JNI的某些数组和字符串类型转换

  JNI C C++ C# Windows

jbytearray转c++byte数组 

C代码   

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

jbyteArray 转 c++中的BYTE[] 

C代码   

 //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 

C代码   

 //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 * 

C代码   

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

char* 转jstring 

C代码   

 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;
 }

下面这个没有用过，刚看到，也写进来，以后如果遇到可以验证下看。 

jstring 转 char* 或者 const char* 

C代码   

 // jstring str
 const char *key = env->GetStringUTFChars(str, 0);
 //jboolean isOffer
 jsClient->modify(key, isOffer);
 env->ReleaseStringUTFChars(str, key);

JNI 返回 jbyteArray 

C代码   

 JNIEXPORT jbyteArray JNICALL Java_Test_getByteArray(JNIEnv *env, jobject obj)
 {
     jbyteArray firstMacArray = env->NewByteArray( 6 );
     ......
     jbyte *bytes = env->GetByteArrayElements( firstMacArray, 0);
     for ( int i = 0; i < sizeof( pAdapterInfo->Address ); i++ )
     {
        bytes[ i ] = pAdapterInfo->Address[ i ];
     }

     env->SetByteArrayRegion(firstMacArray, 0, 6, bytes );
     return firstMacArray;
 }

//jstring to char* 

C代码   

 char* jstringTostring(JNIEnv* env, jstring jstr)
 {
   char* rtn = NULL;
   jclass clsstring = env->FindClass("java/lang/String");
   jstring strencode = env->NewStringUTF("utf-8");
   jmethodID mid = env->GetMethodID(clsstring, "getBytes", "(Ljava/lang/String;)[B");
   jbyteArray barr= (jbyteArray)env->CallObjectMethod(jstr, mid, strencode);
   jsize alen = env->GetArrayLength(barr);
   jbyte* ba = env->GetByteArrayElements(barr, JNI_FALSE);
   if (alen > 0)
   {
     rtn = (char*)malloc(alen + 1);
     memcpy(rtn, ba, alen);
     rtn[alen] = 0;
   }
   env->ReleaseByteArrayElements(barr, ba, 0);
   return rtn;
 }

//char* to jstring 

C代码   

 jstring stoJstring(JNIEnv* env, const char* pat)
 {
 jclass strClass = env->FindClass("Ljava/lang/String;");
 jmethodID ctorID = env->GetMethodID(strClass, "<init>", "([BLjava/lang/String;)V");
 jbyteArray bytes = env->NewByteArray(strlen(pat));
 env->SetByteArrayRegion(bytes, 0, strlen(pat), (jbyte*)pat);
 jstring encoding = env->NewStringUTF("utf-8");
 return (jstring)env->NewObject(strClass, ctorID, bytes, encoding);
 }

//将jstring类型转换成windows类型 

C代码   

 char* jstringToWindows( JNIEnv *env, jstring jstr )
 {
 int length = (env)->GetStringLength(jstr );
 const jchar* jcstr = (env)->GetStringChars(jstr, 0 );
 char* rtn = (char*)malloc( length*2+1 );
 int size = 0;
 size = WideCharToMultiByte( CP_ACP, 0, (LPCWSTR)jcstr, length, rtn,(length*2+1), NULL, NULL );
 if( size <= 0 )
 return NULL;
 (env)->ReleaseStringChars(jstr, jcstr );
 rtn[size] = 0;
 return rtn;
 }

//将windows类型转换成jstring类型 

C代码   

 jstring WindowsTojstring( JNIEnv* env, char* str )
 {
 jstring rtn = 0;
 int slen = strlen(str);
 unsigned short * buffer = 0;
 if( slen == 0 )
 rtn = (env)->NewStringUTF(str );
 else
 {
 int length = MultiByteToWideChar( CP_ACP, 0, (LPCSTR)str, slen, NULL, 0 );
 buffer = (unsigned short *)malloc( length*2 + 1 );
 if( MultiByteToWideChar( CP_ACP, 0, (LPCSTR)str, slen, (LPWSTR)buffer, length ) >0 )
 rtn = (env)->NewString( (jchar*)buffer, length );
 }
 if( buffer )
 free( buffer );
 return rtn;
 }
 /*JNIEXPORT jstring JNICALL Java_test_cs_web_SWIFTAlianceCASmfTest_strcal
 (JNIEnv *env, jclass obj, jstring jstr1, jstring jstr2)
 {
 jbyteArray bytes = 0;
 jthrowable exc;
 char *pszResult = NULL;
 char *pszSTR1 = NULL;
 char *pszSTR2 = NULL;

 pszSTR1 = jstringTostring(env, jstr1);
 pszSTR2 = jstringTostring(env, jstr2);


 int nlen = sizeof(char)*(strlen(pszSTR1)+strlen(pszSTR2));
 pszResult = (char*)malloc(nlen);
 strcpy(pszResult, pszSTR1);
 strcat(pszResult, pszSTR2);

 jstring jstrRe = stoJstring(env, pszResult);
 free(pszSTR1);
 free(pszSTR2);
 free(pszResult);
 return(jstrRe);
 }
 */

jni object的使用 

每一个jni格式的dll中的object对应该java里面的一个类。 
如下例有一个 ObjData类，类中有成员bData ,Len 
public class ObjData { 
  public byte[]  bData; 
  public int Len;        
} 
//------------------------jni获得传过来的Object类型的变量objDataIn-------- 

jclass clazz =(env)->FindClass("ObjData"); 

//从传进来的对象中取出byte[] 

C代码   

 jfieldID byteData = (env)->GetFieldID(clazz,"bData","[B");
 jbyteArray pDataIn = (jbyteArray) (env)->GetObjectField(objDataIn, byteData);
 jsize theArrayLeng = env->GetArrayLength(pDataIn);

//byte[]转为BYTE[] 

C代码   

 jbyte * arrayBody = env->GetByteArrayElements(pDataIn,0);
 BYTE * jDataIn = (BYTE *)arrayBody;

//将BYTE数组转为jarray 

C代码   

 jbyte* byte = (jbyte*)jDataOut;
 jbyteArray jarray = env->NewByteArray(theArrayLeng);
 env->SetByteArrayRegion(jarray, 0, theArrayLeng, byte);

//给每一个实例的变量付值 

C代码   

 (env)->SetObjectField(objDataIn,byteData,jarray);
 (env)->SetIntField(objDataIn,pDataInLen,jDataInLen);
 (env)->ReleaseByteArrayElements(pDataIn, arrayBody, 0);

其他参考： 
Java 通过JNI调用C或者CPP代码 
http://blog.csdn.net/kenera/archive/2009/02/16/3895343.aspx
http://apps.hi.baidu.com/share/detail/15732549
http://dniit.blog.163.com/blog/static/28012894200842810332491/
http://hi.baidu.com/liangwind/blog/item/7dcce2c9729d1d1e7f3e6f49.html