Javaでクロスプラットフォームのモバイルアプリを作成する方法

Javaを使用してクロスプラットフォームのモバイルアプリを作成できることをご存知ですか?はい、あなた自身をつまんでください、あなたはそれを最初に正しく読みます!既存のJavaの知識を使用して、AndroidとiOSでパフォーマンスの高いアプリを作成する方法の基本を12の簡単なステップで説明します。これはすべて、GUIツールキットとしてJavaFXを使用して行います。

しかし、最初に、もう少し前景。AndroidとiOSの両方のアプリケーションを構築できるようにするには、後続の要件を満たす必要があります。ただし、iOSアプリケーションを構築したくない場合は、Java SE 8をサポートするx64ビットマシンで自由に開発できます。このプロジェクトは、gradleで構築されたGitリポジトリになります。ただし、Gitリポジトリを作成する必要はありません。

要件は次のとおりです

  • JDK1.8準拠のJVM
  • Androidコマンドラインツール(SDK v.27)
  • XCode 9.2
  • Gradle 4.2
  • Gitラージファイルストレージ(v.2.5.0)(gitリポジトリを作成したくない場合は不要)
  • できれば少なくとも4GRAM

せっかち?最終結果を見たいですか?以下の完成したプロジェクトをチェックしてください。

afinlay5 / OnyxFx

クロスプラットフォーム(Android / iOS / Linux / macOS / Windows)JavaFXアプリレンダリングであるOnyxFxのGradleソースコードリポジトリ… github.com

私の開発環境はFedoraLinux28とmacOSHighSierraです。それが邪魔になったので、掘り下げてみましょう。

1)プロジェクトを格納するフォルダーを作成します

私は自分のプロジェクトOnyxFxを次のようにホストしました:「/ home / adriandavid / Projects / OnyxFx」。もちろん、どこでも自由にプロジェクトを主催できます。

2)gradle、Gitを初期化し、JAVA_HOMEを設定します

プロジェクトディレクトリのルートでターミナルを開きます。gradleが適切に構成されている場合、次のコマンドを実行すると、次のように表示されます。

gradle -v

gradleに、「JVM」というラベルの付いたセクションの隣にJava Development Kit(JDK)8のインストールがリストされていることを確認する必要があります。

これを行うには多くの方法がありますが、最も簡単な方法は、JAVA_HOME環境変数が適切に設定されていることを確認することです。

環境に応じて、これを行うには多くの方法があります。ほとんどの* nixの環境でこれを行う1つの方法は、変数を設定することです/home//.bRCまたは/ etc /プロファイル。ご使用のオペレーティング・システムのマニュアルを参照して、JAVA_HOME環境変数が正しく設定されていることを確認してください。

.bashrcまたはprofileの末尾に次の行を含めて、JAVA_HOMEが正しく設定されていることを確認できます。

JAVA_HOME=/home/adriandavid/java/oracle_jdk1.8.0_181/export JAVA_HOME

注:ここにOracleのJDK8をインストールできます。

次に、次のいずれかのコマンドを実行して、シェルが上記の変更を反映していることを確認します。

source ~/.bashrcsource /etc/profile

次のコマンドを入力して、変数が正しく設定されていることを確認します。

echo $JAVA_HOME

それでも問題が発生する場合、またはMicrosoft Windowsを使用している場合は、こちらを参照してください。

まず、git initプロジェクトのルートディレクトリで実行して、Gitリポジトリを初期化します。注:gitリポジトリをホストしたくない場合は、この手順をスキップできます。

次に、gradle initプロジェクトのルートディレクトリで実行して、gradleリポジトリを初期化します。この手順は必須です。

注:私の例は少し異なって見えることに気付くでしょう。これは、ローカル環境ですでにgradleとGitが初期化されているためです。

3)グルーヴィーに!gradle.buildを編集して

うまくいけば、アース・ウィンド・アンド・ファイアがあなたがグルーヴィーになるのを助けることができます!お気に入りのテキストエディターの電源を入れ、プロジェクトのルートディレクトリにあるbuild.gradleを編集して、その内容を次のGitHubの要点の内容に置き換えます。

These build.gradle settings configure our gradle project to use the javafxmobile plugin, which is the work horse of our project. You can learn more about the plugin here and here. Among many things, the javafxmobile plugin automates the process of downloading (from Maven Central or jcenter) and adding the iOS and Android SDKs to your application’s classpath.

