Android(安卓)APK JNI sample (JAVA JNI)
16lz
2021-01-25
一个小实例介绍 Android JNI 如何实现步骤,其中有个遇到的加载库失败的教训:
1. 编写JAVA代码,写明要调用的本地动态链接库的本地方法:
wnplib.javapublic class wnplib{ public native void SayHello(String name); static { System.loadLibrary("wnp"); } public static void main(String [] argv) { wnplib wp = new wnplib(); wp.SayHello("myName"); }}
2. 编译javac 成.class文件
javac wnplib.java
3. 使用javah 生成该类对应的C语言.h文件
javah -classpath . wnplib
4. 使用C/C++实现C的各函数
5. 在Android Source code 中编译代码生成.so库文件
注意:此处需要注意,目前Android 有两种支持ARM 和 X86 两种,在不同的代码里编译的库有限制,是不是能弄个不依赖的? NDK编译我还没有实验。
当编译ARM 和 X86 不一致的.so会出现如下的错误:
08-14 16:24:58.572 I/ActivityManager( 240): Start proc jni.wnptest.wnpjnitest for activity jni.wnptest.wnpjnitest/.WnptestActivity: pid=22268 uid=10000 gids={}08-14 16:24:58.592 E/jdwp (22268): Failed sending reply to debugger: Broken pipe08-14 16:24:58.592 D/dalvikvm(22268): Debugger has detached; object registry had 1 entries08-14 16:24:58.602 D/WNP-TEST(22268): /vendor/lib:/system/lib:/system/lib/arm08-14 16:24:58.612 D/houdini (22268): [22268] Loading library(version: 2.0.7.42789 RELEASE)... successfully.08-14 16:24:58.612 D/houdini (22268): [22268] Open Native Library /system/lib/libwnp.so failed.08-14 16:24:58.612 W/dalvikvm(22268): Exception Ljava/lang/UnsatisfiedLinkError; thrown while initializing Ljni/wnptest/wnpjnitest/WnptestActivity;08-14 16:24:58.612 W/dalvikvm(22268): Class init failed in newInstance call (Ljni/wnptest/wnpjnitest/WnptestActivity;)08-14 16:24:58.612 D/AndroidRuntime(22268): Shutting down VM08-14 16:24:58.612 W/dalvikvm(22268): threadid=1: thread exiting with uncaught exception (group=0x4194e6f0)08-14 16:24:58.612 I/Process (22268): Sending signal. PID: 22268 SIG: 908-14 16:24:58.612 E/AndroidRuntime(22268): FATAL EXCEPTION: main08-14 16:24:58.612 E/AndroidRuntime(22268): java.lang.ExceptionInInitializerError08-14 16:24:58.612 E/AndroidRuntime(22268): at java.lang.Class.newInstanceImpl(Native Method)08-14 16:24:58.612 E/AndroidRuntime(22268): at java.lang.Class.newInstance(Class.java:1319)08-14 16:24:58.612 E/AndroidRuntime(22268): at android.app.Instrumentation.newActivity(Instrumentation.java:1023)08-14 16:24:58.612 E/AndroidRuntime(22268): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1872)08-14 16:24:58.612 E/AndroidRuntime(22268): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1984)08-14 16:24:58.612 E/AndroidRuntime(22268): at android.app.ActivityThread.access$600(ActivityThread.java:124)08-14 16:24:58.612 E/AndroidRuntime(22268): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1148)08-14 16:24:58.612 E/AndroidRuntime(22268): at android.os.Handler.dispatchMessage(Handler.java:99)08-14 16:24:58.612 E/AndroidRuntime(22268): at android.os.Looper.loop(Looper.java:137)08-14 16:24:58.612 E/AndroidRuntime(22268): at android.app.ActivityThread.main(ActivityThread.java:4436)08-14 16:24:58.612 E/AndroidRuntime(22268): at java.lang.reflect.Method.invokeNative(Native Method)08-14 16:24:58.612 E/AndroidRuntime(22268): at java.lang.reflect.Method.invoke(Method.java:511)08-14 16:24:58.612 E/AndroidRuntime(22268): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)08-14 