【系統移植】JNI

jni代碼

java調用jni的接口:

1, 調用動態庫

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

2, 調用驅動方法名:
    public native int openDev();
  
3, 直接去調用,不須要去實現openDev()

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

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

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

1, JNI_OnLoad()    < == System.loadLibrary( "led_jni") 第一個函數
  |
 原型 :jint JNI_OnLoad(JavaVM * vm, void * reserved)
  返回值 : 正確 : JNI_VERSION_1_4
   錯誤 : 小於 0;
 a, 獲取jni的版本,和dvm的運行環境對象 env (提供操做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 :
    正確 : JNI_OK == 0
    錯誤 : 小於 0
   
 b, 構建映射表, 註冊給dvm
  表示映射表 :
   typedef struct { 
       const char * name;    // java方法名
       const char * signature;   // 方法的參數和返回值 描述
       void *       fnPtr; // c/c++的函數名
  } 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},
  };

  註冊 :
   env - >RegisterNatives(jclass clazz, const JNINativeMethod * methods,jint nMethods)
   參數 1 : 將native方法所在的包.類轉換成jclass, 告訴dvm,本地方法是屬於哪一個類
   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

#指定鏈接動態庫 < 相似於gcc   -lxx
LOCAL_SHARED_LIBRARIES : = \
        libcutils
#指定頭文件路徑, 相似於gcc -Ixxx
LOCAL_C_INCLUDES += \
        $(JNI_H_INCLUDE)
#編譯成so,須要一個標誌
LOCAL_PRELINK_MODULE : = false
include $(BUILD_SHARED_LIBRARY)

編譯:

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 :進入目錄 '/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 :離開目錄「 /home /ldswfun /src_s5pc /eclair_2. 1_farsight」

運行:

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

 

 @成鵬致遠

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