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
");
    return 0;
}

jint ledCtrl(JNIEnv *env, jobject cls, jint which, jint status)
{
    printf("status of %d is %d 
", which, status);
    return 0;
}

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

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 -1;
     }
     jclass cls = (*env)->FindClass(env, "com/example/hardlibrary/HardControl"); //java里面类的路径
     if (cls == NULL) {
         return -1;
     }
     if((*env)->RegisterNatives(env,cls, gMethods, sizeof(gMethods)/sizeof(gMethods[0]))< 0) {
        return -1;
     }
    
     return JNI_VERSION_1_4;
}