Manually Build an Android Hello World Project

Android development is possible without using Gradle. You don't need to depend on it as it is a heavy bloat requires internet connection and downloads a ton of other dependencies, etc. You build faster and know what is going on.

First, you need to install java, in my case, I install the headless version because I don’t use graphics (only command line):

sudo apt-get install openjdk-8-jdk-headless

Then download the last SDK tools of Android

wget https://dl.google.com/android/repository/sdk-tools-linux-3859397.zip
mkdir -p /opt/android-sdk
unzip sdk-tools-linux-3859397.zip -d /opt/android-sdk

Now, we have to install platform tools (which contain ADB), an Android API and build tools. In fact, if you are on Debian, you can avoid installing platform-tools package and only install ADB like that:

sudo apt-get install adb

In this example, I want to compile a simple HelloWorld.

mkdir HelloAndroid
cd HelloAndroid
mkdir -p src/com/example/helloandroid
mkdir obj
mkdir bin
mkdir -p res/layout
mkdir res/values
mkdir res/drawable
mkdir libs

Make the file src/com/example/helloandroid/MainActivity.java and put that inside:

package com.example.helloandroid;

import android.app.Activity;
import android.os.Bundle;

public class MainActivity extends Activity {
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
   }
}

Make the strings.xml file in the res/values folder. It contains all the text that your application uses:

<resources>
   <string name="app_name">A Hello Android</string>
   <string name="hello_msg">Hello Android!</string>
   <string name="menu_settings">Settings</string>
   <string name="title_activity_main">MainActivity</string>
</resources>

The activity_main.xml is a layout file which have to be in res/layout:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent" >
   
   <TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerHorizontal="true"
      android:layout_centerVertical="true"
      android:text="@string/hello_msg"
      tools:context=".MainActivity" />
</RelativeLayout>

You also have to add the file AndroidManifest.xml at the root:

<?xml version='1.0'?>
<manifest xmlns:a='http://schemas.android.com/apk/res/android' package='com.example.helloandroid' a:versionCode='0' a:versionName='0'>
    <application a:label='A Hello Android'>
        <activity a:name='com.example.helloandroid.MainActivity'>
             <intent-filter>
                <category a:name='android.intent.category.LAUNCHER'/>
                <action a:name='android.intent.action.MAIN'/>
             </intent-filter>
        </activity>
    </application>
</manifest>

Build the code

export PROJ=path/to/HelloAndroid

First, we need generate the R.java file which is necessary for our code:

cd /opt/android-sdk/build-tools/26.0.1/
./aapt package -f -m -J $PROJ/src -M $PROJ/AndroidManifest.xml -S $PROJ/res -I /opt/android-sdk/platforms/android-19/android.jar

-m instructs aapt to create directories under the location specified by -J -J specifies where the output goes. Saying -J src will create a file like src/com/example/helloandroid/R.java -S specifies where is the res directory with the drawables, layouts, etc. -I tells aapt where the android.jar is. You can find yours in a location like android-sdk/platforms/android-/android.jar

Now, we have to compile the .java files:

cd /path/to/AndroidHello
javac -d obj -classpath src -bootclasspath /opt/android-sdk/platforms/android-19/android.jar src/com/example/helloandroid/*.java

If you have use an external, add it the classpath:

javac -d obj -classpath "src:libs/<your-lib>.jar" -bootclasspath /opt/android-sdk/platforms/android-19/android.jar src/com/example/helloandroid/*.java

The compiled .class files are in obj folder, but Android can’t read them. We have to translate them in a file called “classes.dex” which will be read by the dalvik Android runtime:

cd /opt/android-sdk/build-tools/26.0.1/
./dx --dex --output=$PROJ/bin/classes.dex $PROJ/obj

But if you use external libraries, do rather:

./dx --dex --output=$PROJ/bin/classes.dex $PROJ/*.jar $PROJ/obj

If you have the error UNEXPECTED TOP-LEVEL EXCEPTION, it can be because you use old build tools and DX try to translate java 1.7 rather than 1.8. To solve the problem, you have to specify 1.7 java version in the previous javac command:

cd /path/to/AndroidHello
javac -d obj -source 1.7 -target 1.7 -classpath src -bootclasspath /opt/android-sdk/platforms/android-19/android.jar src/com/example/helloandroid/*.java

The -source option specify the java version of your source files. Note that we can use previous versions of Java even we use OpenJDK 8 (or 1.8).

We can now put everything in an APK:

./aapt package -f -m -F $PROJ/bin/hello.unaligned.apk -M $PROJ/AndroidManifest.xml -S $PROJ/res -I /opt/android-sdk/platforms/android-19/android.jar
cp $PROJ/bin/classes.dex .
./aapt add $PROJ/bin/hello.unaligned.apk classes.dex

Be aware: until now, we used three AAPT commands, the first and the second one are similar but they don’t do the same. You have to copy the classes.dex file at the root of project like above! Otherwise, AAPT won’t put this file at right place in the APK archive (because an APK is like a .zip file). The generated package can’t be installed by Android because it’s unaligned and unsigned. If you want, you can check the content of the package like this:

./aapt list $PROJ/bin/hello.unaligned.apk

Sign the package

keytool -genkeypair -validity 365 -keystore mykey.keystore -keyalg RSA -keysize 2048

Just answer the questions and put a password.

You can sign an APK like this:

./apksigner sign --ks mykey.keystore $PROJ/bin/hello.apk

Align the package

./zipalign -f 4 $PROJ/bin/hello.unaligned.apk $PROJ/bin/hello.apk

Alignment increase the performance of the application and may reduce memory use.

Test the application

adb install $PROJ/bin/hello.apk
adb shell am start -n com.example.helloandroid/.MainActivity

sh script version

#!/bin/bash

set -e

AAPT="/path/to/android-sdk/build-tools/23.0.3/aapt"
DX="/path/to/android-sdk/build-tools/23.0.3/dx"
ZIPALIGN="/path/to/android-sdk/build-tools/23.0.3/zipalign"
APKSIGNER="/path/to/android-sdk/build-tools/26.0.1/apksigner" # /!\ version 26
PLATFORM="/path/to/android-sdk/platforms/android-19/android.jar"

echo "Cleaning..."
rm -rf obj/*
rm -rf src/com/example/helloandroid/R.java

echo "Generating R.java file..."
$AAPT package -f -m -J src -M AndroidManifest.xml -S res -I $PLATFORM

echo "Compiling..."
javac -d obj -classpath src -bootclasspath $PLATFORM -source 1.7 -target 1.7 src/com/example/helloandroid/MainActivity.java
javac -d obj -classpath src -bootclasspath $PLATFORM -source 1.7 -target 1.7 src/com/example/helloandroid/R.java

echo "Translating in Dalvik bytecode..."
$DX --dex --output=classes.dex obj

echo "Making APK..."
$AAPT package -f -m -F bin/hello.unaligned.apk -M AndroidManifest.xml -S res -I $PLATFORM
$AAPT add bin/hello.unaligned.apk classes.dex

echo "Aligning and signing APK..."
$APKSIGNER sign --ks mykey.keystore bin/hello.unaligned.apk
$ZIPALIGN -f 4 bin/hello.unaligned.apk bin/hello.apk

if [ "$1" == "test" ]; then
	echo "Launching..."
	adb install -r bin/hello.apk
	adb shell am start -n com.example.helloandroid/.MainActivity
fi

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