Inside a Demo Mobile Application, Part 2
Using Java and JavaFX to create Java client applications that work on mobile devices.
by Johan Vos

In Part 1 of this series, I showed how developers can use the Java APIs (for example, JavaFX APIs) to create a Java client application that runs on desktop, mobile, and embedded devices using Gluon Mobile. I showed that with a 100 percent pure Java codebase, applications can be uploaded to the Apple App Store and the Google Play Store.

The app we created in that article was a standalone application. When the app ran, it didn't need any additional information, apart from what is in the application bundle. It goes without saying, but this is not a very common situation. In reality, most apps interact with back-end applications. Typical back-end interactions include the retrieval of weather information from a REST endpoint or of the financial transaction associated with buying a ticket and making a seat reservation for a concert. Because there are many Java developers working on back-end projects, these back-end systems are often familiar environments.

The example demonstrated in the previous article presented end users with a selection of coffee types from which they could place an order. The list of possible coffee types was statically included inside the application. In this article, we will make this a remote interaction.

Mobile Apps Need Back-End Data and Functionality

We have a back-end system that provides the possible coffee types. By doing a REST call to a specific endpoint, the coffee types are returned in a JSON response:

curl ""

There are a number of ways to connect a mobile app with an enterprise back end and to handle the interactions. In theory, you can directly use the tools that you use in enterprise systems to connect to other enterprise systems. In practice, however, this is not encouraged in most cases due to a number of reasons:

  • Although mobile devices have become more powerful, they still have fewer resources than servers do, and those resources need to be shared with other apps. Enterprise software is often designed with getting maximum performance from available resources in mind, rather than with sharing resources.
  • Mobile devices are not always connected to the internet. Lots of boilerplate code would be needed to check if all requests are successfully retrieved and to optionally reschedule failed requests when connectivity is restored—taking transactional behavior into account.
  • Mobile devices and apps have a specific lifecycle and need to behave according to specific policies. Some resources are conditionally available. The network might be a free Wi-Fi network or a paid cellular network. The battery might be low, and the app might be in the background. Depending on those conditions, an app should behave differently. Those conditions are not found on enterprise systems.
  • Back-end systems typically don't want to allow any client to connect to them. Because mobile users can be connected via any mobile data provider or Wi-Fi network, a direct connection from the mobile app to the back-end system requires the back-end system to be accessible by every potential host on the planet. This increases the chances of attacks and security breaches.

Respecting Mobile and Enterprise Requirements by Using an MBaaS

A typical solution to overcome these problems is to position a mobile back-end as a service (MBaaS) between the mobile devices and the back-end system.

Figure 1. Example MBaaS connecting mobile devices to a back-end system

Using an MBaaS, mobile devices don't connect to the back end directly; instead, they connect to the MBaaS, which may forward their request to a back-end system.

Gluon CloudLink is an MBaaS that can be connected to by mobile apps regardless of the way in which they are written. However, Gluon CloudLink works best when mobile apps are written with Gluon Mobile, the toolkit used to create the app in the previous article.

Gluon CloudLink is a public cloud service that can connect to other back-end and cloud systems (see Figure 2), but you can also install it as a service inside other clouds. In this article, I will demonstrate this using Oracle Container Cloud Service, which is part of Oracle Cloud (see Figure 3).

Figure 2. Gluon CloudLink as a public cloud service
Figure 2. Gluon CloudLink as a public cloud service
Figure 3. Gluon CloudLink as a service inside Oracle Cloud
Figure 3. Gluon CloudLink as a service inside Oracle Cloud

Installing Gluon CloudLink on Oracle Cloud

If you have an Oracle Cloud (trial) account, you can install your own or third-party software in Oracle Container Cloud Service. You can configure a datasource (for example, a MySQL service or an Oracle Database service), and link it to your application(s) in Oracle Container Cloud Service. You can access more Oracle Cloud services, for example, you can leverage the storage capabilities provided by Oracle Storage Cloud Service. A great advantage of Oracle Container Cloud Service is that it supports a microservices architecture, and it allows for scalable applications. Gluon CloudLink is a back-end service that internally contains a number of microservices, and each of them can individually be scaled. Using Gluon CloudLink on Oracle Cloud allows you to scale the middleware according to your own needs. You have your own instance(s) running Gluon CloudLink, which connect to your own database service (the public cloud version of Gluon CloudLink is a multitenant service, where data is isolated between applications, but it is stored in the same data storage system).

