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I a beginner when it comes to development for Android and I am trying to understand JavaCPP. I want to execute a C++ function from Java inside an Android application. In my example I just use a simple TextView widget that prints what I receive from C++.
Following the documentation, inside the app's build.gradle I have included my javacpp library dependencies
dependencies {
implementation 'org.bytedeco:javacpp:1.5.4'
}
in order to use it in my app. I am testing inside a Native C++ Android Studio template project.
I have uploaded the full project on GitHub for reference: https://github.com/jacobkrieg10/javacppnewexample
And also, down are the relevant files in the project that I think need attention:
NativeLibrary.java:
package com.example.javacplusplus;
import org.bytedeco.javacpp.*;
import org.bytedeco.javacpp.annotation.*;
@Platform(include="NativeLibrary.h")
@Namespace("NativeLibrary")
public class NativeLibrary {
public static class NativeClass extends Pointer {
static { Loader.load(); }
public NativeClass() { allocate(); }
private native void allocate();
// to call the getter and setter functions
public native @StdString String get_property();
public native void set_property(String property);
// to access the member variable directly
public native @StdString String property();
public native void property(String property);
}
}
NativeLibrary.h:
#ifndef NATIVELIBRARY_H
#define NATIVELIBRARY_H
#include <string>
namespace NativeLibrary {
class NativeClass {
public:
const std::string& get_property();
void set_property(const std::string& property);
std::string property;
};
}
#endif // NATIVELIBRARY_H
NativeLibrary.cpp:
#include "NativeLibrary.h"
namespace NativeLibrary {
const std::string& NativeClass::get_property() { return property; }
void NativeClass::set_property(const std::string& property) { this->property = property; }
} // namespace NativeLibrary
CMakeLists.txt:
cmake_minimum_required(VERSION 3.4.1)
add_library(
native-lib
SHARED
NativeLibrary.cpp
native-lib.cpp)
find_library(
log-lib
log)
target_link_libraries(
native-lib
${log-lib})
Note that native-lib.cpp is just the C++ file used in the template, I am ignoring it for now.
build.gradle (corresponding to the app module):
apply plugin: 'com.android.application'
android {
compileSdkVersion 29
buildToolsVersion "29.0.3"
defaultConfig {
applicationId "com.example.javacplusplus"
minSdkVersion 28
targetSdkVersion 29
versionCode 1
versionName "1.0"
testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
externalNativeBuild {
cmake {
cppFlags ""
}
}
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
}
}
externalNativeBuild {
cmake {
path "src/main/cpp/CMakeLists.txt"
version "3.10.2"
}
}
}
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'androidx.appcompat:appcompat:1.2.0'
implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
implementation 'org.bytedeco:javacpp:1.5.4'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'androidx.test:runner:1.3.0'
androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
}
MainActivity.java:
package com.example.javacplusplus;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
// Used to load the 'native-lib' library on application startup.
static {
System.loadLibrary("native-lib");
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Pointer objects allocated in Java get deallocated once they become unreachable,
// but C++ destructors can still be called in a timely fashion with Pointer.deallocate()
NativeLibrary.NativeClass l = new NativeLibrary.NativeClass();
l.set_property("Hello World!");
// Example of a call to a native method
TextView tv = findViewById(R.id.sample_text);
tv.setText(l.property());
// tv.setText(stringFromJNI());
}
/**
* A native method that is implemented by the 'native-lib' native library,
* which is packaged with this application.
*/
public native String stringFromJNI();
}
The application builds fine, but it crashes at runtime inside NativeLibrary.NativeClass l = new NativeLibrary.NativeClass();, with the message couldn't find "libjniNativeLibrary.so" this is my crash log:
--------- beginning of crash
2020-11-16 00:57:38.557 13506-13506/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.javacppapp, PID: 13506
java.lang.UnsatisfiedLinkError: dalvik.system.PathClassLoader[DexPathList[[zip file "/data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/base.apk", zip file "/data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_dependencies_apk.apk", zip file "/data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_resources_apk.apk", zip file "/data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_0_apk.apk", zip file "/data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_1_apk.apk", zip file "/data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_2_apk.apk", zip file "/data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_3_apk.apk", zip file "/data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_4_apk.apk", zip file "/data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_5_apk.apk", zip file "/data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_6_apk.apk", zip file "/data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_7_apk.apk", zip file "/data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_8_apk.apk", zip file "/data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_9_apk.apk"],nativeLibraryDirectories=[/data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/lib/x86, /data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/base.apk!