Android JNI开发从0到1，java调C，C调Java，保姆级教程详解

前些天发现了一个蛮有意思的人工智能学习网站,8个字形容一下"通俗易懂，风趣幽默"，感觉非常有意思,忍不住分享一下给大家。
👉点击跳转到教程

第一步首先配置Android studio的NDK开发环境，首先在Android studio中下载NDK包

第二步在local.properties文件中，配置对应的NDK路径

第三歩，在app目录下的build.gradle文件中的，android{}闭包中，指定CMakeLists.txt路径

// 在android节点下// 指定CMakeLists.txt路径externalNativeBuild {cmake {// 在该文件种设置所要编写的c源码位置，以及编译后so文件的名字path 'CMakeLists.txt'}}

在defaultConfig闭包下配置

// 增加cmake控制属性externalNativeBuild {cmake {// 指定编译架构abiFilters 'arm64-v8a', 'armeabi-v7a', 'x86', 'x86_64'}}

在app目录下，指定CmakeLists.txt文件，根据注释进行相应添加

# CMakeLists.txt
# 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.
#CMakeLists.txt
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.
add_library(# 设置so文件名称.Hello# 设置这个so文件为共享.SHARED# Provides a relative path to your source file(s).src/main/jni/Hello.c)
add_library(# 设置so文件名称.Test# 设置这个so文件为共享.SHARED# Provides a relative path to your source file(s).src/main/jni/Test.c)
add_library(# 设置so文件名称.CCallJava# 设置这个so文件为共享.SHARED# Provides a relative path to your source file(s).src/main/jni/CCallJava.c)# 添加 log 库的链接
target_link_libraries(CCallJava log)
target_link_libraries(Test log)# 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.# 制定目标库.Hello# Links the target library to the log library# included in the NDK.${log-lib} )

第四步，首先进行Java代码C代码的操作
1.JNI2.java代码如下

/*** @Author: ly* @Date: 2023/8/6* @Description: java调C代码*/
public class JNI2 {static {System.loadLibrary("Test"); //加载动态链接库}/*** 让C代码做加法运算,把结果返回* 场景：大量运算，编解码之类的，需要性能很高的情况下，可以用C代码** @param x* @param y* @return*/public native int add(int x, int y);/*** 从java传入字符串，C代码进行拼接** @param s I am from java* @return I am from java and I am from c*/public native String sayHello(String s);/*** 让C代码给每个元素都加上10** @param intArray* @return*/public native int[] increaseArrayEles(int[] intArray);/*** 应用：检查密码是否正确，如果正确返回200，否则返回400** @param pwd* @return*/public native int checkPwd(String pwd);
}

2.根据命令行javah +JNI2的全类名，生成Test.c对应的C代码头文件com_example_jniproject_JNI2.h

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_example_jniproject_JNI2 */#ifndef _Included_com_example_jniproject_JNI2
#define _Included_com_example_jniproject_JNI2
#ifdef __cplusplus
extern "C" {
#endif
/** Class:     com_example_jniproject_JNI2* Method:    add* Signature: (II)I*/
JNIEXPORT jint JNICALL Java_com_example_jniproject_JNI2_add(JNIEnv *, jobject, jint, jint);/** Class:     com_example_jniproject_JNI2* Method:    sayHello* Signature: (Ljava/lang/String;)Ljava/lang/String;*/
JNIEXPORT jstring JNICALL Java_com_example_jniproject_JNI2_sayHello(JNIEnv *, jobject, jstring);/** Class:     com_example_jniproject_JNI2* Method:    increaseArrayEles* Signature: ([I)[I*/
JNIEXPORT jintArray JNICALL Java_com_example_jniproject_JNI2_increaseArrayEles(JNIEnv *, jobject, jintArray);/** Class:     com_example_jniproject_JNI2* Method:    checkPwd* Signature: (Ljava/lang/String;)I*/
JNIEXPORT jint JNICALL Java_com_example_jniproject_JNI2_checkPwd(JNIEnv *, jobject, jstring);#ifdef __cplusplus
}
#endif
#endif