16:24:58.612 E/AndroidRuntime(22268): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)08-14 16:24:58.612 E/AndroidRuntime(22268): at dalvik.system.NativeStart.main(Native Method)08-14 16:24:58.612 E/AndroidRuntime(22268): Caused by: java.lang.UnsatisfiedLinkError: Cannot load library: get_lib_extents[753]: 121 - /system/lib/libwnp.so is not a valid ELF object08-14 16:24:58.612 E/AndroidRuntime(22268): at java.lang.Runtime.loadLibrary(Runtime.java:370)08-14 16:24:58.612 E/AndroidRuntime(22268): at java.lang.System.loadLibrary(System.java:535)08-14 16:24:58.612 E/AndroidRuntime(22268): at jni.wnptest.wnpjnitest.WnptestActivity.(WnptestActivity.java:39)08-14 16:24:58.612 E/AndroidRuntime(22268): ... 15 more08-14 16:24:58.612 W/ActivityManager( 240): Force finishing activity jni.wnptest.wnpjnitest/.WnptestActivity
6. Android APK 测试代码:
注意:在加载库的时候需要 去掉库前缀字符串"lib", libwnp.so 加载的时候只需写wnp即可。
package jni.wnptest.wnpjnitest;import android.app.Activity;import android.os.Bundle;import android.util.Log;public class WnptestActivity extends Activity { /* * Create a game room. */ public native int wnpCreateRoom(int port); static { Log.d("WNP-TEST", System.getProperty("java.library.path")); //System.out.println(System.getProperty("java.library.path")); try { System.loadLibrary("wnp"); } catch (UnsatisfiedLinkError ule) { System.err.println("WARNING: Could not load library!"); } } /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); }}
7. 注意Android APK 加载库需要在JNI中指定JAVA测试的类名及路径
*Java Application class path */static const char *classPathName = "jni/wnptest/wnpjnitest/WnptestActivity";static JNINativeMethod methods[] = { {"wnpSendDdata", "([BI)I", (void*)JNICALL Java_WNP_wnpSendDdata }, {"wnpGetData", "()[B", (void*)JNICALL Java_WNP_wnpGetData }, {"wnpCreateRoom", "(I)I", (void*)JNICALL Java_WNP_wnpCreateRoom }, {"wnpJoinRoom", "(Ljava/lang/String;I)I", (void*)JNICALL Java_WNP_wnpJoinRoom }, {"wnpQuitRoom", "()I", (void*)JNICALL Java_WNP_wnpQuitRoom },};/* * Register methods for one class. */static int registerNativeMethods(JNIEnv* env, const char* className, JNINativeMethod* gMethods, int numMethods){ jclass clazz; clazz = (*env)->FindClass(env, className); if (clazz == NULL) return JNI_FALSE; if ((*env)->RegisterNatives(env, clazz, gMethods, numMethods) < 0) { printf("register nativers error"); return JNI_FALSE; } return JNI_TRUE;}/* * Register methods for all classes. * * returns JNI_TRUE on success. */static int registerNatives(JNIEnv* env){ if (!registerNativeMethods(env, classPathName, methods, sizeof(methods) / sizeof(methods[0]))) { return JNI_FALSE; } return JNI_TRUE;}/* * Called by the VM when the shared library is loaded. */jint JNI_OnLoad(JavaVM* vm, void* reserved){ JNIEnv* env = NULL; jint result = -1; WNP_LOGD("Entering JNI_OnLoad\n"); if ((*vm)->GetEnv(vm, (void**) &env, JNI_VERSION_1_6) != JNI_OK) goto bail; assert(env != NULL); if (!registerNatives(env)) goto bail; /* success -- return valid version number */ result = JNI_VERSION_1_6;bail: printf("Leaving JNI_OnLoad (result=0x%x)\n", result); return result;}
8. 好的现在你可以测试实现的JNI了。
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