博文转自http://www.tuicool.com/articles/UVjme2r,感谢博主的分享
为了防止被反编译，打算把关键代码写到so里(比如加解密)，在so里加上判断APk包签名是否一致的代码，避免so被二次打包。其实用JNI读签名就是用了Java的反射机制。
先看Java读取签名的方法:
try {
PackageInfo info = context.getPackageManager().getPackageInfo(context.getPackageName(), 64);
Signature sign = info.signatures[0];
Log.i("test", "hashCode : " + sign.hashCode());
} catch (NameNotFoundException e) {
e.printStackTrace();
}
然后我们用JNI c语言实现,同样需要传递Context：
int getSignHashCode(JNIEnv *env, jobject context) {
//Context的类
jclass context_clazz = (*env)->GetObjectClass(env, context);
// 得到 getPackageManager 方法的 ID
jmethodID methodID_getPackageManager = (*env)->GetMethodID(env, context_clazz,
"getPackageManager", "()Landroid/content/pm/PackageManager;");
// 获得PackageManager对象
jobject packageManager = (*env)->CallObjectMethod(env, context,
methodID_getPackageManager);
// // 获得 PackageManager 类
jclass pm_clazz = (*env)->GetObjectClass(env, packageManager);
// 得到 getPackageInfo 方法的 ID
jmethodID methodID_pm = (*env)->GetMethodID(env, pm_clazz, "getPackageInfo",
"(Ljava/lang/String;I)Landroid/content/pm/PackageInfo;");
//
// // 得到 getPackageName 方法的 ID
jmethodID methodID_pack = (*env)->GetMethodID(env, context_clazz,
"getPackageName", "()Ljava/lang/String;");
// 获得当前应用的包名
jstring application_package = (*env)->CallObjectMethod(env, context,
methodID_pack);
const char *str = (*env)->GetStringUTFChars(env, application_package, 0);
__android_log_print(ANDROID_LOG_DEBUG, "JNI", "packageName: %s\n", str);
// 获得PackageInfo
jobject packageInfo = (*env)->CallObjectMethod(env, packageManager,
methodID_pm, application_package, 64);
jclass packageinfo_clazz = (*env)->GetObjectClass(env, packageInfo);
jfieldID fieldID_signatures = (*env)->GetFieldID(env, packageinfo_clazz,
"signatures", "[Landroid/content/pm/Signature;");
jobjectArray signature_arr = (jobjectArray)(*env)->GetObjectField(env,
packageInfo, fieldID_signatures);
//Signature数组中取出第一个元素
jobject signature = (*env)->GetObjectArrayElement(env, signature_arr, 0);
//读signature的hashcode
jclass signature_clazz = (*env)->GetObjectClass(env, signature);
jmethodID methodID_hashcode = (*env)->GetMethodID(env, signature_clazz,
"hashCode", "()I");
jint hashCode = (*env)->CallIntMethod(env, signature, methodID_hashcode);
__android_log_print(ANDROID_LOG_DEBUG, "JNI", "hashcode: %d\n", hashCode);
return hashCode;
}
第二个参数jobject不是JNI函数的默认参数，而是传入的Context实例。