android ndk-build 编译静态库libxx.a
需求场景：
目前有安卓编码好的现在的openssl的两个.a,我们需要调用openssl的函数，并把功能再封装成.a;
这样使用时，在android studio jni项目 cmake 里面，需要先引用openssl的.a再引用 上面封装的.a;
如果使用so，那么，直接在android studio jni项目的 cpp里面直接调用openssl的方法，对外提供jni java接口，打包成so即可；
先来说用ndk-build 打包 libxx.a吧，并在打包的时候引用openssl的静态库.a
1. 首先当前目录下准备好 编码好的openssl静态库，如下图示，安卓平台的
2. 测试使用的源文件，我这里在.h声明一个封装的方法 ssl_sha,并且在.c 实现里面，调用 openssl 的SHA256接口；如下
加 #ifdef __cplusplus 是为了在jni调用时，cpp里面出现未定义的错误，如下 ssl_hash.h
#ifndef ssl_hash_h#define ssl_hash_h# ifdef __cplusplusextern "C" {#endif#include /* * openssl sha256 * */int ssl_sha256(const char *in_data,int in_len,char *out_hash);# ifdef __cplusplus}# endif#endif /* ssl_hash_h */
如下 ssl_hash.c 实现文件
#include "ssl_hash.h"#include "openssl/sha.h"int ssl_sha256(const char *in_data,int in_len,char *out_hash){ if (!in_data) { return -100; } if (!SHA256((const unsigned char *)in_data, in_len, (unsigned char *)out_hash)) { return -1001; } return 1;} 同样这两文件也要放在 .mk的同一目录；
3. 开始编写 Android.mk,Application.mk, 如下示例
#Android.mk文件LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS)#编码后生成的.a的名称LOCAL_MODULE := sslhash #要编码的源文件c或cppLOCAL_SRC_FILES := ssl_hash.c#依赖的静态库.a，若要使用动态库使用LOCAL_SHARED_LIBRARIES .soLOCAL_STATIC_LIBRARIES := libs/${TARGET_ARCH_ABI}/lib/libssl.a libs/${TARGET_ARCH_ABI}/lib/libcrypto.a#依赖的静态库的头文件LOCAL_C_INCLUDES := libs/${TARGET_ARCH_ABI}/include#最后生成静态库include $(BUILD_STATIC_LIBRARY) #Application.mk 这里测试，只编译出x86的APP_ABI := x86
4. 所有文件都准备好之后如下图示：
5. 调用ndk-build 开始编译
~/Library/Android/sdk/ndk-bundle/ndk-build NDK_PROJECT_PATH=./ NDK_LIBS_OUT=./ APP_BUILD_SCRIPT=./Android.mk NDK_APPLICATION_MK=./Application.mk
6. 成功之后会在当前目录下生成 obj目录，里面包含生成的 静态库libxx.a
7. 编译好之后，下面需要在Android studio 中测试；用as 创建一个jni项目；
8.在工程build.gradle(Module:app) 里面添加 libs目录 （Android 视图）
externalNativeBuild { cmake { path "CMakeLists.txt" } } sourceSets { main { jniLibs.srcDirs = ['libs'] } } 并且在指定测试只编译 x86
externalNativeBuild { cmake { cppFlags "" abiFilters "x86" } } ndk{ abiFilters "x86" } 9. 将之前libs目录的openssl库全部copy到 工程 jnilibs目录 (Android 视图）
并把生成的libsslhash.a放到 x86/lib下
并把ssl_hash.h头文件放到x86/include下
放到哪都行，需要在cmake里面指定引用好
10. 打开CmakeList.txt 配置openssl静态库的引用，以及配置引用生成的libsslhash.a
如下完善的cmakelist
cmake_minimum_required(VERSION 3.4.1)set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++11")#这里配置指定目录libsset(OpenSSL_DIR ${CMAKE_SOURCE_DIR}/libs)# 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.#这里引用三个静态.a, ssl,sslhash,cryptoadd_library(crypto STATIC IMPORTED)add_library(ssl STATIC IMPORTED)add_library(sslhash STATIC IMPORTED)# 这里加载，并且找到相应的 libxxx.aset_target_properties( # Specifies the target library. crypto # Specifies the parameter you want to define. PROPERTIES IMPORTED_LOCATION # Provides the path to the library you want to import. ${OpenSSL_DIR}/${ANDROID_ABI}/lib/libcrypto.a )set_target_properties( # Specifies the target library. ssl # Specifies the parameter you want to define. PROPERTIES IMPORTED_LOCATION # Provides the path to the library you want to import. ${OpenSSL_DIR}/${ANDROID_ABI}/lib/libssl.a ) set_target_properties( # Specifies the target library. sslhash # Specifies the parameter you want to define. PROPERTIES IMPORTED_LOCATION # Provides the path to the library you want to import. ${OpenSSL_DIR}/${ANDROID_ABI}/lib/libsslhash.a)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). src/main/cpp/native-lib.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.#这里openssl需要 zlib库，加载系统的find_library( z-lib z )#这里指定一下咱的头文件目录，openssl头文件，以及咱封装的ssl_hash.h头文件include_directories( ${OpenSSL_DIR}/${ANDROID_ABI}/include ${OpenSSL_DIR}/${ANDROID_ABI}/)#最后一步连接，这里注意，一定要把sslhash,咱封装的这个.a放到ssl,crypto的前面，不然报错说方法未定义，可能因为sslhash引用了openssl的东西，target_link_libraries( # Specifies the target library. native-lib # Links the target library to the log library # included in the NDK. sslhash ssl crypto ${log-lib} ${z-lib})
11. 配置完成，如果编译不出问题就可以写jni调用测试了；
在 MainActitity.java里面，添加一下jni方法
public native String stringFromJNI(); //添加的测试方法 public native int sslsha(byte[] indata,int inlen,byte[] outhash);
12. 在native-lib.cpp 里面实现jni方法
#include "ssl_hash.h"extern "C"JNIEXPORT jint JNICALLJava_androidapp_cocoajin_com_tjni_MainActivity_sslsha(JNIEnv *env, jobject instance, jbyteArray indata_, jint inlen, jbyteArray outhash_) { jbyte *indata = env->GetByteArrayElements(indata_, NULL); jbyte *outhash = env->GetByteArrayElements(outhash_, NULL); int ret = ssl_sha256((const char *)indata,inlen,(char *)outhash); env->ReleaseByteArrayElements(indata_, indata, 0); env->ReleaseByteArrayElements(outhash_, outhash, 0); return ret;}//默认系统的extern "C"JNIEXPORT jstring JNICALLJava_androidapp_cocoajin_com_tjni_MainActivity_stringFromJNI( JNIEnv *env, jobject /* this */) { std::string hello = "Hello from C++"; return env->NewStringUTF(hello.c_str());}
13. 最后调用 ，这里把byte[] 转成了hexString显示在了app上
// Example of a call to a native method TextView tv = (TextView) findViewById(R.id.sample_text); String he = "hello"; byte[] habb = new byte[32]; sslsha(he.getBytes(),he.length(),habb); tv.setText(ByteHexUtil.bytesToHexString(habb));
14. 执行结果，以及验证结果
15: 参考资料与 工程下载