3.根据jni协议，去写对应的c代码，创建Test.c文件，代码如下

//
// Created by DELL on 2023/8/6.
//
#include "com_example_jniproject_JNI2.h"
#include "string.h"
#include <stdlib.h>#include <android/log.h>#define TAG "luyu"
#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG,TAG ,__VA_ARGS__) // 定义LOGD类型
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO,TAG ,__VA_ARGS__) // 定义LOGI类型
#define LOGW(...) __android_log_print(ANDROID_LOG_WARN,TAG ,__VA_ARGS__) // 定义LOGW类型
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR,TAG ,__VA_ARGS__) // 定义LOGE类型
#define LOGF(...) __android_log_print(ANDROID_LOG_FATAL,TAG ,__VA_ARGS__) // 定义LOGF类型JNIEXPORT char *JNICALL Java_com_example_MyClass_myMethod(JNIEnv *env, jobject obj, jstring jstr) {const char *cstr = (*env)->GetStringUTFChars(env, jstr, NULL);// 使用 cstr 进行操作，并获取结果（假设结果为 result）(*env)->ReleaseStringUTFChars(env, jstr, cstr);char *result = (char *) malloc(strlen(cstr) + 1);strcpy(result, cstr);return result;
}/*** jint:返回值* Java_全类名_方法名* JNIEnv *env*/
jint Java_com_example_jniproject_JNI2_add(JNIEnv *env, jobject jobj, jint ji, jint jj) {int result = ji + jj;return result;
};/*** 从java传入字符串，C代码进行拼接** @param s I am from java* @return I am from java and I am from c
*/jstring Java_com_example_jniproject_JNI2_sayHello(JNIEnv *env, jobject jobj, jstring jstring1) {char *fromJava = Java_com_example_MyClass_myMethod(env, jobj, jstring1);char *fromC = " and I am from C";//拼接函数，拼接后得到的结果放到第一个参数里面strcat(fromJava, fromC);//把拼接的结果放在第一个参数里面//jstring     (*NewStringUTF)(JNIEnv*, const char*);LOGE("fromJava==%s\n", fromJava);return (*env)->NewStringUTF(env, fromJava);
};/*** 给每个元素加10* 场景：图片处理，颜色矩阵(就是数组)，进行数组的处理*/
jintArray Java_com_example_jniproject_JNI2_increaseArrayEles(JNIEnv *env, jobject jobj, jintArray jintArray1) {//1.得到数组的长度//jsize       (*GetArrayLength)(JNIEnv*, jarray);jsize size = (*env)->GetArrayLength(env, jintArray1);//2.得到数组的元素// jint*       (*GetIntArrayElements)(JNIEnv*, jintArray, jboolean*);jint *intArray = (*env)->GetIntArrayElements(env, jintArray1,JNI_FALSE);//这里传0 false表示 在同一份内存操作，不开辟新的内存//3.遍历数组，给每个元素加10int i;for (i = 0; i < size; i++) {*(intArray + i) += 10;}// 4. 同步修改到 Java 层(*env)->ReleaseIntArrayElements(env, jintArray1, intArray, 0);//4.返回结果return jintArray1;
};/*** 应用：检查密码是否正确，如果正确返回200，否则返回400*/
jint Java_com_example_jniproject_JNI2_checkPwd(JNIEnv *env, jobject jobj, jstring jstring1) {//假设服务器的密码是123456char *origin = "123456";char *fromUser = Java_com_example_MyClass_myMethod(env, jobj, jstring1);//函数比较字符串是否相同int code = strcmp(origin, fromUser);LOGE("code==%d\n", code);if (code == 0) {return 200;} else {return 400;}
};

