1.首先认识一下NDK。
（1）什么是NDK？
NDK全称是Native Development Kit，NDK提供了一系列的工具，帮助开发者快速开发C/C++的动态库，并能自动将so和java应用一起打包成apk。NDK集成了交叉编译器（交叉编译器需要UNIX或LINUX系统环境），并提供了相应的mk文件隔离CPU、平台、ABI等差异，开发人员只需要简单修改mk文件（指出“哪些文件需要编译”、“编译特性要求”等），就可以创建出so。
（2）为什么使用NDK？
1）代码的保护：由于apk的java层代码很容易被反编译，而C/C++库反汇难度较大。
2）可以方便地使用现存的开源库：大部分现存的开源库都是用C/C++代码编写的。
3）提高程序的执行效率：将要求高性能的应用逻辑使用C开发，从而提高应用程序的执行效率。
4）便于移植：用C/C++写得库可以方便在其他的嵌入式平台上再次使用。
（3）什么是JNI？
JNI全称为：Java Native Interface。JNI是本地编程接口，它使得在 Java 虚拟机内部运行的 Java代码能够与用其它语言(如 C、C++)编写的代码进行交互。
（4）为什么使用JNI？
JNI的目的是使java方法能够调用C/C++实现的一些函数。
（5）安卓中的so文件是什么？
Android中用到的so文件是一个C/C++的函数库。在android的JNI中，要先将相应的C/C++打包成so库，然后导入到lib文件夹中供java调用。
2.Android Studio 配置NDK（使用Android Studio 4.2.2之后的稳定版本）
（1） 步骤一：点击红圈处（这是Mac配置流程，Windows对应的按钮是Settings），如下图一
（2）步骤二：下载下图一中第3步红圈中的一个NDK和一个CMake，下载成功后如下图一所示（建议下载前先配置Android Studio 国内镜像代理，详见：Android Studio 国内镜像代理设置（如果设置之后还是远程仓库下载失败，请仔细阅读其内容就可以解决了）_android studio 镜像_ErwinNakajima的博客-CSDN博客）。
3.开始开发，在main文件夹下面创建一个cpp文件夹，如下图一和下圖二，然后在cpp文件夹下创建native-lib.cpp、return-data.cpp和CMakeLists.txt，然后添加具体内容；
native-lib.cpp文件的内容；
//// Created by ErwinNakashima on /12/24.//#include <jni.h>#include <stdio.h>#include <string.h>#include <string>static jclass contextClass;static jclass signatureClass;static jclass packageNameClass;static jclass packageInfoClass;/**之前生成好的签名字符串*/const char *SIGN_RELEASE = "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";const char *SIGN_DEBUG = "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";std::string hello = "(*^__^*) 嘻嘻……~Hello from C++ 特朗普的头发是黄色的";/*根据context对象,获取签名字符串*/const char *getSignString(JNIEnv *env, jobject contextObject) {jmethodID getPackageManagerId = (env)->GetMethodID(contextClass, "getPackageManager","()Landroid/content/pm/PackageManager;");jmethodID getPackageNameId = (env)->GetMethodID(contextClass, "getPackageName","()Ljava/lang/String;");jmethodID signToStringId = (env)->GetMethodID(signatureClass, "toCharsString","()Ljava/lang/String;");jmethodID getPackageInfoId = (env)->GetMethodID(packageNameClass, "getPackageInfo","(Ljava/lang/String;I)Landroid/content/pm/PackageInfo;");jobject packageManagerObject = (env)->CallObjectMethod(contextObject, getPackageManagerId);jstring packNameString = (jstring) (env)->CallObjectMethod(contextObject, getPackageNameId);jobject packageInfoObject = (env)->CallObjectMethod(packageManagerObject, getPackageInfoId,packNameString, 64);jfieldID signaturefieldID = (env)->GetFieldID(packageInfoClass, "signatures","[Landroid/content/pm/Signature;");jobjectArray signatureArray = (jobjectArray) (env)->GetObjectField(packageInfoObject,signaturefieldID);jobject signatureObject = (env)->GetObjectArrayElement(signatureArray, 0);return (env)->GetStringUTFChars((jstring) (env)->CallObjectMethod(signatureObject, signToStringId), 0);}extern "C"JNIEXPORT jstring JNICALLJava_com_phone_library_1common_JavaGetData_nativeGetString(JNIEnv *env, jclass clazz,jobject context, jboolean is_release) {const char *signStrng = getSignString(env, context);bool isRelease = is_release;const char *SIGN;if (isRelease) {SIGN = SIGN_RELEASE;} else {SIGN = SIGN_DEBUG;}if (strcmp(signStrng, SIGN) == 0)//签名一致 返回合法的 api key，否则返回错误{return (env)->NewStringUTF(hello.c_str());} else {return (env)->NewStringUTF("error");}}//bool toCppBool(jboolean value) {// return value == JNI_TRUE;//}/**利用OnLoad钩子,初始化需要用到的Class类.*/JNIEXPORT jintJNICALL JNI_OnLoad(JavaVM *vm, void *reserved) {JNIEnv *env = NULL;jint result = -1;if (vm->GetEnv((void **) &env, JNI_VERSION_1_4) != JNI_OK)return result;contextClass = (jclass) env->NewGlobalRef((env)->FindClass("android/content/Context"));signatureClass = (jclass) env->NewGlobalRef((env)->FindClass("android/content/pm/Signature"));packageNameClass = (jclass) env->NewGlobalRef((env)->FindClass("android/content/pm/PackageManager"));packageInfoClass = (jclass) env->NewGlobalRef((env)->FindClass("android/content/pm/PackageInfo"));return JNI_VERSION_1_4;}
