学步园

jbytearray转c++byte数组 

jbyte * arrayBody = env->GetByteArrayElements(data,0); 
jsize theArrayLengthJ = env->GetArrayLength(data); 
BYTE * starter = (BYTE *)arrayBody; 

jbyteArray 转 c++中的BYTE[] 

//jbytearray strIn
jbyte * olddata = (jbyte*)env->GetByteArrayElements(strIn, 0);
jsize  oldsize = env->GetArrayLength(strIn);
BYTE* bytearr = (BYTE*)olddata;
int len = (int)oldsize;

C++中的BYTE[]转jbyteArray 

//nOutSize是BYTE数组的长度 BYTE pData[]
jbyte *by = (jbyte*)pData;
jbyteArray jarray = env->NewByteArray(nOutSize);
env->SetByteArrayRegin(jarray, 0, nOutSize, by);

jbyteArray 转 char * 

char* data = (char*)env->GetByteArrayElements(strIn, 0);

char* 转jstring

jstring WindowsTojstring(JNIEnv* env, char* str_tmp)
{
 jstring rtn=0;
 int slen = (int)strlen(str_tmp);
 unsigned short* buffer=0;
 if(slen == 0)
 {
  rtn = env->NewStringUTF(str_tmp);
 }
 else
 {
  int length = MultiByteToWideChar(CP_ACP, 0, (LPCSTR)str_tmp, slen, NULL, 0);
  buffer = (unsigned short*)malloc(length*2+1);
  if(MultiByteToWideChar(CP_ACP, 0, (LPCSTR)str_tmp, slen, (LPWSTR)buffer, length) > 0)
  {
   rtn = env->NewString((jchar*)buffer, length);
  }
 }
 if(buffer)
 {
  free(buffer);
 }
 return rtn;
}

char* jstring互转

JNIEXPORT jstring JNICALL Java_com_explorer_jni_SambaTreeNative_getDetailsBy
  (JNIEnv *env, jobject jobj, jstring pc_server, jstring server_user, jstring server_passwd)
{
	const char *pc = env->GetStringUTFChars(pc_server, NULL);
	const char *user = env->GetStringUTFChars(server_user, NULL);
	const char *passwd = env->GetStringUTFChars(server_passwd, NULL);
	const char *details = smbtree::getPara(pc, user, passwd);
	jstring jDetails = env->NewStringUTF(details);
	return jDetails;
}

4. JNI开发中碰到的"error: request for member 'GetStringUTFChars' in something not a structure or union"

strTemp=env->GetStringUTFChars(env,str,NULL);   这句不能这么写
 
C语言里要写成   strTemp=（*env)->GetStringUTFChars(env,str,NULL);  
C++里 要这么写  strTemp= env->GetStringUTFChars(str,NULL);  
 
这个还不是jni最难的，我认为JNI最难的是 数组类型参数值的传递（java传给C++或C++传给java），尤其是字符串数组传递。得动态开辟空间，传递后内存释放问题更闹心，搞不清哪个变量归java管不用释放，哪个归C++管需要手动释放。