/lib/x86, /data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_dependencies_apk.apk!/lib/x86, /data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_resources_apk.apk!/lib/x86, /data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_0_apk.apk!/lib/x86, /data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_1_apk.apk!/lib/x86, /data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_2_apk.apk!/lib/x86, /data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_3_apk.apk!/lib/x86, /data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_4_apk.apk!/lib/x86, /data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_5_apk.apk!/lib/x86, /data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_6_apk.apk!/lib/x86, /data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_7_apk.apk!/lib/x86, /data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_8_apk.apk!/lib/x86, /data/app/com.example.javacppapp-8V-wRac6X4RLpYvvYEmtGQ==/split_lib_slice_9_apk.apk!/lib/x86, /system/lib]]] couldn't find "libjniNativeLibrary.so"
at java.lang.Runtime.loadLibrary0(Runtime.java:1012)
at java.lang.System.loadLibrary(System.java:1669)
at org.bytedeco.javacpp.Loader.loadLibrary(Loader.java:1683)
at org.bytedeco.javacpp.Loader.load(Loader.java:1300)
at org.bytedeco.javacpp.Loader.load(Loader.java:1123)
at com.example.javacppapp.NativeLibrary$NativeClass.<clinit>(NativeLibrary.java:10)
at com.example.javacppapp.MainActivity.onCreate(MainActivity.java:22)
at android.app.Activity.performCreate(Activity.java:7136)
at android.app.Activity.performCreate(Activity.java:7127)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
2020-11-16 00:57:38.557 13506-13506/? E/AndroidRuntime: at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Note that the example is working when I execute it on desktop x64. So, e.g., using the following NativeLibrary.java file:
import org.bytedeco.javacpp.*;
import org.bytedeco.javacpp.annotation.*;
@Platform(include="NativeLibrary.h")
@Namespace("NativeLibrary")
public class NativeLibrary {
public static class NativeClass extends Pointer {
static { Loader.load(); }
public NativeClass() { allocate(); }
private native void allocate();
// to call the getter and setter functions
public native @StdString String get_property();
public native void set_property(String property);
// to access the member variable directly
public native @StdString String property();
public native void property(String property);
}
public static void main(String[] args) {
// Pointer objects allocated in Java get deallocated once they become unreachable,
// but C++ destructors can still be called in a timely fashion with Pointer.deallocate()
NativeClass l = new NativeClass();
l.set_property("Hello World!");
System.out.println(l.property());
}
}
the output of
$ javac -cp javacpp.jar NativeLibrary.java
$ java -jar javacpp.jar NativeLibrary
$ java -cp javacpp.jar NativeLibrary
$ Hello World!
is Hello World! so it works fine. But I don't know why it doesn't work inside an Android app.
Can anybody help me with this? Does anybody know why it couldn't find libjniNativeLibrary.so? Is there something I need to add in order to complete the setup? Perhaps libjniNativeLibrary.so needs to be generated somehow?
I have added the Build Plugin and the Platform Plugin to the project's build.gradle file; this is how it looks like now:
// Top-level build file where you can add configuration options common to all sub-projects/modules.
buildscript {
repositories {
google()
jcenter()
}
dependencies {
classpath "com.android.tools.build:gradle:4.1.1"
// NOTE: Do not place your application dependencies here; they belong
// in the individual module build.gradle files
}
}
plugins {
id 'java-library'
id 'java-gradle-plugin'
id 'org.bytedeco.gradle-javacpp-build' version "$javacppVersion"
id 'org.bytedeco.gradle-javacpp-platform' version "$javacppVersion"
}
ext {
javacppPlatform = 'android-arm64' // or any other platform, defaults to Loader.getPlatform()
}
dependencies {
implementation gradleApi()
api "org.bytedeco:javacpp:$javacppVersion"
}
allprojects {
repositories {
google()
jcenter()
}
}
// Note: Had to comment this as I was getting the error > Cannot add task 'clean' as a task with that name already exists.
//task clean(type: Delete) {
// delete rootProject.buildDir
//}
tasks.withType(org.bytedeco.gradle.javacpp.BuildTask) {
// set here default values for all build tasks below, typically just includePath and linkPath,
// but also properties to set the path to the NDK and its compiler in the case of Android
}
javacppBuildCommand {
// typically set here the buildCommand to the script that fills up includePath and linkPath
}
javacppBuildParser {
// typically set here the classOrPackageNames to class names implementing InfoMap
}
javacppBuildCompiler {
// typically set here boolean flags like copyLibs
}
The project synchronizes without errors but when I run it, I get:
> Task :javacppBuildParser FAILED
Execution failed for task ':javacppBuildParser'.
> app/build/intermediates/javac/debug/classes/com/example/myjavacppapp/BuildConfig (wrong name: com/example/myjavacppapp/BuildConfig)
Is it beacause I didn't write anything inside javacppBuildCommand, javacppBuildParser and javacppBuildParser?
I know this is a basic question, but does anyone know what exactly I should write inside those blocks? I'm quite new to this and I don't know exactly where to look for this information.
