JNI: Calling Java Method with String as Parameter from C

16 Apr 2007 07:51:29 -0700

In my C Method i try to call a Method, which expects a String as
Parameter. Therefore the String will be created in the c function and
then passed to the java method. Everything works fine, expect of the
fact, that i get in the Java Method a String object with length 0 :(

The strange thing is, that in the c code the jstring object seems to
be correct (getUtfSize() returns the right length). But on Java Side
the length is 0. So what am i doing wrong???? I thought about it the
whole day without finding any solution!

Thanks for your help in advance!!!

Source Code:


    private synchronized boolean internalNotifyCallback(String obj)
        if(obj != null) {
            System.out.println("object is not null : " + obj);

            System.out.println("CloseNotify is " + closeNotify);
        return !closeNotify;

void listenXYZ(RXPARAMS par)

        jsize count;
    jmethodID jmid;
    jclass icls;
    jboolean continueListening = 1;

    char string[50];

    RXPARAMS prxParams = par;

    JNIEnv *env = par.env;


     icls = (*env)->GetObjectClass(env, prxParams.jobj);
    //get CallBack Address
     jmid = (*env)->GetMethodID(env, icls,

    writeLog("after getMID\n");
    if (jmid == 0){
        writeLog("jmid == NULL\n");

      const char *pWelt = "Hello World";

       jstring jStr = NULL;
    jStr = (*env)->NewStringUTF(env, pWelt);

    if (jStr != NULL){
        jsize size = (*env)->GetStringUTFLength(env,jStr);
        writeLog("Is Not Null. Size: %d \n", size);
        writeLog("Is Null\n");

     continueListening = (*env)->CallBooleanMethod(env, prxParams.jobj,
jmid, eventObj, jStr);

P.S. I know that my english isn't very good - but i try to improve it,
so please be lenient toward me ;)

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