android 9.0 ndk,android9.0-ndk开发（2）-JNI代码-Go语言中文社区-优快云博客

注1：android9.0-ndk开发系列文档提供一个ndk编译JNI库，并访问第三方库，APP 直接通过jar接口调用的方法。

注2：本文为个人学习记录，可能存在个别或多处错误，欢迎指正和讨论。

android9.0-ndk开发(1)-第三方库的生成

android9.0-ndk开发(2)-JNI代码

android9.0-ndk开发(3)-Jar打包

android9.0-ndk开发(4)-APP 调用实例

一、创建java 接口代码

myjni.java

package com.sample.jnitest;

public class myjni {

public static native int SetString(String msg);

public static native String GetString();

//load library

static

{

System.loadLibrary("native_jni_test");

}

点击Make Project

会自动生成.class 文件：

C:UsersalexAndroidStudioProjectsjni_testappbuildintermediatesjavacdebugclassescomsamplejnitestmyjni.class

二、自动生成JNI头文件

创建jni文件夹

使用Android Stutio的Terminal 切换到jni目录

使用命令自动生成头文件：

javah -d . -classpath C:UsersalexAndroidStudioProjectsjnitestappbuildintermediatesjavacdebugclasses com.sample.jnitest.myjni

生成的头文件如下：

com_sample_jnitest_myjni.h

/* DO NOT EDIT THIS FILE - it is machine generated */

#include

/* Header for class com_sample_jnitest_myjni */

#ifndef _Included_com_sample_jnitest_myjni

#define _Included_com_sample_jnitest_myjni

#ifdef __cplusplus

extern "C" {

#endif

* Class: com_sample_jnitest_myjni

* Method: SetString

* Signature: (Ljava/lang/String;)I

JNIEXPORT jint JNICALL Java_com_sample_jnitest_myjni_SetString

(JNIEnv *, jclass, jstring);

* Class: com_sample_jnitest_myjni

* Method: GetString

* Signature: (Ljava/lang/String;)I

JNIEXPORT jint JNICALL Java_com_sample_jnitest_myjni_GetString

(JNIEnv *, jclass, jstring);

#ifdef __cplusplus

}

#endif

三、第三方库导入

在jni目录下新建thirdlibslibs

thirdlibsinclude 目录。

将(1)中生成的第三方库so库文件(包含ABI文件夹)复制到libs目录

将(1)中的sample.h文件(包含ABI文件夹)复制到libs目录

四、JNI代码实现

创建com_sample_jnitest_myjni.c

实现头文件定义的函数即可。

JNI代码实现方式二：采用RegisterNatives的方式注册到JVM

4.1 代码实现：

// Created by alex on 8/27/2019.

#include

#define JNI_CLASSIC

#ifdef JNI_CLASSIC

#include "com_sample_jnitest_myjni.h"

static jstring g_msg;

* Class: com_sample_jnitest_myjni

* Method: SetString

* Signature: (Ljava/lang/String;)I

JNIEXPORT jint JNICALL Java_com_sample_jnitest_myjni_SetString

(JNIEnv *env, jclass clazz, jstring msg)

{

__android_log_print(ANDROID_LOG_DEBUG,"myjni","Java_com_sample_jni_1test_myjni_SetString...");

__android_log_print(ANDROID_LOG_DEBUG,"myjni","%s ",msg);

g_msg = msg;

return 0;

}

* Class: com_sample_jnitest_myjni

* Method: GetString

* Signature: (Ljava/lang/String;)I

JNIEXPORT jint JNICALL Java_com_sample_jnitest_myjni_GetString

(JNIEnv *env, jclass clazz, jstring msg)

{

__android_log_print(ANDROID_LOG_DEBUG,"myjni","Java_com_sample_jni_1test_myjni_GetString...");

msg = g_msg;

return 0;

}

#else

static jstring g_msg;

* Class: com_sample_jnitest_myjni

* Method: SetString

* Signature: (Ljava/lang/String;)I

jint Java_com_sample_jnitest_myjni_SetString

(JNIEnv *env, jclass clazz, jstring msg)

