Android example using microprofile config

This example shows an Android application implemented in Java using Jetpack Compose for the views, Reactive Extensions for Java and the SmallRye config implementation of microprofile-config for configuration.

Building

Install gradle and gradle wrapper

brew install gradle
gradle wrapper

Download the latest version of Android Studio and open the project. Then create a simulator device and debug it on that device.

Configuration

The app can be configured in the src/main/resources/application.properties file. According to the standard also a META-INF/microprofile-config.properties is present.

Problem with Android missing java.nio.file jar provider

in the ApplicationConfiguration.java we cannot use the usual way to get the config:

var config = ConfigProvider.getConfig().unwrap(SmallRyeConfig.class);

To see the problem remove the comment in the above source code line and try to uses this as a config instead of the current one.

This crashes with a java.nio.file.ProviderNotFoundException propably because the android implementation of java.nio.file contains no jar file provider. For Details see Jar and Zip FileSystemProvider not present on API 26+.

As a workaround we implement our own ConfigSourceProvider.

How to use microprofile config in a new empty Android start project

• Download Android Studio
• Start Android Studio
• create a new Project "Empty Activity"
• Under "Gradle Scripts" open build.gradle.tk (Module :app)
• add the following line to dependencies:

implementation("io.smallrye.config:smallrye-config:3.4.4")

• add the following line excludes += "META-INF/INDEX.LIST" to the same build.gradle.tk so that the section reads:

    packaging {
        resources {
            excludes += "/META-INF/{AL2.0,LGPL2.1}"
            excludes += "META-INF/INDEX.LIST"
        }
    }

• open MainActivity.kt and add the following line after super.onCreate(savedInstanceState):

    val config = ConfigProvider.getConfig().unwrap(SmallRyeConfig::class.java)

• Start the project, it will display "Hello, Android!
• In Project Explorer switch from "Android" to "Project" view
• Navigate to "app/src/main" and add a folder "resources" and below resources add a folder "META-INF"
• Add a file "microprofile-config.properties" to the folder app/src/main/resources/META-INF
• start the project again