Note: In the next article, I will explain the internals of Oracle Container Cloud Service, and I will show how a microservices product such as Gluon CloudLink can be installed and configured on Oracle Cloud. In this article, I will abstract away these internal details to simplify the discussion.

Applications that leverage Gluon CloudLink can be managed using Gluon Dashboard, which is a web application that allows developers, architects, and operators to configure and monitor their mobile apps and the connections to the enterprise back-end systems. You can open Gluon Dashboard by navigating to

Figure 4. Gluon Dashboard welcome page

By default, Gluon Dashboard will connect to the public Gluon CloudLink software as a service (SaaS) installation. Navigate to the Oracle Cloud–specific page at to be able to connect to your privately hosted Gluon CloudLink instance in your Oracle Cloud infrastructure. In case this is the first time you want to use Gluon CloudLink on your Oracle Cloud infrastructure, Gluon Dashboard will guide you through the process of installing Gluon CloudLink on Oracle Cloud. You need to provide your Oracle Cloud credentials, and then the Gluon CloudLink framework will be provisioned on your own Oracle Cloud instances. Your data is stored in an instance of Oracle MySQL Cloud Service that is private to you. If you don’t have an Oracle Cloud account, you can sign up for a trial.

After you successfully authenticate in the Gluon Dashboard, the application will search for an existing Gluon CloudLink installation on your Oracle Cloud environment. If it doesn't find one, a dialog box will be shown proposing to install Gluon CloudLink on your Oracle Cloud environment, as shown in Figure 5:

Figure 5. Dialog box for installing Gluon CloudLink

Click OK if you want to install the software. The required software will be installed on your account, and you can follow the progress in a console. This can take some time (for example, 15 minutes).

Once the Gluon CloudLink microservices are installed on your Oracle Cloud environment, you are redirected to the Gluon Dashboard landing view (Figure 6), which shows a menu and an initially empty usage graph.

Figure 6. Gluon Dashboard landing view

Tunneling Requests Through Gluon CloudLink

There are many things you can do with Gluon Dashboard, but we will focus on getting the coffee types from our back-end system and providing them to the mobile app. If you select API Management, you can add a remote function. Let's create a function named otnCoffees and provide the REST endpoint that will return the coffee types, as shown in Figure 7:

Figure 7. Adding a remote function

When you click Save, Gluon Dashboard sends the information to Gluon CloudLink. Then, when a mobile app requests the otnCoffees function, Gluon CloudLink knows what to do: it will invoke the remotely defined endpoint.

Now, we need to modify the code for the mobile app so that it retrieves the list of coffee types by calling Gluon CloudLink. Currently, we have the service providing the data as follows:

    public ReadOnlyListProperty<OTNCoffee-> retrieveOTNCoffees() {
        ObservableList<OTNCoffee-> list = FXCollections.observableArrayList();
        Platform.runLater(() -> {
            list.add(new OTNCoffee("type1", "Moka"));
            list.add(new OTNCoffee("type2", "Arabica"));
        return new SimpleListProperty(list);

We will now use the Gluon CloudLink client APIs and replace that code with the following code:

    public ReadOnlyListProperty<OTNCoffee> retrieveOTNCoffees() {
        if (otnCoffees == null) {
 DataClient dataClient = DataClientBuilder.create()
            GluonObservableList<OTNCoffee> gluonCoffees = DataProvider.retrieveList(dataClient.createFunctionListDataReader("otnCoffees", OTNCoffee.class));
            otnCoffees = new ReadOnlyListWrapper<>(gluonCoffees);
        return otnCoffees.getReadOnlyProperty();

