JNI的某些数组和字符串类型转换

 JNICC++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

http://blog.csdn.net/buleriver/article/details/6898007

原文：http://blog.csdn.net/xuxinyl/article/details/6718780