第五步，C代码调用Java代码，首先创建JNI3.java

/*** @Author: ly* @Date: 2023/8/6* @Description: C代码调用Java代码*/
public class JNI3 {static {System.loadLibrary("CCallJava"); //加载动态链接库}//当执行这个方法的时候，让C代码调用//public int add(int x, int y)public native void callbackAdd();/*** 当执行这个方法的时候，让C代码调用* public void helloFromJava()*/public native void callbackHelloFromJava();/*** 当执行这个方法的时候，让C代码调用* public void printString(String s)*/public native void callbackPrintString();/*** 当执行这个方法的时候，让C代码调用* public static void sayHello(String s)*/public native void callbackSayHello();public int add(int x, int y) {Log.e("TAG", "add()  x=" + x + " y=" + y);return x + y;}public void helloFromJava() {Log.e("TAG", "helloFromJava");}public void printString(String s) {Log.e("TAG", "C中输入的：" + s);}public static void sayHello(String s) {Log.e("TAG", "我是java代码中的JNI" +".java中的sayHello(String s)静态方法,我被C调用了：" + s);}
}

2.根据命令行，javah +JNI3全类名，生成CCallJava.c对应的头文件
com_example_jniproject_JNI3.h

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_example_jniproject_JNI3 */#ifndef _Included_com_example_jniproject_JNI3
#define _Included_com_example_jniproject_JNI3
#ifdef __cplusplus
extern "C" {
#endif
/** Class:     com_example_jniproject_JNI3* Method:    callbackAdd* Signature: ()V*/
JNIEXPORT void JNICALL Java_com_example_jniproject_JNI3_callbackAdd(JNIEnv *, jobject);/** Class:     com_example_jniproject_JNI3* Method:    callbackHelloFromJava* Signature: ()V*/
JNIEXPORT void JNICALL Java_com_example_jniproject_JNI3_callbackHelloFromJava(JNIEnv *, jobject);/** Class:     com_example_jniproject_JNI3* Method:    callbackPrintString* Signature: ()V*/
JNIEXPORT void JNICALL Java_com_example_jniproject_JNI3_callbackPrintString(JNIEnv *, jobject);/** Class:     com_example_jniproject_JNI3* Method:    callbackSayHello* Signature: ()V*/
JNIEXPORT void JNICALL Java_com_example_jniproject_JNI3_callbackSayHello(JNIEnv *, jobject);#ifdef __cplusplus
}
#endif
#endif

