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"]
    }
}

 1 #include <stdio.h>
 2 #include <jni.h>
 3 
 4 jint ledOpen(JNIEnv *env, jobject cls)
 5 {
 6     printf("all led opened
");
 7     return 0;
 8 }
 9 
10 jint ledCtrl(JNIEnv *env, jobject cls, jint which, jint status)
11 {
12     printf("status of %d is %d 
", which, status);
13     return 0;
14 }
15 
16 void ledClose(JNIEnv *env, jobject cls)
17 {
18     printf("all led closed
");
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里面类的路径
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 }