Welcome!

Java IoT Authors: Pat Romanski, Elizabeth White, Liz McMillan, Yeshim Deniz, Frank Lupo

Related Topics: Java IoT, Recurring Revenue

Java IoT: Blog Feed Post

The Magic Sauce for Multi-Browser-Tab Support in JDeveloper ADF Apps

PageFlowScope with Unbounded Task Flows

Within JDev 11g+ experienced ADF programmers will be familiar with PageFlowScope beans used by tasks flows, in particular Bounded Task Flows (BTFs) where they provide the equivalent of session scope for variables for the life of the BTF for a specific user session. Indeed the Oracle documentation says the following about PageFlowScope beans:

Choose this scope if you want the managed bean to be accessible across the activities within a task flow. A managed bean that has a pageFlow scope shares state with pages from the task flow that access it. A managed bean that has a pageFlow scope exists for the life span of the task flow

Source: Oracle Fusion Dev Guide 11.2.1 Section 18.2.4 What You May Need to Know About Memory Scope for Task Flows

Given we know BTFs have a distinct beginning and end for each user session, a "life span" as such, and conversely Unbounded Task Flows (UTFs) live for the life of the application which is nearly forever, it would appear that PageFlowScope beans only apply to BTFs. However PageFlowScope beans provide some magic sauce with UTFs that shouldn't be ignored. Before we can have a look at this magic sauce we need to cover some background on modern browsers.

Multi-tab browsers and the challenge for web applications
Readers will be familiar that over the last several years browsers have increased in sophistication, providing users with more and more features. One such feature is that of tabs, more commonly referred to as multi-tab browsing. Back in the dim dark ages of the Internet (circa 2005?) if users wanted to surf more than one website at a time they needed to open multiple instances of their browser. Typically each browser instance took out a single connection and server-side session (assuming a stateful application) with whichever server they were visiting. If the user had multiple instances open to the same website this resulted in the same amount of connections and sessions.

At some point in time web browsers introduced the support for tabs, allowing within the one browser instance the user to surf multiple websites in separate tabs. I'll take a guess and say the browser authors when introducing this feature had a careful think about how users visit websites, and they realized users when searching for information on websites might spawn several tabs all visiting the same website but each tab viewing different pages within that single website.

So browsers introduced a feature set to give users the ability to search for information even faster, yet the browser vendors also recognized an issue. Potentially users were now relatively free to spawn lots of tabs (and if you're like some users you keep on spawning tabs, never closing any, until you shut down the browser). If the old regime of a connection per tab was followed at the client (browser) side, and a session per connection at the server (website) side, computing resources would be strained.

How to fix? Simple really, per website on the browser side, regardless the number of tabs open to a website via a browser, it should share the connections across the tabs. Result? Instant resource saving on the client. In turn on the server side as there isn't any default way to identify the different tabs as their separate requests hit the server through the same connection, the server too need only store 1 session.

Today from the users' perspective (at least the tech savvy users) multi-browser tabs is an expected feature and one when not available for whatever reason causes frustration either with the browser or the website they are using. This implies any web application we build really needs to support (or at least not hinder) this functionality.

What's this got to do with ADF?
The question is probably rhetorical for readers at this point, but what's this got to with ADF?

Traditionally JavaServer Faces (JSF) programmers and ADF programmers have been taught if you want to maintain state (variables) for the life of a user's session you put it in a SessionScope bean. Examples of such variables include the time the user first accessed the system, the customer ID of the current customer that the user is working with on the phone, or the items in a shopping cart. Definitely these should go in SessionScope.

Or should they?

With modern browsers what should happen with these variables when the user spawns two tabs to our application sharing the same connection/session? Looking at our previous examples it's easy to agree the time the user first accessed the system would be one and the same across both tabs. But what about our other examples?

For our customer ID example, reasonably in some applications you might want two different tabs to show two different pages for information on the same customer, so SessionScope seems reasonable enough. But alternatively imagine you're a call centre operator, taking a call from one customer while finishing recording data about the previous customer. It would be mighty handy to have two browser tabs to do this. As a result the separate tabs really require their own SessionScope customer ID. How to do that?

The question gets murkier when considering shopping carts. For an Amazon user having two separate carts on two separate browser tabs would seem undesirable. But let's take another call centre example where an operator is taking a phone call from a customer wanting to place two separate orders. Things get tricky if the customer is moving items between the orders, so different tabs supporting different orders could be desirable. Again the vanilla SessionScope bean won't solve this.

So we can see sometimes depending on the needs of the application, we need to provision session state for separate browser tabs. At the moment JSF1.X/2.0 has no inbuilt solution for this problem (there's been much discussion about including a new ConversationScope bean in the past), but as you can probably guess a PageFlowScope at the UTF level in ADF solves this problem. For every browser tab opening a page in the UTF that references a managed PageFlowScope bean a separate instance of the bean will be created.