3.对应的CCallJava.c文件中的代码如下

//
// Created by DELL on 2023/8/6.
//
#include "com_example_jniproject_JNI3.h"
#include <stdlib.h>
#include <stdio.h>#include <android/log.h>#define TAG "luyu"
#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG,TAG ,__VA_ARGS__) // 定义LOGD类型
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO,TAG ,__VA_ARGS__) // 定义LOGI类型
#define LOGW(...) __android_log_print(ANDROID_LOG_WARN,TAG ,__VA_ARGS__) // 定义LOGW类型
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR,TAG ,__VA_ARGS__) // 定义LOGE类型
#define LOGF(...) __android_log_print(ANDROID_LOG_FATAL,TAG ,__VA_ARGS__) // 定义LOGF类型/*** 让C代码调用Java中JNI类的public int add(int x ,int y)*/
JNIEXPORT void Java_com_example_jniproject_JNI3_callbackAdd(JNIEnv *env, jobject jobj) {//1.得到字节码//jclass      (*FindClass)(JNIEnv*, const char*);jclass jclazz = (*env)->FindClass(env, "com/example/jniproject/JNI3");//2.得到方法//jmethodID   (*GetMethodID)(JNIEnv*, jclass, const char*, const char*);//最后一个参数是方法签名jmethodID jmethodId = (*env)->GetMethodID(env, jclazz, "add", "(II)I");//3.实例化该类jobject jobject1 = (*env)->AllocObject(env, jclazz);//4.调用方法//jint        (*CallIntMethod)(JNIEnv*, jobject, jmethodID, ...);jint value = (*env)->CallIntMethod(env, jobject1, jmethodId, 99, 1);//成功调用LOGE("value==%d\n", value);
};/**** 让C代码调用* public void helloFromJava()*/
JNIEXPORT void JNICALL Java_com_example_jniproject_JNI3_callbackHelloFromJava(JNIEnv *env, jobject jobj) {//1.得到字节码//jclass      (*FindClass)(JNIEnv*, const char*);jclass jclazz = (*env)->FindClass(env, "com/example/jniproject/JNI3");//2.得到方法//jmethodID   (*GetMethodID)(JNIEnv*, jclass, const char*, const char*);//最后一个参数是方法签名jmethodID jmethodIds = (*env)->GetMethodID(env, jclazz, "helloFromJava", "()V");//3.实例化该类jobject jobject1 = (*env)->AllocObject(env, jclazz);//4.调用方法//jint        (*CallIntMethod)(JNIEnv*, jobject, jmethodID, ...);(*env)->CallVoidMethod(env, jobject1, jmethodIds);
};/**** 让C代码调用* public void printString(String s)**/
JNIEXPORT void JNICALL Java_com_example_jniproject_JNI3_callbackPrintString(JNIEnv *env, jobject jobj) {//1.得到字节码//jclass      (*FindClass)(JNIEnv*, const char*);jclass jclazz = (*env)->FindClass(env, "com/example/jniproject/JNI3");//2.得到方法//jmethodID   (*GetMethodID)(JNIEnv*, jclass, const char*, const char*);//最后一个参数是方法签名jmethodID jmethodIds = (*env)->GetMethodID(env, jclazz, "printString", "(Ljava/lang/String;)V");//3.实例化该类jobject jobject1 = (*env)->AllocObject(env, jclazz);//4.调用方法//jint        (*CallIntMethod)(JNIEnv*, jobject, jmethodID, ...);// jstring     (*NewStringUTF)(JNIEnv*, const char*);jstring jst = (**env).NewStringUTF(env, "I am Android!");(*env)->CallVoidMethod(env, jobject1, jmethodIds, jst);
};/*** 让C代码调用* public static void sayHello(String s)**/
JNIEXPORT void JNICALL Java_com_example_jniproject_JNI3_callbackSayHello(JNIEnv *env, jobject jobj){//1.得到字节码//jclass      (*FindClass)(JNIEnv*, const char*);jclass jclazz = (*env)->FindClass(env, "com/example/jniproject/JNI3");//2.得到方法// jmethodID   (*GetStaticMethodID)(JNIEnv*, jclass, const char*, const char*);//最后一个参数是方法签名jmethodID jmethodIds = (*env)->GetStaticMethodID(env, jclazz, "sayHello", "(Ljava/lang/String;)V");jstring jst = (**env).NewStringUTF(env, "I am Android!");(*env)->CallStaticVoidMethod(env,jclazz,jmethodIds,jst);
};

之后，在MainActivity中调用对应的方法即可

public class MainActivity extends AppCompatActivity {private JNI2 jin2;private static final String TAG = "MainActivity";private JNI3 mJNI3;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);jin2 = new JNI2();mJNI3 = new JNI3();}/******以下是Java代码调用C*****/public void checkPwd(View view) {int result = jin2.checkPwd("12345678");Log.i(TAG, "result==" + result);}public void increaseArrayEles(View view) {int array[] = {1, 2, 3, 4};jin2.increaseArrayEles(array);for (int i = 0; i < array.length; i++) {Log.i(TAG, "result[" + i + "]:" + array[i]);}}public void sayHello(View view) {String result = jin2.sayHello("I am from java");Log.i(TAG, "result==" + result);}public void add(View view) {int result = jin2.add(99, 1);Log.i(TAG, "result==" + result);}/******以下是C调Java代码*****/public void callbackAdd(View view) {mJNI3.callbackAdd();}public void callbackHelloFromJava(View view) {mJNI3.callbackHelloFromJava();}public void callbackPrintString(View view) {mJNI3.callbackPrintString();}public void callbackSayHello(View view) {mJNI3.callbackSayHello();}
}

点击按钮便可输出对应的日志，表示调用成功。