In this new code, we first construct a Gluon CloudLink DataClient, which will manage the connection with Gluon CloudLink and beyond. The DataClient is asked to operate in CLOUD_FIRST mode, which means that it will first ask Gluon CloudLink for its data, and if a connection cannot be made, it will look into its local cache (on the mobile device) to present the data that was retrieved before.

Next, the DataClient is bound to the remote function named otnCoffees and the result is expected to be a list of OTNCoffee instances.

The static method retrieveList on DataProvider is then called, and the data is stored in a GluonObservableList, which extends the JavaFX ObservableList by adding a few properties that contain information about the status of the retrieval.

Note that we didn't have to provide a URL for the actual back-end service. This is all configured by using Gluon Dashboard in Gluon CloudLink, so once the mobile application can make a secure connection to Gluon CloudLink, we're all set.

Gluon CloudLink defines a key pair for each mobile application, and in the case of a hosted version of Gluon CloudLink (as opposed to the public SaaS version of Gluon CloudLink), the host name needs to be provided to the mobile application as well.

In Gluon Dashboard, the Credentials view allows you to store the required configuration file inside the resource directory of the mobile application, where it will be picked up by the Gluon Mobile tools that create the app.

Figure 8. Credentials view

As can be seen in Figure 8, the required configuration is generated by Gluon CloudLink in a JSON format.

On the client, we simply bind the call to the otnCoffees function, as defined in Gluon CloudLink, to a JavaFX ObservableList. By moving the configuration to the middleware, we avoid any risks related to changes in the URL structure or protocol, which would require a rebuild, redeployment, and redistribution of the mobile app. If you don't want to stress your real back-end system, you can also use Gluon Dashboard to send mock data back to your mobile client. The switch between mock data and the real data can be made by a single click in Gluon Dashboard, rather than by having to recompile and resubmit your app to the App Store and the Play Store.

Note that we didn't create a separate thread for retrieving the data from the back-end system. This is done under the hood by the Gluon CloudLink client. The result is a JavaFX ObservableList that can immediately be used by the graphical components in the client app—in this case, the list is used in a selection control.

In this particular case, the three coffee types are likely to arrive quickly at the mobile app. But in case there is much data to be retrieved from the back end, using the ObservableList allows developers to already render the retrieved data while new data comes in. Because Gluon CloudLink Client will populate the ObservableList when the data is parsed, the visual control that is backed by this ObservableList will be updated on the fly. This eliminates a huge amount of boilerplate code.


In this article, we extended the OTN demo app from the previous article. Rather than showing a hardcoded list of coffee types, we retrieved the list from a back-end service. However, we didn't access that back-end service directly; we used middleware called Gluon CloudLink that bridges the gap between the mobile devices and the enterprise infrastructure.

We explored how you can provision Gluon CloudLink on your Oracle Cloud infrastructure, and how you can easily configure Gluon CloudLink using its dashboard to map client requests onto external requests by defining functions that can be called on the mobile client.


About the Authors
Johan Vos started working with Java in 1995. He was part of the Blackdown team, porting Java to Linux. His main focus is on end-to-end Java, combining back-end systems and mobile/embedded devices. He received a Duke's Choice Award in 2014 for his work on JavaFX on mobile devices.
In 2015, he cofounded Gluon, which allows enterprises to create mobile Java client applications leveraging their existing back-end infrastructure. Gluon received a Duke's Choice Award in 2015. Vos is a Java Champion, a member of the BeJUG steering group and the Devoxx steering group. and he is a JCP member. He is the lead author of Pro JavaFX 8 (Apress, 2014), and he has been a speaker at numerous conferences on Java.
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