The hint of the secret life of the PageFlowScope is revealed in Section 5.7 Passing Values Between Pages of the JDev Web Guide 11.1.2 where it states:

The ADF Faces pageFlowScope scope makes it easier to pass values from one page to another, thus enabling you to develop master-detail pages more easily. Values added to the pageFlowScope scope automatically continue to be available as the user navigates from one page to another, even if you use a redirect directive. But unlike session scope, these values are visible only in the current page flow or process. If the user opens a new window and starts navigating, that series of windows will have its own process. Values stored in each window remain independent.

Specifically note the last 2 sentences.

How does ADF technically solve identifying the separate tabs?

Earlier on we mentioned from the server's point of view, because multi-browser tabs share the same connection with the server, by default the server has no inherit mechanism to differentiate the separate browser tabs and therefore no mechanism to know when to spawn separate PageFlowScope beans. So how does ADF actually technically solve identifying the separate tabs?

Imagine you've created an ADF application to lodge infringements. Some infringements take seconds to fill out and complete, others take time to gather the data, requiring multiple tabs to enter more than one infringement at a time.

For such an ADF application we could serve the service via a link on our portal such as:

http://www.wewantyourmoney.com/infringements/ticket

In this case ticket represents a JSPX file in our UTF of our application.

On accessing the URL for the first time regular ADF users will know the server in responding with the required page will also replace the URL with something like the following:

http://www.wewantyourmoney.com/infringements/ticket?_adf.ctrl-state=p1zu...

This parameter and its value is also buried in the HTML source to be used on the next request. Also inside the page source is a form parameter Adf-Window-Id with a unique value given by the server.

When the page is submitted along with the hidden _adf.ctrl-state and Adf-Window-Id parameter gained from the previous server response, this gives ADF a mechanism for tracking the current session and current page instance.

(Side note: Behind the scenes the server is smart enough to check the session parameters against the previous known connection/session to stop intruders impersonating another user's session ... you can test this by intercepting the next request before it goes out and changing the _adf.ctrl-state parameter before it hits the server. ADF will complain displaying the following error message "ADFC-12000: State ID in request is invalid for the current session.")

If the server receives another request for the same "naked" URL from the same connection/session, ADF simply assumes a new tab instance, spawns a separate PageFlowScope bean instance, and returns separate _adf.ctrl-state and Adf-Window-Id values in the response. Any subsequent requests to the server from separate multiple tabs for the same user connection are therefore easily separated and the correct PageFlowScope bean instance used.

Alternatively if the user tries to trick the server by copying the URL from another tab with the _adf.ctrl-state variable in the URL, but obviously missing a payload containing the _adf.ctrl-state form parameter and the Adf-Window-Id parameter, again ADF is smart enough to detect this as a new browser tab and spawns a new PageFlowScope bean. This piece of logic is important because it's possible for users to bookmark the current page's URL with the URL parameter, and attempt to come back to it after a spawning a new tab. As such we wouldn't want ADF to be tricked by this simple common use case into thinking the user is in the same original tab when in fact they're launching the application from an old bookmark.

Finally it should be noted if the user session times out or logs out, the PageFlowScope bean will fall out of scope and any reference to the PageFlowScope there after will result in new instance of the bean created.


Demonstration

The following link provides a small demo application from JDev 11.1.2. To set this application up you need to:

a) unzip it and open it in JDev
b) in your integrated WLS server create a user account which you will use to log in to the application

The application is comprised of 4 pages:

a) an unauthenticated Splash page to start the application
b) 2 separate authenticated pages named FirstPage and SecondPage that will demonstrate the bean scopes during an authenticated session
c) an unauthenticated ExitPage which will be called when the user logs out of SecondPage

From here run the Splash.jsf page. Your browser will eventually open with the following URL:

http://localhost:7101/MultiBrowserTabExample/faces/Splash

Select the Go First Page button, at the login enter your credentials, upon which you'll see First Page:

The two fields have default values gathered from two separate beans, one a SessionScope bean and the other a PageFlowScope bean. Note in the JDev log window you'll see log entries from the constructors of both beans, implying they were just instantiated to show the values on the page, and thus why the default values are shown.

Selecting the Go Second Page button takes us to the Second Page where we have the option to change the values:

As example lets change the value for the SessionScope to Alpha and the PageFlowScope value to Beta:

On returning to the first page through the associated button we see that Alpha and Beta values have been successfully carried across requests

Now open a new browser tab to original Splash page using the following URL:

http://localhost:7101/MultiBrowserTabExample/faces/Splash

Diagrammatically to show this, what I've done in the following set of pictures is put the original tab to the left of the image, and the new tab to the right of the image so I could show both tabs at the same time. As such we now have:

In the second tab if we then select the Go First Page button we bypass the login screen automatically as the user is already logged in, and we arrive on the SecondPage as follows:

In the JDev log window we see a new instance of the PageFlowScope bean has been created, but not the SessionScope bean. This backs up what is shown in the new second tab because we can see that the SessionScope value is shared across both tabs, but the PageFlowScope value isn't and we've reverted to the default value (provided through the new PageFlowScope instance).