return-data.cpp文件的内容；
#include <jni.h>#include <stdio.h>#include <string.h>#ifdef __cplusplusextern "C" {#endifstatic jclass contextClass;static jclass signatureClass;static jclass packageNameClass;static jclass packageInfoClass;/**之前生成好的签名字符串*/const char *SIGN_RELEASE = "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";const char *SIGN_DEBUG = "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";const char *aesKey = "rxjava_and_re_ro";const char *databaseEncryptKey = "Aa123456";/*根据context对象,获取签名字符串*/const char *getSignString(JNIEnv *env, jobject contextObject) {jmethodID getPackageManagerId = (env)->GetMethodID(contextClass, "getPackageManager","()Landroid/content/pm/PackageManager;");jmethodID getPackageNameId = (env)->GetMethodID(contextClass, "getPackageName","()Ljava/lang/String;");jmethodID signToStringId = (env)->GetMethodID(signatureClass, "toCharsString","()Ljava/lang/String;");jmethodID getPackageInfoId = (env)->GetMethodID(packageNameClass, "getPackageInfo","(Ljava/lang/String;I)Landroid/content/pm/PackageInfo;");jobject packageManagerObject = (env)->CallObjectMethod(contextObject, getPackageManagerId);jstring packNameString = (jstring) (env)->CallObjectMethod(contextObject, getPackageNameId);jobject packageInfoObject = (env)->CallObjectMethod(packageManagerObject, getPackageInfoId,packNameString, 64);jfieldID signaturefieldID = (env)->GetFieldID(packageInfoClass, "signatures","[Landroid/content/pm/Signature;");jobjectArray signatureArray = (jobjectArray) (env)->GetObjectField(packageInfoObject,signaturefieldID);jobject signatureObject = (env)->GetObjectArrayElement(signatureArray, 0);return (env)->GetStringUTFChars((jstring) (env)->CallObjectMethod(signatureObject, signToStringId), 0);}extern "C"JNIEXPORT jstring JNICALLJava_com_phone_library_1common_JavaGetData_nativeAesKey(JNIEnv *env, jclass clazz, jobject context,jboolean is_release) {const char *signStrng = getSignString(env, context);bool isRelease = is_release;const char *SIGN;if (isRelease) {SIGN = SIGN_RELEASE;} else {SIGN = SIGN_DEBUG;}if (strcmp(signStrng, SIGN) == 0)//签名一致 返回合法的 api key，否则返回错误{return (env)->NewStringUTF(aesKey);} else {return (env)->NewStringUTF("error");}}extern "C"JNIEXPORT jstring JNICALLJava_com_phone_library_1common_JavaGetData_nativeDatabaseEncryptKey(JNIEnv *env, jclass clazz,jobject context,jboolean is_release) {const char *signStrng = getSignString(env, context);bool isRelease = is_release;const char *SIGN;if (isRelease) {SIGN = SIGN_RELEASE;} else {SIGN = SIGN_DEBUG;}if (strcmp(signStrng, SIGN) == 0)//签名一致 返回合法的 api key，否则返回错误{return (env)->NewStringUTF(databaseEncryptKey);} else {return (env)->NewStringUTF("error");}}/**利用OnLoad钩子,初始化需要用到的Class类.*/JNIEXPORT jintJNICALL JNI_OnLoad(JavaVM *vm, void *reserved) {JNIEnv *env = NULL;jint result = -1;if (vm->GetEnv((void **) &env, JNI_VERSION_1_4) != JNI_OK)return result;contextClass = (jclass) env->NewGlobalRef((env)->FindClass("android/content/Context"));signatureClass = (jclass) env->NewGlobalRef((env)->FindClass("android/content/pm/Signature"));packageNameClass = (jclass) env->NewGlobalRef((env)->FindClass("android/content/pm/PackageManager"));packageInfoClass = (jclass) env->NewGlobalRef((env)->FindClass("android/content/pm/PackageInfo"));return JNI_VERSION_1_4;}#ifdef __cplusplus}#endif
