这两天一直在研究jstring 和char* 之间是如何转换的。现把自己成功运行例子贴出来。

//jstring to char*
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); 软件开发网 www.mscto.com
                 memcpy(rtn, ba, alen);
                 rtn[alen] = 0;
       }
       env->ReleaseByteArrayElements(barr, ba, 0);
       return rtn;
}

//char* to jstring
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 b

ytes = 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);
}

//invoke function
JNIEXPORT jstring JNICALL Java_test_cs_web_SWIFTAl

ianceCASmfTest_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);
}

Note: 函数中间有一些签名的定义，不是很好理解。细节请参考sun的jni文档介绍or command javap