某些数组和字符串类型转换（转）

jbytearray转c++byte数组

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

jbyteArray 转 c++中的BYTE[]

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

C++中的BYTE[]转jbyteArray

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

jbyteArray 转 char *

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

char* 转jstring

1.  1 jstring WindowsTojstring(JNIEnv* env, char* str_tmp)
    2 {
    3  jstring rtn=0;
    4  int slen = (int)strlen(str_tmp);
    5  unsigned short* buffer=0;
    6  if(slen == 0)
    7  {
    8   rtn = env->NewStringUTF(str_tmp);
    9  }
   10  else
   11  {
   12   int length = MultiByteToWideChar(CP_ACP, 0, (LPCSTR)str_tmp, slen, NULL, 0);
   13   buffer = (unsigned short*)malloc(length*2+1);
   14   if(MultiByteToWideChar(CP_ACP, 0, (LPCSTR)str_tmp, slen, (LPWSTR)buffer, length) > 0)
   15   {
   16    rtn = env->NewString((jchar*)buffer, length);
   17   }
   18  }
   19  if(buffer)
   20  {
   21   free(buffer);
   22  }
   23  return rtn;
   24 }  

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*

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

JNI 返回 jbyteArray

 1 JNIEXPORT jbyteArray JNICALL Java_Test_getByteArray(JNIEnv *env, jobject obj)
 2 {
 3     jbyteArray firstMacArray = env->NewByteArray( 6 );
 4     ......
 5     jbyte *bytes = env->GetByteArrayElements( firstMacArray, 0);
 6     for ( int i = 0; i < sizeof( pAdapterInfo->Address ); i++ )
 7     {
 8        bytes[ i ] = pAdapterInfo->Address[ i ];
 9     }
10
11     env->SetByteArrayRegion(firstMacArray, 0, 6, bytes );
12     return firstMacArray;
13 }  

//jstring to char*

 1 char* jstringTostring(JNIEnv* env, jstring jstr)
 2 {
 3   char* rtn = NULL;
 4   jclass clsstring = env->FindClass("java/lang/String");
 5   jstring strencode = env->NewStringUTF("utf-8");
 6   jmethodID mid = env->GetMethodID(clsstring, "getBytes", "(Ljava/lang/String;)[B");
 7   jbyteArray barr= (jbyteArray)env->CallObjectMethod(jstr, mid, strencode);
 8   jsize alen = env->GetArrayLength(barr);
 9   jbyte* ba = env->GetByteArrayElements(barr, JNI_FALSE);
10   if (alen > 0)
11   {
12     rtn = (char*)malloc(alen + 1);
13     memcpy(rtn, ba, alen);
14     rtn[alen] = 0;
15   }
16   env->ReleaseByteArrayElements(barr, ba, 0);
17   return rtn;
18 }  

//char* to jstring

1 jstring stoJstring(JNIEnv* env, const char* pat)
2 {
3 jclass strClass = env->FindClass("Ljava/lang/String;");
4 jmethodID ctorID = env->GetMethodID(strClass, "<init>", "([BLjava/lang/String;)V");
5 jbyteArray bytes = env->NewByteArray(strlen(pat));
6 env->SetByteArrayRegion(bytes, 0, strlen(pat), (jbyte*)pat);
7 jstring encoding = env->NewStringUTF("utf-8");
8 return (jstring)env->NewObject(strClass, ctorID, bytes, encoding);
9 }   

//将jstring类型转换成windows类型

 1 char* jstringToWindows( JNIEnv *env, jstring jstr )
 2 {
 3 int length = (env)->GetStringLength(jstr );
 4 const jchar* jcstr = (env)->GetStringChars(jstr, 0 );
 5 char* rtn = (char*)malloc( length*2+1 );
 6 int size = 0;
 7 size = WideCharToMultiByte( CP_ACP, 0, (LPCWSTR)jcstr, length, rtn,(length*2+1), NULL, NULL );
 8 if( size <= 0 )
 9 return NULL;
10 (env)->ReleaseStringChars(jstr, jcstr );
11 rtn[size] = 0;
12 return rtn;
13 }  

//将windows类型转换成jstring类型

 1 jstring WindowsTojstring( JNIEnv* env, char* str )
 2 {
 3 jstring rtn = 0;
 4 int slen = strlen(str);
 5 unsigned short * buffer = 0;
 6 if( slen == 0 )
 7 rtn = (env)->NewStringUTF(str );
 8 else
 9 {
10 int length = MultiByteToWideChar( CP_ACP, 0, (LPCSTR)str, slen, NULL, 0 );
11 buffer = (unsigned short *)malloc( length*2 + 1 );
12 if( MultiByteToWideChar( CP_ACP, 0, (LPCSTR)str, slen, (LPWSTR)buffer, length ) >0 )
13 rtn = (env)->NewString( (jchar*)buffer, length );
14 }
15 if( buffer )
16 free( buffer );
17 return rtn;
18 }
19 /*JNIEXPORT jstring JNICALL Java_test_cs_web_SWIFTAlianceCASmfTest_strcal
20 (JNIEnv *env, jclass obj, jstring jstr1, jstring jstr2)
21 {
22 jbyteArray bytes = 0;
23 jthrowable exc;
24 char *pszResult = NULL;
25 char *pszSTR1 = NULL;
26 char *pszSTR2 = NULL;
27
28 pszSTR1 = jstringTostring(env, jstr1);
29 pszSTR2 = jstringTostring(env, jstr2);
30
31
32 int nlen = sizeof(char)*(strlen(pszSTR1)+strlen(pszSTR2));
33 pszResult = (char*)malloc(nlen);
34 strcpy(pszResult, pszSTR1);
35 strcat(pszResult, pszSTR2);
36
37 jstring jstrRe = stoJstring(env, pszResult);
38 free(pszSTR1);
39 free(pszSTR2);
40 free(pszResult);
41 return(jstrRe);
42 }
43 */  

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[]

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

//byte[]转为BYTE[]

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

//将BYTE数组转为jarray

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

//给每一个实例的变量付值

1 (env)->SetObjectField(objDataIn,byteData,jarray);
2 (env)->SetIntField(objDataIn,pDataInLen,jDataInLen);
3 (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

原文地址：https://www.cnblogs.com/zl1991/p/9188736.html