM, and that sender must be registered with the C2DM service at Google. You can read more about Google requirements related to C2DM as follows:
Once you have a Google account registered as a sender for C2DM, you can configure your web application either with context parameters in the web.xml,
or with a Java system property at build time.
If the email connector is used, there must be an email client configured on the device to match the email address associated with the client. This email address can either be configured as part of the web application itself,
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or if a device container is use, it can be configured from the container preferences.