JNI模板

java为了调用底层驱动函数，需要调用外部的C/C++代码，java提供了JNI接口：

然后将C代码编译成库（windows下 .dll / android环境下 .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

然后将生成的动态链接库放到android studio工程的app/lib目录下：

新建armeabi子目录，放入.so文件

static{
       System.loadLibrary("hardcontrol");               //指定动态库
};

修改app路径下的build.gradle：

加上

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

 #include <stdio.h>
 #include <jni.h>

 jint ledOpen(JNIEnv *env, jobject cls)
 {
     printf("all led opened\n");
     return ;
 }

 jint ledCtrl(JNIEnv *env, jobject cls, jint which, jint status)
 {
     printf("status of %d is %d \n", which, status);
     return ;
 }

 void ledClose(JNIEnv *env, jobject cls)
 {
     printf("all led closed\n");
 }

 static JNINativeMethod gMethods[] ={
     {"ledCtrl", "(II)I", (void *)ledCtrl},
     {"ledOpen", "()I", (void *)ledOpen},
     {"ledClose", "()V", (void *)ledClose},
 };

 JNIEXPORT jint JNICALL
 JNI_OnLoad(JavaVM *jvm, void *reserved)
 {
      JNIEnv *env;  //struct JNINativeInterface_ *

      if ((*jvm)->GetEnv(jvm, (void**) &env, JNI_VERSION_1_4)) {
         return -;
      }
      jclass cls = (*env)->FindClass(env, "com/example/hardlibrary/HardControl"); //java里面类的路径
      if (cls == NULL) {
          return -;
      }
      if((*env)->RegisterNatives(env,cls, gMethods, sizeof(gMethods)/sizeof(gMethods[]))< ) {
         return -;
      }

      return JNI_VERSION_1_4;
 }