【系统移植】JNI-白红宇

【系统移植】JNI

阅读量：5966 次

发布时间：2019-06-19

本文共 3064 字，大约阅读时间需要 10 分钟。

jni代码

java调用jni的接口:

1, 调用动态库

static{ 
  System.loadLibrary( 
"led_jni");   
// system/lib/libled_jni.so
 } 

2, 调用驱动方法名:

public native int openDev();

3, 直接去调用,不需要去实现openDev()

     openDev(); 
public native 
int openDev(); 
public native 
int DevOn(); 
public native 
int DevOff(); 
public native 
int closeDev(); 

jni的接口代码: jni代码(*.cpp)==>libled_jni.so

参考模板:Native.cpp development\samples\simplejni\Jni 2599 2011-5-17

1, JNI_OnLoad()    
<
== System.loadLibrary( 
"led_jni") 第一个函数 
|
 原型 
:jint JNI_OnLoad(JavaVM 
* vm, 
void
* reserved) 
  返回值 
: 正确 
: JNI_VERSION_1_4 
   错误 
: 小于 
0; 
 a, 获取jni的版本,和dvm的运行环境对象 env (提供操作jni的方法) 
  原型 
:  jint GetEnv( 
void
*
* env, jint version) 
  使用 
:
    JNIEnv 
* env 
= NULL; 
   vm 
-
>GetEnv(( 
void
*
*) 
&env, JNI_VERSION_1_4)  
   返回值 
:
    正确 
: JNI_OK 
==
0
    错误 
: 小于 
0
 b, 构建映射表, 注册给dvm 
  表示映射表 
:
typedef
struct {  
const
char
* name;    
// java方法名
const
char
* signature;   
// 方法的参数和返回值 描述
void
*       fnPtr; 
// c/c++的函数名
  } JNINativeMethod; 
const
static JNINativeMethod   myMethods[] 
={ 
   { 
"openDev", 
"()I", ( 
void
*)open_led}, 
   { 
"DevOn", 
"()I",   ( 
void
*)led_on}, 
   { 
"DevOff", 
"()I",  ( 
void
*)led_off}, 
   { 
"closeDev", 
"()I", ( 
void
*)close_led}, 
  }; 
  注册 
:
   env 
-
>RegisterNatives(jclass clazz, 
const JNINativeMethod 
* methods,jint nMethods) 
   参数 
1
: 将native方法所在的包.类转换成jclass, 告诉dvm,本地方法是属于哪个类 
   jclass  myclz 
= env 
-
>FindClass( 
"com/hq/ledjnitest/LedActivity"); 
   env 
-
>RegisterNatives(myclz, myMethods,    
sizeof(myMethods) 
/
sizeof(myMethods[ 
0])); 

Android.mk

     LOCAL_PATH 
:
= $(call my 
-dir) 
include $(CLEAR_VARS) 
LOCAL_SRC_FILES 
:
= led_jni.cpp 
LOCAL_MODULE 
:
=libled_jni 
#指定连接动态库 
< 类似于gcc   
-lxx 
LOCAL_SHARED_LIBRARIES 
:
= \ 
        libcutils 
#指定头文件路径, 类似于gcc 
-Ixxx 
LOCAL_C_INCLUDES 
+= \ 
        $(JNI_H_INCLUDE) 
#编译成so,需要一个标志 
LOCAL_PRELINK_MODULE 
:
=
false
include $(BUILD_SHARED_LIBRARY) 

编译:

mmm mytest/jni/
==
==
==
==
==
==
==
==
==
==
==
==
==
==
==
==
==
==
==
==
==
==
PLATFORM_VERSION_CODENAME 
=REL 
PLATFORM_VERSION 
=
2. 
1
-update1 
TARGET_PRODUCT 
=fs100 
TARGET_BUILD_VARIANT 
=eng 
TARGET_SIMULATOR 
=
false
TARGET_BUILD_TYPE 
=release 
TARGET_ARCH 
=arm 
HOST_ARCH 
=x86 
HOST_OS 
=linux 
HOST_BUILD_TYPE 
=release 
BUILD_ID 
=ERE27 
==
==
==
==
==
==
==
==
==
==
==
==
==
==
==
==
==
==
==
==
==
==
make 
:进入目录 
'/home/ldswfun/src_s5pc/eclair_2.1_farsight'
target thumb C 
++
: libled_jni 
<
= mytest 
/jni 
/led_jni.cpp 
In file included from mytest 
/jni 
/led_jni.cpp 
:
5
:
dalvik 
/libnativehelper 
/
include
/nativehelper 
/jni.h 
:
489
: note 
: the mangling of 
'va_list' has changed in GCC 
4. 
4
target SharedLib 
: libled_jni (out 
/target 
/product 
/fs100 
/obj 
/SHARED_LIBRARIES 
/libled_jni_intermediates 
/LINKED 
/libled_jni.so) 
target Non 
-prelinked 
: libled_jni (out 
/target 
/product 
/fs100 
/symbols 
/system 
/lib 
/libled_jni.so) 
target Strip 
: libled_jni (out 
/target 
/product 
/fs100 
/obj 
/lib 
/libled_jni.so) 
Install 
: out 
/target 
/product 
/fs100 
/system 
/lib 
/libled_jni.so 
make 
:离开目录“ 
/home 
/ldswfun 
/src_s5pc 
/eclair_2. 
1_farsight” 

运行:

     apk 
==
=
>
/system 
/app 
so 
==
>
/syste 
/lib 
/
cp 
-raf out 
/target 
/product 
/fs100 
/system 
/lib 
/libled_jni.so    
/opt 
/myrootfs 
/system 
/lib 