JNI 的某些数组和字符串类型转换

jbytearray转c++byte数组

C代码

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

jbyteArray 转 c++中的BYTE[]

C代码

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

C代码

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 *

C代码

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

char* 转jstring

C代码

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*

C代码

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

C代码

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.     }  
11.     env->SetByteArrayRegion(firstMacArray, 0, 6, bytes );  
12. return firstMacArray;  
13. } 

//jstring to char*

C代码

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

C代码

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

C代码

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

C代码

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;
28. pszSTR1 = jstringTostring(env, jstr1);
29. pszSTR2 = jstringTostring(env, jstr2);
32. int nlen = sizeof(char)*(strlen(pszSTR1)+strlen(pszSTR2));
33. pszResult = (char*)malloc(nlen);
34. strcpy(pszResult, pszSTR1);
35. strcat(pszResult, pszSTR2);
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[]

C代码

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[]

C代码

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

//将BYTE数组转为jarray

C代码

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

C代码

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