After trying the solution presented in EDIT 1, above, I came across A guide on how to run Javacpp on Android studio together with gradle wiki page and as instructed there I have added this to my app's build.gradle file:
android {
applicationVariants.all { variant ->
variant.javaCompiler.doLast {
println 'javacpp ' + variant.name
javaexec {
main 'org.bytedeco.javacpp.tools.Builder'
classpath '/home/jacob/Work/other/sandbox/java/javacpp3/app/libs/javacpp.jar'
args '-cp', variant.javaCompiler.destinationDir,
'-properties', 'android-arm',
'-Dplatform.root=/home/jacob/.android/sdk/ndk/21.1.6352462',
'-Dplatform.compiler=/home/jacob/.android/sdk/ndk/21.1.6352462/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/bin/arm-linux-androideabi-g++',
'-Dplatform.includepath=/home/jacob/.android/sdk/ndk/21.1.6352462/sources/cxx-stl/gnu-libstdc++/include:src/main/cpp',
'-Dplatform.linkpath=/home/jacob/.android/sdk/ndk/21.1.6352462/sources/cxx-stl/llvm-libc++/libs/arm64-v8a',
'-d', 'libs/armeabi'
}
println 'javacpp done'
}
}
sourceSets.main {
jniLibs.srcDir 'libs'
jni.srcDirs = [] // disable automatic ndk-build call
}
}
The gradle sync runs ok but when I build the project I get:
> Task :app:compileDebugJavaWithJavac FAILED
javacpp debug
Exception in thread "main" java.lang.NoClassDefFoundError: androidx/appcompat/app/AppCompatActivity
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:467)
at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
at java.net.URLClassLoader$1.run(URLClassLoader.java:368)
at java.net.URLClassLoader$1.run(URLClassLoader.java:362)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:361)
at org.bytedeco.javacpp.tools.UserClassLoader.findClass(UserClassLoader.java:72)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:348)
at org.bytedeco.javacpp.tools.ClassScanner.addClass(ClassScanner.java:61)
at org.bytedeco.javacpp.tools.ClassScanner.addMatchingFile(ClassScanner.java:75)
at org.bytedeco.javacpp.tools.ClassScanner.addMatchingDir(ClassScanner.java:87)
at org.bytedeco.javacpp.tools.ClassScanner.addMatchingDir(ClassScanner.java:85)
at org.bytedeco.javacpp.tools.ClassScanner.addMatchingDir(ClassScanner.java:85)
at org.bytedeco.javacpp.tools.ClassScanner.addMatchingDir(ClassScanner.java:85)
at org.bytedeco.javacpp.tools.ClassScanner.addPackage(ClassScanner.java:99)
at org.bytedeco.javacpp.tools.Builder.classesOrPackages(Builder.java:672)
at org.bytedeco.javacpp.tools.Builder.main(Builder.java:962)
Caused by: java.lang.ClassNotFoundException: androidx.appcompat.app.AppCompatActivity
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at org.bytedeco.javacpp.tools.UserClassLoader.findClass(UserClassLoader.java:72)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 23 more
FAILURE: Build failed with an exception.
* Where:
Build file '/home/jacob/Work/other/sandbox/java/javacpp3/app/build.gradle' line: 48
* What went wrong:
Execution failed for task ':app:compileDebugJavaWithJavac'.
> Process 'command '/home/jacob/.android/studio/jre/bin/java'' finished with non-zero exit value 1
Any idea how I can solve this?
539
I've posted a complete working example here:
https://github.com/bytedeco/sample-projects/tree/master/gradle-javacpp-android
For reference, we can reproduce this project with these steps by:
app/build.gradle file (after applying in the usual manner the org.bytedeco.gradle-javacpp-build plugin), andandroid.applicationVariants.all { variant ->
def variantName = variant.name.capitalize() // either "Debug" or "Release"
def javaCompile = project.tasks.getByName("compile${variantName}JavaWithJavac")
def generateJson = project.tasks.getByName("generateJsonModel$variantName")
// Compiles NativeLibraryConfig.java
task "javacppCompileJava$variantName"(type: JavaCompile) {
include 'com/example/myapplication/NativeLibraryConfig.java'
source = javaCompile.source
classpath = javaCompile.classpath
destinationDir = javaCompile.destinationDir
}
// Parses NativeLibrary.h and outputs NativeLibrary.java
task "javacppBuildParser$variantName"(type: org.bytedeco.gradle.javacpp.BuildTask) {
dependsOn "javacppCompileJava$variantName"
classPath = [javaCompile.destinationDir]
includePath = ["$projectDir/src/main/cpp/"]
classOrPackageNames = ['com.example.myapplication.NativeLibraryConfig']
outputDirectory = file("$projectDir/src/main/java/")
}
// Compiles NativeLibrary.java and everything else
javaCompile.dependsOn "javacppBuildParser$variantName"
// Generates jnijavacpp.cpp and jniNativeLibrary.cpp
task "javacppBuildCompiler$variantName"(type: org.bytedeco.gradle.javacpp.BuildTask) {
dependsOn javaCompile
classPath = [javaCompile.destinationDir]
classOrPackageNames = ['com.example.myapplication.NativeLibrary']
compile = false
deleteJniFiles = false
outputDirectory = file("$projectDir/src/main/cpp/")
}
// Picks up the C++ files listed in CMakeLists.txt
generateJson.dependsOn "javacppBuildCompiler$variantName"
}
CMakeLists.txt file to include the generated .cpp files.
157
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