If you are familiar with gradle, maven, or ant, great — you probably have an idea of what’s going on. If you are not familiar with gradle, don’t worry about it. All you need to understand is that gradle is a build tool used to automate many tasks involved in building apps such as: grabbing dependencies, project organization, and so on.

Notice that we are targeting Android 7.1 Nougat (API version 25) and iOS 11 (we will see where this is done shortly). You may adjust these values as you see fit. Note, however, that in the case of Android, you must ensure that the API version matches the version of the SDK that you have download (more on this later).

Lastly, I will not demonstrate the production of signed executables in this tutorial. For this reason, iOSSkipSigning is set to true and we do not make use of the releaseAndroid gradle task. You can, however, provide the appropriate accommodations to produce signed apps.

4) Make a new file called gradle.properties and configure it

Create a new file in the project’s root directory called gradle.properties and add the following content to the file.

robovm.device.name=iPhone-7robovm.sdk.version=11.0org.gradle.jvmargs=-Xms4g -Xmx8g

These settings tell the javafxports plugin to use an iPhone-7 as the on-board emulator, to target iOS 11, and to pass the Xms and Xmx flags to the JVM, which specifies both the initial memory pool to 4GB and the maximum heap memory pool to 8GB. This will be necessary for the compilation of the openJDK and the development of the iOS build.

5) Install Homebrew (iOS only)

If you do not have a Mac and are not intending to produce an iOS build, feel free to skip this step.

Open the terminal in macOS and paste the following command.

/usr/bin/ruby -e "$(curl -fsSL //raw.githubusercontent.com/Homebrew/install/master/install)"

6) Install the USB Multiplexing Socket (iOS only)

Only move on to this step if Homebrew has successfully installed. If you do not have a Mac and are not intending to produce an iOS build, feel free to skip this step.

Open the terminal in macOS and paste the following command.

brew install usbmuxd

7) Grab the Android Command Line Tools

Grab Android Command Line Tools for your platform here. After the download has finished, unzip the folder and paste the contents in the directory of your choice. For me, this was /home//Android.

8) Set Android_HOME, Grab necessary Android packages

As with Java, gradle needs to know where to look to find the Android Command Line Tools. There are a few ways to do this. However, in the spirit of simplicity and consistency, we will set the ANDROID_HOME environmental variable in this tutorial. Add the following variable in the same way that we did it for JAVA_HOME. For example:

ANDROID_HOME=/home/adriandavid/Android/ export ANDROID_HOME

Remember to reload the shell by adding source le> as we did for JAVA_HOME.

Now, grab the tools necessary to build the Android build. Execute the following command:

# *.nix./sdkmanager "platform-tools" "build-tools;25.0.3" "platforms;android-25" "extras;android;m2repository" "extras;google;m2repository"
or
#Windowssdkmanager "platform-tools" "build-tools;25.0.3" "platforms;android-25" "extras;android;m2repository" "extras;google;m2repository"

Take careful notice that the SDK and API version we have specified in gradle.build correspond to the version we have specified in this command. Namely, “25”. Should this be misaligned, the build will not succeed.

9) Create the application’s directory structure

To automate the process of creating these directories, execute the following shell script.

Bourne-Again Shell / Korn Shell:

Windows Shell (cmd):

Save the file as mkpdir.bat or mkpdir.sh and execute the file from the project’s root directory as root (or Administrator).

# *.nixchmod +x mkdir.sh-sh ./mkpdir.sh
# Windowsmkpdir

Notice that we created directories for embedded and desktop. We will produce a desktop build, because it takes no additional work to do so. However, we will not produce any builds for embedded devices.

10) Create your JavaFX Application!

Navigate to /src//java and begin developing your JavaFx application! Application resources are stored in /src//resources.

You can start with a simple Hello World application or look at the source code that I have put together here. OnyxFx is an application I made, following these instructions, that makes REST calls over HTTP to the OnyxFxAPI. The API, in turn, is a web scraper that will return the statistical data (points per game, rebounds per game, assists per game) for the NBA® player and season the client specifies. It returns the data as JSON, which is then parsed and displayed to the screen of the mobile app. Feel free to edit it!

Keep in mind that although you can share source code, you should include custom edits in each copy of the source, should you want to make device specific changes.

Also note that the underlying compiler (MobiDevelop’s fork of RoboVM) does not fully support all Java 8 APIs. If you look very closely at my source code, you will notice that in the iOS version of the source code, I have removed unsupported API such as java.util.function.BiConsumer and java.util.Map.replace().

11) Create a RAM disk for iOS builds (iOS only)

The compilation process for iOS is very resource-heavy, as the plugin will compile the entire openJDK and other libraries twice to create a fat JAR that it will use to build your application. Therefore, you should preemptively create a RAM disk to accommodate for the memory requirements.

