public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        Button btn = new Button(this);
        btn.setText("测试ndk");
        btn.setOnClickListener(new ButtonOnClickListener());
        setContentView(btn);
        Toast.makeText(getApplicationContext(), PATH, Toast.LENGTH_LONG).show();
    }
    
    public final class ButtonOnClickListener implements OnClickListener{
     
  @Override
  public void onClick(View arg0) {
   // TODO Auto-generated method stub
   byte[] data = "zhanghongliu".getBytes();
   FileInputStream fis = null;
   FileOutputStream fos = null;
   int i = 0;
         for(i=1;i<=200000;i++){
    try {
     fis = new FileInputStream(RESOURCEPATH);
     int size = fis.available();
     data = new byte[size];
     fis.read(data, 0, size);
     String result = FileJNILib.videoCrypt(data,ENCRYPTPATH);
     Toast.makeText(getApplicationContext(), result, Toast.LENGTH_LONG).show();
     
           data = FileJNILib.videoDerypt(ENCRYPTPATH);
           fos = new FileOutputStream(DECRYPTPATH);
           fos.write(data);
    } catch (FileNotFoundException e) {
     // TODO Auto-generated catch block
     e.printStackTrace();
    } catch (IOException e) {
     // TODO Auto-generated catch block
     e.printStackTrace();
    }finally{
     try {
      if(null != fis){
       fis.close();
      }
      if(null != fos){
       fos.close();
      }
      data = null;
     } catch (IOException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
     }
    }
          Log.i("count", i+"");
          //data = null;
         }
         //Toast.makeText(getApplicationContext(), new String(data), Toast.LENGTH_LONG).show();
      //show();
  }
  
  public void show(){
   File newfile = new File(PATH);
         FileInputStream inStream = null;
   try {
    inStream = new FileInputStream(newfile);
   } catch (FileNotFoundException e) {
    // TODO Auto-generated catch block
    //e.printStackTrace();
   }
         String content = FileUtil.readInStream(inStream);
         Log.i("FileText", content);
         Toast.makeText(getApplicationContext(), content, Toast.LENGTH_LONG).show();
  }
     
    }

public static String readInStream(FileInputStream inStream){
  try {
   ByteArrayOutputStream outStream = new ByteArrayOutputStream();
   byte[] buffer = new byte[1024];
   int length = -1;
   while((length = inStream.read(buffer)) != -1 ){
    outStream.write(buffer, 0, length);
   }
   outStream.close();
   inStream.close();
   return outStream.toString();
  } catch (IOException e) {
   Log.i(TAG, e.getMessage());
  }
  return null;
 }

public class FileJNILib {
 
 static {
        System.loadLibrary("filejni");
    }
    public static native String videoCrypt(byte[] content, String dest_file);
    public static native byte[] videoDerypt(String dest_file);

public static native String videoDerypt(String dest_file, ByteArrayOutputStream outputstream);
    
}

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <sys/stat.h>

#include <jni.h> //jni的主要头文件

#include <android/log.h>
#define LOG_TAG "JNI"
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)
/* Header for class com_test_jni_FileJNILib */

/*
 * Class:     com_test_jni_FileJNILib
 * Method:    videoCrypt
 * Signature: ([BLjava/lang/String;)V
 */
JNIEXPORT jstring JNICALL videoCrypt
  (JNIEnv * env, jclass thiz, jbyteArray content, jstring dest_file){
  //env->GetStringUTFChars(source,NULL);

const char *path = (*env)->GetStringUTFChars(env, dest_file, NULL);
  LOGI(path);

FILE *fp = fopen(path,"wb");
  if(fp==NULL){
   LOGI("fopen error");
   (*env)->ReleaseStringUTFChars(env,dest_file, path);
   return (*env)->NewStringUTF(env, "fopen error");
  }
  char *data = (*env)->GetByteArrayElements(env,content, 0);
  int size = (*env)->GetArrayLength(env,content);
  //int iLen = sizeof(data);//C语言中判断数据类型或者表达式长度符
  LOGI("file size is %d", size);

crypt(data,size);

/******文件写入方法***********/
  //fputc('c',fp);
  //fputs(data,fp);
  fwrite(data,size,1,fp);
  //fprintf(fp,"%s",data);
  /*****************/

fclose(fp);
  (*env)->ReleaseByteArrayElements(env,content,data,0);
  (*env)->ReleaseStringUTFChars(env,dest_file, path);
  LOGI("execute complete");
  return (*env)->NewStringUTF(env, "encrypt successful");
}

/*
 * Class:     com_test_jni_FileJNILib
 * Method:    videoDerypt
 * Signature: (Ljava/lang/String;)[B
 */
JNIEXPORT jbyteArray JNICALL videoDerypt
  (JNIEnv * env, jclass thiz, jstring dest_file){
   const char *path = (*env)->GetStringUTFChars(env, dest_file, NULL);
   LOGI(path);

