JNI模板

java爲了調用底層驅動函數，須要調用外部的C/C++代碼，java提供了JNI接口：

而後將C代碼編譯成庫（windows下 .dll / android環境下 .so）

arm-linux-gcc -fPIC -shared hardcontrol.c -o libhardcontrol.so -I /usr/lib/jvm/java-1.7.0-openjdk-amd64/include -nostdlib /work/android-5.0.2/prebuilts/ndk/9/platforms/android-19/arch-arm/usr/lib/libc.so -I /work/android-5.0.2/prebuilts/ndk/9/platforms/android-19/arch-arm/usr/include /work/android-5.0.2/prebuilts/ndk/9/platforms/android-19/arch-arm/usr/lib/liblog.so

arm-linux-gcc -fPIC -shared jni_test.c -o libtesthw.so  -I /usr/lib/jvm/java-1.7.0-openjdk-amd64/include -nostdlib /work/android-5.0.2/prebuiltoid-19/arch-arm/usr/lib/libc.ss/ndk/9/platforms/android-19/arch-arm/usr/lib/libc.so -I /work/android-5.0.2/prebuilts/ndk/9/pla-5.0.2/prebuilts/ndk/9/platfortforms/android-19/arch-arm/usr/include /work/android-5.0.2/prebuilts/ndk/9/platforms/android-19/arch-arm/usr/lib/liblog.so -nostdlib /work/android-5.0.2/prebuilts/ndk/9/platforms/android-19/arch-arm/usr/lib/libm.so

而後將生成的動態連接庫放到android studio工程的app/lib目錄下：

新建armeabi子目錄，放入.so文件

static{
       System.loadLibrary("hardcontrol");               //指定動態庫
};

修改app路徑下的build.gradle：

加上

sourceSets {
    main {
        jniLibs.srcDirs = ["libs"]
    }
}

 1 #include <stdio.h>
 2 #include <jni.h>
 3 
 4 jint ledOpen(JNIEnv *env, jobject cls)  5 {  6     printf("all led opened\n");  7     return 0;  8 }  9 
10 jint ledCtrl(JNIEnv *env, jobject cls, jint which, jint status) 11 { 12     printf("status of %d is %d \n", which, status); 13     return 0; 14 } 15 
16 void ledClose(JNIEnv *env, jobject cls) 17 { 18     printf("all led closed\n"); 19 } 20 
21 static JNINativeMethod gMethods[] ={ 22     {"ledCtrl", "(II)I", (void *)ledCtrl}, 23     {"ledOpen", "()I", (void *)ledOpen}, 24     {"ledClose", "()V", (void *)ledClose}, 25 }; 26 
27 
28 JNIEXPORT jint JNICALL 29 JNI_OnLoad(JavaVM *jvm, void *reserved) 30 { 31      JNIEnv *env;  //struct JNINativeInterface_ *
32      
33      if ((*jvm)->GetEnv(jvm, (void**) &env, JNI_VERSION_1_4)) { 34         return -1; 35  } 36      jclass cls = (*env)->FindClass(env, "com/example/hardlibrary/HardControl"); //java裏面類的路徑
37      if (cls == NULL) { 38          return -1; 39  } 40      if((*env)->RegisterNatives(env,cls, gMethods, sizeof(gMethods)/sizeof(gMethods[0]))< 0) { 41         return -1; 42  } 43     
44      return JNI_VERSION_1_4; 45 }