JNI trouble

Question

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
public class RouteServlet extends HttpServlet {
  public void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
    String respStr = DllLoader.processQuery();
  public String getParameter(String name) {
    return request.getParameter(name);
class DllLoader {
  public static native 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;");

Answer 1

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);