This step, however, is subject to your judgement of your machine’s capabilities. For context, the macOS machine that I used to compile my iOS app has 4GB of DDR2 RAM. I decided to make an 8GB RAM disk. To do so, execute the following command in the terminal.

SIZE=8192 ; diskutil erasevolume HFS+ ‘RoboVM RAM Disk’ `hdiutil attach -nomount ram://$((SIZE * 8192))`

12) Build and Run your application!

To build your application, execute the gradle wrapper in the root directory from the terminal as follows.

./gradlew clean build

This will produce a desktop application packaged as a JAR with scripts to run the application provided in /build/distributions/ar>; and /build/distributions/Name.zip>. Should you unzip the directories, you will notice the following structure:

Original text


Notice that in /bin there are scripts to execute the application. These scripts rely on preserving the current folder structure. Also notice that is not necessary for you to have tree installed. It is used here simply for illustrative purposes.

There is, additionally, a standalone JAR that you can use to execute the application on any desktop environment supporting JavaFX 8. To run the application, execute one of the following:

# Navigate to /build/distributions//
#On *.nixcd bin./
#On Windowscd bin
#Platform agnosticjava -jar OnyxFxMobile.jar (or double click, if jvm is configured to run .jar files)
Note: If the executable providing "java" is not the same vendor and/or version of the Java 8 JDK with which you built this application, the jar may not run. JavaFX 8 builds between the openJDK & Oracle JDK are incompatible.
Otherwise: /location/to/java8/bin/java -jar 

View this project’s gradle tasks

You can view this project’s gradle tasks by running the following in the project’s root directory.

./gradlew tasks

To Compile, Run on Desktop

The following command will run your project in the host environment.

./gradlew jar./gradlew run

You will find a standalone jar in build/libs/t;.jar .

To Compile, Run on Android

./android #Generates a debug Android apk containing the JavaFX application.
./androidInstall #Launch the application on a connected android device.
./androidRelease #Generates a release Android apk containing the JavaFX application.
Note: You will need to configure a valid signingConfig when releasing an APK (javafxports).

You will find two APKs in build/javafxports/android.

The first will be named t;.apk.

The second will be named -unaligned.apk.

To Compile, Run on iOS

./createIpa - Generates an iOS ipa containing the JavaFX app.
./launchIOSDevice - Launches app on a connected ios device.
./launchIPadSimulator - Launches app on an iPad simulator.
./launchIPhoneSimulator - Launches app on an iPhone simulator.

You will find three executables in build/javafxports/ios.

The first will be named t;.ipa.

The second will be named ame>.dSYM.

The third will be named <AppName>.app.

Some screenshots of my sample app

On Desktop

On Android

On iPhone

On iPad

Splash Screen

My Closing Thoughts

javafxports is a promising project that aims to bring JavaFX and the Java SE platform onto mobile and other devices. In a way, the tool parallels Xamarin in its efforts. However, the project has a lot of work left to be done.

For a start, the plugin currently does not fully support Java 8. On Android, it uses retrolambda to handle Java 8 Lambda Expressions & Method References. It technically is up to Java 6. Additional dependencies make it such that you can use Java 8. However, the process is straightforward, the builds work as expected, and the compilation time is not too long.

On iOS, however, the builds are extremely memory-intensive and the compilation process takes a very long time. The following is a snippet of the log for ./gradlew createIpa task.

:createIpa (Thread[Task worker for ‘:’,5,main]) completed. Took 1 hrs 46 mins 40.198 secs.

In total, the process consumed about over 6GB of RAM on my machine. This is hardly ideal. However, the future is promising. A company called Gluon has developed a high performance, fully modular custom JVM fully supporting Java 9, that you can read more about here.

This article is originally published on the blog section of my homepage, here.

Resources to explore:

  • JavaFxMobile Plugin Git Repo: //github.com/javafxports/javafxmobile-plugin
  • JavaFxPorts Documentation: //docs.gluonhq.com/javafxports/#_how_it_works
  • JavaFxPorts Homepage: //javafxports.org/
  • Gluon Documentation: //gluonhq.com/developers/documentation/
  • Google Groups Page for JavaFxPorts: //groups.google.com/forum/#!forum/javafxports
  • StackOverflow Page for JavaFxPorts: //stackoverflow.com/questions/tagged/javafxports
  • Gluon Mobile Pricing/License Options: //gluonhq.com/products/mobile/buy/