From here in the second tab we can navigate to the Second Page and update the values of the SessionScope and PageFlowScope beans to Charlie and Delta respectively:

In the second tab if we then return to the FirstPage we see that it maintains the Charlie and Delta values:

...and more importantly in the first tab if we then navigate to the Second Page we see:

In this picture we can see that the SessionScope Charlie value has been shared across both tabs, but the first tab has retained it's original Beta values for it's PageFlowScope bean, showing that the PageFlowScopes are indeed separate across browser tabs.

To conclude the examples, if in the first tab we select the Logout button we automatically move to the ExitPage and we see:

This shows both the SessionScope and PageFlowScope bean resetting back to the original values. The JDev log window also logs the constructor calls of both beans verifying that the old beans have been completed and 2 new instances created.

Finally if we return to the second tab that is still sitting on the First Page, any action results in ADF throwing an exception "java.lang.IllegalStateException: No window for windowId:w2". To be honest I expected an error here because the user behind the scenes has logged out, but this error message looks less than useful. Presumably we need to take care of this specific error in some manner, probably with a task flow Exception handler, but is beyond the scope of this post.

Not all things are born equal - final note on SessionScope vs PageFlowScope

Don't get confused on the use of SessionScope and PageFlowScope beans. Not everything you would have traditionally put in SessionScope need now go in a UTF PageFlowScope bean. How many frequent flyer miles the user has left, the user's preferences and their birthday are good candidates for SessionScope. But if across tabs you will allow the user to test separate values for projecting sales figures, a counter for the numbers of steps completed in submitting separate expense reports or even the tiles placed in a game of tic tac toe, PageFlowScope will be more appropriate.

Read the original blog entry...

More Stories By Chris Muir

Chris Muir, an Oracle ACE Director, senior developer and trainer, and frequent blogger at http://one-size-doesnt-fit-all.blogspot.com, has been hacking away as an Oracle consultant with Australia's SAGE Computing Services for too many years. Taking a pragmatic approach to all things Oracle, Chris has more recently earned battle scars with JDeveloper, Apex, OID and web services, and has some very old war-wounds from a dark and dim past with Forms, Reports and even Designer 100% generation. He is a frequent presenter and contributor to the local Australian Oracle User Group scene, as well as a contributor to international user group magazines such as the IOUG and UKOUG.