CMakeLists.txt的內容。
# For more information about using CMake with Android Studio, read the# documentation: /studio/projects/add-native-code.html# Sets the minimum version of CMake required to build the native library.cmake_minimum_required(VERSION 3.10.2)# Creates and names a library, sets it as either STATIC# or SHARED, and provides the relative paths to its source code.# You can define multiple libraries, and CMake builds them for you.# Gradle automatically packages shared libraries with your APK.#设置so库的输出路径set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${PROJECT_SOURCE_DIR}/libs/${ANDROID_ABI})add_library( # Sets the name of the library.native-lib# Sets the library as a shared library.SHARED# Provides a relative path to your source file(s).native-lib.cpp)add_library( # Sets the name of the library.return-data# Sets the library as a shared library.SHARED# Provides a relative path to your source file(s).return-data.cpp)# Searches for a specified prebuilt library and stores the path as a# variable. Because CMake includes system libraries in the search path by# default, you only need to specify the name of the public NDK library# you want to add. CMake verifies that the library exists before# completing its build.find_library( # Sets the name of the path variable.log-lib# Specifies the name of the NDK library that# you want CMake to locate.log)# Specifies libraries CMake should link to your target library. You# can link multiple libraries, such as libraries you define in this# build script, prebuilt third-party libraries, or system libraries.target_link_libraries( # Specifies the target library.native-libreturn-data# Links the target library to the log library# included in the NDK.${log-lib})
4.配置ndk，在module的build.gradle文件下的android下配置；
sourceSets {main {jniLibs.srcDirs = ['libs']}}ndkVersion '16.1.4479499'externalNativeBuild {cmake {path file('src/main/cpp/CMakeLists.txt')version '3.10.2'}}
module的build.gradle文件下的defaultConfig下配置；
ndk {//选择要添加的对应 cpu 类型的 .so 库。abiFilters 'armeabi-v7a', 'arm64-v8a'// abiFilters 'armeabi-v7a', 'arm64-v8a'// 还可以添加 'x86', 'x86_64', 'mips', 'mips64'}
項目的gradle.properties文件下配置，如下图一；
android.useDeprecatedNdk=true
項目的local.properties文件下配置，如下图一。
ndk.dir=/Users/erwinnakashima/Library/Android/sdk/ndk/16.1.4479499
5.添加JavaGetData文件，JavaGetData文件内容；
package com.phone.library_common;import android.content.Context;public class JavaGetData {static {System.loadLibrary("return-data");System.loadLibrary("native-lib");}public static native String nativeAesKey(Context context, boolean isRelease);public static native String nativeDatabaseEncryptKey(Context context, boolean isRelease);public static native String nativeGetString(Context context, boolean isRelease);}
在Application的onCreate方法中调用JavaGetData.nativeAesKey()，然后ReBuild Project。就会生成两个文件这几个so文件，如下图一，然后就能正常获取到C++文件（也就是cpp文件）中的数据了，还可以把so动态库提供给第三方使用，具体方式详见Android 项目调用第三方库so动态库_ErwinNakajima的博客-CSDN博客
如对此有疑问，请联系qq1164688204。
推荐Android开源项目
项目功能介绍：原本是RxJava2 和Retrofit2 项目，现已更新使用Kotlin+RxJava2+Retrofit2+MVP架构+组件化和
Kotlin+Retrofit2+协程+MVVM架构+组件化， 添加自动管理token 功能，添加RxJava2 生命周期管理，集成极光推送、阿里云Oss对象存储和高德地图定位功能。
项目地址：/urasaki/RxJava2AndRetrofit2
Android Studio 进行NDK开发 实现JNI 以及编写C++与Java交互（Java调用本地函数）并编译出本地so动态库
