FindClass() Problem Pls Help.. (URGENT!!)

Question

Hi,
I trying to use the files from the book "JNI Programmer's Guide & Specifications" - Ch. 7., to create JVM & call a java method from c routine.
I m working on Solaris machine. JVM is 1.1, so the correct part of the version independent code runs (refer to invoke.c below)
LD_LIBRARY_PATH is set correctly. invoke.c is complied correctly with no errors. All the files namely Prog.java, Prog.class, invoke.c, a.out are in the same directoy "/home/top/atm".
When executable file is run. JVM is created. But FindClass() returns with NULL value. !!!
When I try to run Prog.java from the commandline using "java Prog Hello" it runs good.
It just simply won't find the Prog.class in it's current directory. ???
If instead, "java/util/Date" is passed to FindClass(), it finds it.
The classpath in the program is also modified & there is no typo error or case-sensitivity related errors.
I m also printing classpath passed to JVM in the program. It has my included path "/home/top/atm", along with other system classpath(s).
I m banging my head over this problem, since 2 days. Hence I tried to use reference implementation files. It still will not work..
Can anyone pls be patient & help me. I'll really appreciate this.
Thanks a lot,
Following is the code of 2 files..
Prog.java
public class Prog
public static void main(String[] args)
System.out.println("Hello World" + args[0]);
& invoke.c
#include <jni.h>
#define PATH_SEPARATOR ':' /* define it to be ':' on Solaris */
#define USER_CLASSPATH "/home/top/atm" /* where Prog.class is */
main() {
JNIEnv *env;
JavaVM *jvm;
jint res;
jclass cls;
jmethodID mid;
jstring jstr;
jclass stringClass;
jobjectArray args;
#ifdef JNI_VERSION_1_2
JavaVMInitArgs vm_args;
JavaVMOption options[1];
options[0].optionString =
"-Djava.class.path=" USER_CLASSPATH;
vm_args.version = 0x00010002;
vm_args.options = options;
vm_args.nOptions = 1;
vm_args.ignoreUnrecognized = JNI_TRUE;
/* Create the Java VM */
res = JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args);
#else
JDK1_1InitArgs vm_args;
char classpath[102400];
vm_args.version = 0x00010001;
JNI_GetDefaultJavaVMInitArgs(&vm_args);
/* Append USER_CLASSPATH to the default system class path */
sprintf(classpath, "%s%c%s",
vm_args.classpath, PATH_SEPARATOR, USER_CLASSPATH);
vm_args.classpath = classpath;
/* Create the Java VM */
res = JNI_CreateJavaVM(&jvm, &env, &vm_args);
fprintf(stderr, "JVM Created !!! with # %d\n", res);
#endif /* JNI_VERSION_1_2 */
if (res < 0) {
fprintf(stderr, "Can't create Java VM\n");
exit(1);
fprintf(stderr, "ClassPath is : %s\n", classpath);
cls = (*env)->FindClass(env, "Prog");
if (cls == NULL) {
goto destroy;
     fprintf(stderr, "Class Found !!\n");
mid = (*env)->GetStaticMethodID(env, cls, "main",
"([Ljava/lang/String;)V");
if (mid == NULL) {
goto destroy;
jstr = (*env)->NewStringUTF(env, " from C!");
if (jstr == NULL) {
goto destroy;
stringClass = (*env)->FindClass(env, "java/lang/String");
args = (*env)->NewObjectArray(env, 1, stringClass, jstr);
if (args == NULL) {
goto destroy;
(*env)->CallStaticVoidMethod(env, cls, mid, args);
destroy:
if ((*env)->ExceptionOccurred(env)) {
(*env)->ExceptionDescribe(env);
(*jvm)->DestroyJavaVM(jvm);
----------------------------------------

Answer 1

Hi , I got the exact same problem as you did. Can you
please let me know if you solve this issue already ?When FindClass returns null it means it threw an exception. The first step is to get that exception and print it out.
The error is probably class not found. And just as with java only that means your class path is not correct.