@ThingsExpo Stories
Join IBM November 1 at 21st Cloud Expo at the Santa Clara Convention Center in Santa Clara, CA, and learn how IBM Watson can bring cognitive services and AI to intelligent, unmanned systems. Cognitive analysis impacts today’s systems with unparalleled ability that were previously available only to manned, back-end operations. Thanks to cloud processing, IBM Watson can bring cognitive services and AI to intelligent, unmanned systems. Imagine a robot vacuum that becomes your personal assistant tha...
SYS-CON Events announced today that TidalScale will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. TidalScale is the leading provider of Software-Defined Servers that bring flexibility to modern data centers by right-sizing servers on the fly to fit any data set or workload. TidalScale’s award-winning inverse hypervisor technology combines multiple commodity servers (including their ass...
As hybrid cloud becomes the de-facto standard mode of operation for most enterprises, new challenges arise on how to efficiently and economically share data across environments. In his session at 21st Cloud Expo, Dr. Allon Cohen, VP of Product at Elastifile, will explore new techniques and best practices that help enterprise IT benefit from the advantages of hybrid cloud environments by enabling data availability for both legacy enterprise and cloud-native mission critical applications. By rev...
Infoblox delivers Actionable Network Intelligence to enterprise, government, and service provider customers around the world. They are the industry leader in DNS, DHCP, and IP address management, the category known as DDI. We empower thousands of organizations to control and secure their networks from the core-enabling them to increase efficiency and visibility, improve customer service, and meet compliance requirements.
With major technology companies and startups seriously embracing Cloud strategies, now is the perfect time to attend 21st Cloud Expo October 31 - November 2, 2017, at the Santa Clara Convention Center, CA, and June 12-14, 2018, at the Javits Center in New York City, NY, and learn what is going on, contribute to the discussions, and ensure that your enterprise is on the right path to Digital Transformation.
SYS-CON Events announced today that N3N will exhibit at SYS-CON's @ThingsExpo, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. N3N’s solutions increase the effectiveness of operations and control centers, increase the value of IoT investments, and facilitate real-time operational decision making. N3N enables operations teams with a four dimensional digital “big board” that consolidates real-time live video feeds alongside IoT sensor data a...
Amazon is pursuing new markets and disrupting industries at an incredible pace. Almost every industry seems to be in its crosshairs. Companies and industries that once thought they were safe are now worried about being “Amazoned.”. The new watch word should be “Be afraid. Be very afraid.” In his session 21st Cloud Expo, Chris Kocher, a co-founder of Grey Heron, will address questions such as: What new areas is Amazon disrupting? How are they doing this? Where are they likely to go? What are th...
In his Opening Keynote at 21st Cloud Expo, John Considine, General Manager of IBM Cloud Infrastructure, will lead you through the exciting evolution of the cloud. He'll look at this major disruption from the perspective of technology, business models, and what this means for enterprises of all sizes. John Considine is General Manager of Cloud Infrastructure Services at IBM. In that role he is responsible for leading IBM’s public cloud infrastructure including strategy, development, and offering ...
Digital transformation is changing the face of business. The IDC predicts that enterprises will commit to a massive new scale of digital transformation, to stake out leadership positions in the "digital transformation economy." Accordingly, attendees at the upcoming Cloud Expo | @ThingsExpo at the Santa Clara Convention Center in Santa Clara, CA, Oct 31-Nov 2, will find fresh new content in a new track called Enterprise Cloud & Digital Transformation.
SYS-CON Events announced today that NetApp has been named “Bronze Sponsor” of SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. NetApp is the data authority for hybrid cloud. NetApp provides a full range of hybrid cloud data services that simplify management of applications and data across cloud and on-premises environments to accelerate digital transformation. Together with their partners, NetApp emp...
Smart cities have the potential to change our lives at so many levels for citizens: less pollution, reduced parking obstacles, better health, education and more energy savings. Real-time data streaming and the Internet of Things (IoT) possess the power to turn this vision into a reality. However, most organizations today are building their data infrastructure to focus solely on addressing immediate business needs vs. a platform capable of quickly adapting emerging technologies to address future ...
Most technology leaders, contemporary and from the hardware era, are reshaping their businesses to do software. They hope to capture value from emerging technologies such as IoT, SDN, and AI. Ultimately, irrespective of the vertical, it is about deriving value from independent software applications participating in an ecosystem as one comprehensive solution. In his session at @ThingsExpo, Kausik Sridhar, founder and CTO of Pulzze Systems, will discuss how given the magnitude of today's applicati...
As popularity of the smart home is growing and continues to go mainstream, technological factors play a greater role. The IoT protocol houses the interoperability battery consumption, security, and configuration of a smart home device, and it can be difficult for companies to choose the right kind for their product. For both DIY and professionally installed smart homes, developers need to consider each of these elements for their product to be successful in the market and current smart homes.
SYS-CON Events announced today that Avere Systems, a leading provider of enterprise storage for the hybrid cloud, will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Avere delivers a more modern architectural approach to storage that doesn't require the overprovisioning of storage capacity to achieve performance, overspending on expensive storage media for inactive data or the overbui...
Widespread fragmentation is stalling the growth of the IIoT and making it difficult for partners to work together. The number of software platforms, apps, hardware and connectivity standards is creating paralysis among businesses that are afraid of being locked into a solution. EdgeX Foundry is unifying the community around a common IoT edge framework and an ecosystem of interoperable components.
SYS-CON Events announced today that Avere Systems, a leading provider of hybrid cloud enablement solutions, will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Avere Systems was created by file systems experts determined to reinvent storage by changing the way enterprises thought about and bought storage resources. With decades of experience behind the company’s founders, Avere got its ...
High-velocity engineering teams are applying not only continuous delivery processes, but also lessons in experimentation from established leaders like Amazon, Netflix, and Facebook. These companies have made experimentation a foundation for their release processes, allowing them to try out major feature releases and redesigns within smaller groups before making them broadly available. In his session at 21st Cloud Expo, Brian Lucas, Senior Staff Engineer at Optimizely, will discuss how by using...
In this strange new world where more and more power is drawn from business technology, companies are effectively straddling two paths on the road to innovation and transformation into digital enterprises. The first path is the heritage trail – with “legacy” technology forming the background. Here, extant technologies are transformed by core IT teams to provide more API-driven approaches. Legacy systems can restrict companies that are transitioning into digital enterprises. To truly become a lead...
SYS-CON Events announced today that CAST Software will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. CAST was founded more than 25 years ago to make the invisible visible. Built around the idea that even the best analytics on the market still leave blind spots for technical teams looking to deliver better software and prevent outages, CAST provides the software intelligence that matter ...
SYS-CON Events announced today that Daiya Industry will exhibit at the Japanese Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Ruby Development Inc. builds new services in short period of time and provides a continuous support of those services based on Ruby on Rails. For more information, please visit https://github.com/RubyDevInc.