简单的Jni开发过程：
1、新建一个调用native的工具类，并且设置需要加载的动态so文件
public class JNIUtils {
static {
System.loadLibrary("JNIHello");
}
public static native String sayHelloFromJNI();
}
2、然后根据JNIUtils的包名以及类名生成对应的头文件（即.h文件），此处使用命令生成（快捷键alt + F12调出AS下的Terminal窗口）
cd app/src/main/java //进入项目的java文件夹
//新建与java同级的jni文件夹，并且在文件夹下生成.h文件
javah -d ../jni com.example.joy.jnidemo.JNIUtils
3、在.h文件同级文件夹下，新建c++文件JNIHello.cpp（根据需要新建C文件或者C++文件）
#include "com_example_joy_jnidemo_JNIUtils.h"
JNIEXPORT jstring JNICALL Java_com_example_joy_jnidemo_JNIUtils_sayHelloFromJNI
(JNIEnv *env, jclass jclass){
return env->NewStringUTF("Hello World From JNI!!!!!");
}
4、生成对应的so文件（两种生成方法）
方法一
：利用Android.mk、Application.mk生成so文件，步骤如下：
（1）新建Android.mk、Application.mk两个文件
Android.mk：
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := JNIHello #输出so文件的名称
LOCAL_SRC_FILES := JNIHello.cpp #需要读取的C++源文件地址
include $(BUILD_SHARED_LIBRARY)
Application.mk：
APP_STL := gnustl_static
APP_CPPFLAGS := -frtti -fexceptions
APP_ABI := all #生成所有版本的so文件
APP_PLATFORM := android-8
（2）在build.gradle文件中条件配置代码
apply plugin: 'com.android.application'
android {
compileSdkVersion 28
defaultConfig {
applicationId "com.example.joy.jnidemo"
minSdkVersion 24
targetSdkVersion 28
versionCode 1
versionName "1.0"
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
sourceSets {
main {
jni.srcDirs = []//禁止gradle 自动编译，使用已经编译好的So库
jniLibs.srcDirs = ['src/main/jniLibs']//指向要使用的库文件//的路径，前边的是自己项目的，后边的是第三方的so
}
}
}
task ndkBuild(type: Exec, description: 'Compile JNI source via NDK') {
//配置ndk的路径
commandLine "G:\\android-ndk-r20-windows-x86_64\\android-ndk-r20\\build\\ndk-build.cmd",
//ndk默认的生成so的文件
'NDK_PROJECT_PATH=build/intermediates/ndk',
//配置的我们想要生成的so文件所在的位置
'NDK_LIBS_OUT=src/main/jniLibs',
//指定项目以这个mk的方式
'APP_BUILD_SCRIPT=src/main/jni/Android.mk',
//指定项目以这个mk的方式
'NDK_APPLOCATION_MK=src/main/jni/Application.mk'
}
tasks.withType(JavaCompile) {
//使用ndkBuild
compileTask -> compileTask.dependsOn ndkBuild
}
dependencies {
implementation fileTree(include: ['*.jar'], dir: 'libs')
implementation 'com.android.support.constraint:constraint-layout:1.1.3'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:1.0.2'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
implementation 'com.android.support:appcompat-v7:28.0.0'
}
（3）点击rebulid project ，即可看见出现的jniLibs文件夹，以及文件夹下的so文件
方法二
：使用CMake工具生成so文件
（1）下载安装cmake相关工具：file-->setting...-->appearance&behavior--->system settings-->android sdk -->sdk tools-->选中CMake、LLDB下载安装
（2）新建CMakeLists.txt文件
# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html
# Sets the minimum version of CMake required to build the native library.
cmake_minimum_required(VERSION 3.4.1)
# 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.
add_library( # Sets the name of the library.
JNIHello #此处填入library名称
# Sets the library as a shared library.
SHARED
# Provides a relative path to your source file(s).
src/main/jni/JNIHello.cpp ) #此处填入c/C++文件路径
# 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.
JNIHello #此处填入library名称
# Links the target library to the log library
# included in the NDK.
${log-lib} )
（3）配置 build.gradle文件
apply plugin: 'com.android.application'
android {
compileSdkVersion 28
defaultConfig {
applicationId "com.example.joy.jnidemo2"
minSdkVersion 24
targetSdkVersion 28
versionCode 1
versionName "1.0"
testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
ndk{
moduleName "JNIHello"
}
externalNativeBuild {
cmake {
cppFlags ""
}
}
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
}
externalNativeBuild {
cmake {
path "CMakeLists.txt"
}
}
}
dependencies {
implementation fileTree(include: ['*.jar'], dir: 'libs')
implementation 'com.android.support.constraint:constraint-layout:1.1.3'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:1.0.2'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
implementation 'com.android.support:appcompat-v7:28.0.0'
}
（4）rebulid project
5、调用native方法
JNIUtils.sayHelloFromJNI();
注意：jni项目启动前，需要添加ndk，可以下载后在添加本地的ndk也可以直接在Android studio上直接下载