/*****得到文件长度*******/
   int size;
   struct stat  tFileStat;
   if( stat(path, &tFileStat ) )
   {
    LOGI("file not found error");
    (*env)->ReleaseStringUTFChars(env,dest_file, path);
    return NULL;
   }
   size=tFileStat.st_size;
   LOGI("file size is %d",size);//报错 int
   /************/

/*****分配内存*******/
   char *temp = NULL;
   temp=(char*)malloc(size);
   if(temp == NULL)
   {
    LOGI("malloc error");
    (*env)->ReleaseStringUTFChars(env,dest_file, path);
    return NULL;
   }
   // memset(temp,0x00,size*sizeof(char)+1);//初始化内存
   /************/

FILE *fp = fopen(path,"rb");
   if(fp==NULL){
    LOGI("fopen error");
    (*env)->ReleaseStringUTFChars(env,dest_file, path);
    free(temp);//释放内存
    temp=NULL;
    return NULL;
   }

/******文件读方法***********/
   //fgetc(fp);
   //fgets(temp,100,fp);
   fread(temp,size,1,fp);
   //fscanf(fp,"%s",temp);
   /*****************/

fclose(fp);

crypt(temp,size);

jbyteArray jarrRV =(*env)->NewByteArray(env,size);
   jbyte *jby =(*env)->GetByteArrayElements(env,jarrRV, 0);
   memcpy(jby, temp, size);//复制数据
   (*env)->SetByteArrayRegion(env,jarrRV, 0,size, jby);//将Jbyte 转换为jbarray数组
   (*env)->ReleaseByteArrayElements(env,jarrRV,jby,0);//释放jby数组* 解决长时间运行退出问题 内部引用超过指定数量
   //(*env)->DeleteLocalRef(env,jarrRV);//影响程序
   //(*env)->DeleteLocalRef(env,temp);//不对  一般用malloc申请内存，free释放
   free(temp);
   temp=NULL;
   (*env)->ReleaseStringUTFChars(env,dest_file, path);
   LOGI("execute complete");
   return jarrRV;
}

void crypt(char *data, int size){
 int i;
 char sPwd[]="************************";
    int pwdLen = sizeof(sPwd);
    //LOGI("dongao.com mobile_encrypt %d",pwdLen);
 int count=0;
 for(i=0; i<size; i++)
 {
            if(count >= pwdLen) count = 0;
   data[i]=data[i]^sPwd[count++];
   //LOGI("%c",sPwd[count >= 10 ?count=0:count++]);
 }
}

/*
 * Class:     com_test_jni_FileJNILib
 * Method:    videoDerypt
 * Signature: (Ljava/lang/String;Ljava/io/ByteArrayOutputStream;)V
 */
JNIEXPORT jstring JNICALL videoDerypt2ByteArray
  (JNIEnv * env, jclass thiz, jstring dest_file, jobject outputstream){
 return NULL;
}

static const JNINativeMethod gMethods[] = { //定义批量注册的数组，是注册的关键部分
{"videoCrypt", "([BLjava/lang/String;)Ljava/lang/String;", (void*)videoCrypt} ,// func2是在java中声明的native函数名，"()V"是函数的签名，可以通过javah获取。
{"videoDerypt", "(Ljava/lang/String;)[B", (void*)videoDerypt},
{"videoDerypt", "(Ljava/lang/String;Ljava/io/ByteArrayOutputStream;)Ljava/lang/String;", (void*)videoDerypt2ByteArray}
};

JNIEXPORT jint JNI_OnLoad(JavaVM* vm, void *reserved) //这是JNI_OnLoad的声明，必须按照这样的方式声明

{

JNIEnv* env = NULL; //注册时在JNIEnv中实现的，所以必须首先获取它

jint result = -1;

if((*vm)->GetEnv(vm, (void**)&env, JNI_VERSION_1_4) != JNI_OK) //从JavaVM获取JNIEnv，一般使用1.4的版本

return -1;

jclass clazz;

static const char* const kClassName="com/test/jni/FileJNILib";

clazz = (*env)->FindClass(env, kClassName); //这里可以找到要注册的类，前提是这个类已经加载到java虚拟机中。 这里说明，动态库和有native方法的类之间，没有任何对应关系。

if(clazz == NULL)

{

LOGI("cannot get class:%s\n", kClassName);

return -1;

}

if((*env)->RegisterNatives(env, clazz,gMethods, sizeof(gMethods)/sizeof(gMethods[0]))!= JNI_OK) //这里就是关键了，把本地函数和一个java类方法关联起来。不管之前是否关联过，一律把之前的替换掉！

{

LOGI("register native method failed!\n");

return -1;

}

return JNI_VERSION_1_4; //这里很重要，必须返回版本，否则加载会失败。

}

原文 http://blog.csdn.net/zhanghongliu1122/article/details/9411921