JNI文件添加

JNI文件夹中一般包括Android.mk、native.cpp和其他.c/.h文件

Android.mk文件

LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)

#LOCAL_MODULE_TAGS := eng samples
LOCAL_MODULE_TAGS := optional

# This is the target being built.
LOCAL_MODULE:= libamtjni #这里是JNI库名，lib+名字+jni

# All of the source files that we will compile.
LOCAL_SRC_FILES:= \   #所要编译的源码 .c和.cpp文件
  native.cpp \
  amt_command.c

# All of the shared libraries we link against.
LOCAL_SHARED_LIBRARIES := \  #需要连接的共享库										libutils

# No static libraries.
LOCAL_STATIC_LIBRARIES :=

# Also need the JNI headers.
LOCAL_C_INCLUDES += \
	$(JNI_H_INCLUDE)

# No special compiler flags.
LOCAL_CFLAGS +=

# Don't prelink this library.  For more efficient code, you may want
# to add this library to the prelink map and set this to true. However,
# it's difficult to do this for applications that are not supplied as
# part of a system image.

LOCAL_PRELINK_MODULE := false

include $(BUILD_SHARED_LIBRARY)

native.cpp文件

#include <utils/Log.h>
#include <stdio.h>
#include "jni.h"

#include <stdlib.h>
#define LOGD  ALOGD
#define LOGE  ALOGE
#define LOGI  ALOGI

static jstring                 										          app_test(JNIEnv *env, jobject thiz) 											    {													             FILE *fp = NULL;									                                    char serial_no_buffer_a[100 + 1];									                  char *usb_serial_no_file_path = "/amt/usb_serial";								         memset( serial_no_buffer_a, 0, sizeof(serial_no_buffer_a) );								  fp = fopen(usb_serial_no_file_path, "r");
   if(NULL != fp)
   {
  //if( EOF != fscanf(fp, "%s", serial_no_buffer_a))
   fread( serial_no_buffer_a, sizeof(serial_no_buffer_a) - 1,  1,  fp );							   if( feof(fp) )
     {
       LOGI( "Settings status read adb serial no ok and content is %s", serial_no_buffer_a  );         
      }
       else
      {
       LOGI("Settings status read fread error or file content length bigger then 100" );
       }
  
      fclose(fp);
    }
    else
    {
    LOGI("Settings status read fopen error or usb serial file not exist" );
    LOGI("Settings status return default serial no T802");
    strcpy( serial_no_buffer_a, "T802" );
   }													        return env->NewStringUTF( serial_no_buffer_a );
}                                                                                                                             static const char *classPathName = "com/android/settings/deviceinfo/Native";                                                       static JNINativeMethod methods[] = {
 
   {"uni_serial_no_read", "()Ljava/lang/String;", (void*)uni_serial_no_read },					             {"java文件中调用的函数名","(JNI函数参数类型)JNI函数返回值类型",(void*)jni函数名}
};														   /*
 * Register several native methods for one class.
 */
static int registerNativeMethods(JNIEnv* env, const char* className,
    JNINativeMethod* gMethods, int numMethods)
{
    jclass clazz;												        clazz = env->FindClass(className);
    if (clazz == NULL) {
        LOGE("Native registration unable to find class '%s'", className);
        return JNI_FALSE;
    }
    if (env->RegisterNatives(clazz, gMethods, numMethods) < 0) {
        LOGE("RegisterNatives failed for '%s'", className);
        return JNI_FALSE;
    }													       return JNI_TRUE;
}
/*
 * Register native methods for all classes we know about.
 *
 * returns JNI_TRUE on success.
 */
static int registerNatives(JNIEnv* env)
{
  if (!registerNativeMethods(env, classPathName,
                 methods, sizeof(methods) / sizeof(methods[0]))) {
    return JNI_FALSE;
  }														return JNI_TRUE;
}/*
 * This is called by the VM when the shared library is first loaded.
 */
 
typedef union {
    JNIEnv* env;
    void* venv;
} UnionJNIEnvToVoid;											         jint JNI_OnLoad(JavaVM* vm, void* reserved)
{
    UnionJNIEnvToVoid uenv;
    uenv.venv = NULL;
    jint result = -1;
    JNIEnv* env = NULL;
    
    LOGI("JNI_OnLoad");											           if (vm->GetEnv(&uenv.venv, JNI_VERSION_1_4) != JNI_OK) {
        LOGE("ERROR: GetEnv failed");
        goto bail;
    }
    env = uenv.env;											           if (registerNatives(env) != JNI_TRUE) {
        LOGE("ERROR: registerNatives failed");
        goto bail;
    }
    
    result = JNI_VERSION_1_4;
    
bail:
    return result;
}

 

在java文件中，如果调用JNI的地方比较少，可以直接在调用的文件中加入

class Native {     static {           System.loadLibrary("编译的jni库名-lib");#如：编译的出来的名字叫 libtestjni ，此处名字为testjni    }

 static native JNI库中java的函数名；

}

如果需要很多文件调用或JNI文件中函数比较多，可以在java文件中新创建一个Native.java

package 包名;

public class Native {
    static {
        // The runtime will add "lib" on the front and ".o" on the end of
        // the name supplied to loadLibrary.
        System.loadLibrary("amtjni");
    }

    static native int add(int a, int b);									       static native 返回值类型 函数名（参数）；#此处的函数名要和Native.cpp中的JNINativeMethod methods[]第一列函数名一致；
    }

在其他java文件中就可以直接以Native.函数名 来调用