转：Android开发：使用JNI读取应用签名

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。