{

__android_log_print(ANDROID_LOG_DEBUG,"myjni","Java_com_sample_jni_1test_myjni_SetString...");

__android_log_print(ANDROID_LOG_DEBUG,"myjni","%s ",msg);

g_msg = msg;

return 0;

}

* Class: com_sample_jnitest_myjni

* Method: GetString

* Signature: (Ljava/lang/String;)I

jint Java_com_sample_jnitest_myjni_GetString

(JNIEnv *env, jclass clazz, jstring msg)

{

__android_log_print(ANDROID_LOG_DEBUG,"myjni","Java_com_sample_jni_1test_myjni_GetString...");

msg = g_msg;

return 0;

}

static const JNINativeMethod methods[]={

{"Java_com_sample_jnitest_myjni_SetString","(Ljava/lang/String;)I",(void *)Java_com_sample_jnitest_myjni_SetString},

{"Java_com_sample_jnitest_myjni_GetString","(Ljava/lang/String;)I",(void *)Java_com_sample_jnitest_myjni_GetString},

};

JNIEXPORT jint JNICALL JNIOnLoad

(JavaVM *jvm, void *reserved)

{

__android_log_print(ANDROID_LOG_DEBUG,"JNITag","enter jni_onload");

JNIEnv* env = NULL;

jclass cls;

jint result=-1;

if( (*jvm)->GetEnv(jvm,(void**)&env , JNI_VERSION_1_6) != JNI_OK)

return JNI_ERR;

cls=(*env)->FindClass(env,"com/sample/jnitest/myjni");

if(cls == NULL)

return JNI_ERR;

if((*env)->RegisterNatives(env,cls,methods,sizeof(methods)/sizeof(methods[0]))<0){

return JNI_ERR;

}

return JNI_VERSION_1_6;

}

#endif

4.2 创建 Android.mk 和 Application.mk

在jni目录创建 Android.mk 和 Application.mk

创建Android.mk

LOCAL_PATH := $(call my-dir)

local_c_includes :=

$(LOCAL_PATH)

local_src_files:=

com_sample_jnitest_myjni.c

include $(CLEAR_VARS)

LOCAL_LDLIBS +=-llog -lz

LOCAL_MODULE :=native_jni_test

LOCAL_SRC_FILES += $(local_src_files)

LOCAL_C_INCLUDES += $(local_c_includes)

LOCAL_MODULE_TAGS := optional

include $(BUILD_SHARED_LIBRARY)

创建 Application.mk

LOCAL_PATH := $(call my-dir)

APP_STL :=c++_static

APP_CPPFLAGS := -frtti -fexceptions

APP_ABI :=all

APP_PLATFORM :=android-28

APP_BUILD_SCRIPT := $(LOCAL_PATH)/Android.mk

五、编译

在Android Studio使用编译命令：

ndk-build NDK_APPLICATION_MK=./Application.mk NDK_PROJECT_PATH=./

即可生产各硬件版本的库文件：

[arm64-v8a] Compile : native_jni_test <= com_sample_jnitest_myjni.c

[arm64-v8a] SharedLibrary : libnative_jni_test.so

[arm64-v8a] Install : libnative_jni_test.so => libs/arm64-v8a/libnative_jni_test.so

[x86_64] Compile : native_jni_test <= com_sample_jnitest_myjni.c

[x86_64] SharedLibrary : libnative_jni_test.so

[x86_64] Install : libnative_jni_test.so => libs/x86_64/libnative_jni_test.so

[armeabi-v7a] Compile thumb : native_jni_test <= com_sample_jnitest_myjni.c

[armeabi-v7a] SharedLibrary : libnative_jni_test.so

[armeabi-v7a] Install : libnative_jni_test.so => libs/armeabi-v7a/libnative_jni_test.so

[x86] Compile : native_jni_test <= com_sample_jnitest_myjni.c

[x86] SharedLibrary : libnative_jni_test.so

[x86] Install : libnative_jni_test.so => libs/x86/libnative_jni_test.so