Can not locate Java class using JNI within C++ DLL

Question

I am using trying to use JNI to call a Java class from C++. The Java class uses JMS to send messages to a JMS message queue. At first I coded the C++ in a console application that created the JavaVM and used JNI to access the Java class. All worked fine. Then I called the Java class using JNI from threads and ran into the problem of the Java class not able to locate the JMS related classes. This was solved by placing the following line in the constructor of the Java class.
Thread.currentThread().setContextClassLoader(ClassLoader.getSystemClassLoader());
Then I moved the JNI code from a console application to a DLL in specific an extension DLL that is called by SQL Server or Oracle server. The DLL will use JNI to call the Java class and send messages to a JMS message queue.
The problem I am having now when the DLL code is called by SQL Server the call to
JNI_CreateJavaVM
appears to work correctly but the call to find the Java class using
jvmEnv->FindClass(pName)
fails. It appears the is a class loading problem which occurs due to the fact JNI is called from a DLL. When the VM is created I pass the class path information using the statement
-Djava.class.path=
And as I stated before it all works when running from a console application. I am new to JNI and really need help in the form of some sample code that will solve this problem. I believe I need to somehow load the classpath information from the DLL but I can not find examples on how to do this using JNI. I have tried several ways using URLClassLoader and getSystemClassLoader from JNI and either it does not work or it crashes very badly.
I used the following code to determine what the existing class path is and the string returns empty.
jcls = jvmEnv->FindClass("java/lang/System");
jmid = jvmEnv->GetStaticMethodID(jcls, "getProperty", "(Ljava/lang/String;)Ljava/lang/String;");
jstrClassPath = jvmEnv->NewStringUTF("java.class.path");
jstr = (jstring)jvmEnv->CallStaticObjectMethod(jcls, jmid, jstrClassPath);
m_jstr = (jstring)jvmEnv->NewGlobalRef(jstr);
pstr = jvmEnv->GetStringUTFChars(m_jstr, 0);
Can anyone please help with example code that will solve this problem. Thanks in advance for any help.
Charles�

Answer 1

I have determined the problem occurs when the application/component is compiled using VC 6.0. The test application was compiled using VC 7.1 and works correctly by locating the class path information. If the test application is compiled using VC 6.0 it has the same problem.
The jvm.dll I am using is version 1.4.2.80. Currently this is not an option to compile all the applications that use JNI using VC 7.1 so can someone please tell me how to solve this problem.