JNI trouble
Hi,
Below is my attempt at calling a C++ function (DllLoader.processQuery), which in turn calls a Java function (getParameter) of the calling class. The execution reaches the C++ function, the trouble is that the jmethodID I get is NULL. Can you tell me where I went wrong?
Thanks for your help,
Miguel
// java code
publicclass RouteServletextends HttpServlet{
publicvoid doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException{
String respStr = DllLoader.processQuery();
}
public String getParameter(String name){
return request.getParameter(name);
}
}
class DllLoader{
publicstaticnative String processQuery();
}
// C++ code
JNIEXPORT jstring JNICALL Java_DllLoader_processQuery
(JNIEnv *env, jclass cl){
jmethodID id_getParameter = env->GetMethodID(cl,"getParameter","(Ljava/lang/String;)Ljava/lang/String;");
[1748 byte] By [
MCorazao3a] at [2007-11-26 20:17:48]
Miguel,
in your call:
env->GetMethodID(cl,"getParameter","(Ljava/lang/String
;)Ljava/lang/String;");
cl referes to class DllLoader and not RouteServlet. getParameter is not a method of DllLoader but of RouteServlet.
to get the right class you need to call:
jclass right_cl= env->FindClass("RouteServlet ");
Daniel
Message was edited by:
Daniel.Barkan
Message was edited by:
Daniel.Barkan
Daniel,
Thank you so much for your help. It definitely put me on the right track. However I'm not at the end of the trip yet. You will notice below that I try to call the Java method using the objct id I got with your help. The trouble is that I get a null value for jvalueObj. If you are kind enough to let me know what is wrong this time, perhaps you can take a look at the rest of the code where I attempt to cast the object I will hopefully get to a jstring, and then get the character string.
Thanks again,
Miguel
public class RouteServlet extends HttpServlet {
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String respStr = DllLoader.processQuery(this);
}
public String getParameter(String name) {
return request.getParameter(name);
}
}
class DllLoader {
public static native String processQuery(RouteServlet obj);
}
JNIEXPORT jstring JNICALL Java_DllLoader_processQuery
(JNIEnv *env, jclass cl, jobject rtServ) {
jclass rtServ_cl= env->FindClass("RouteServlet");
jmethodID id_getParameter = env->GetMethodID(rtServ_cl,"getParameter","(Ljava/lang/String;)Ljava/lang/String;");
jstring jstrParam = env->NewStringUTF("cmd");
jobject jvalueObj = env->CallObjectMethod(rtServ,id_getParameter,jstrParam);
jstring jvalueStr = (jstring)jvalueObj;
jsize lengthStr = env->GetStringUTFLength(jvalueStr);
const jbyte *bytesStr = (const signed char *)env->GetStringUTFChars(jvalueStr,JNI_FALSE);
> Daniel,
> Thank you so much for your help. It definitely put me
> on the right track. However I'm not at the end of the
> trip yet. You will notice below that I try to call
> the Java method using the objct id I got with your
> help. The trouble is that I get a null value for
> jvalueObj.
You should be checking the return values of all your JNI calls looking for errors/exceptions.
