List All the Classes Loaded in the Java Virtual Machine (JVM)

List All the Classes Loaded in the JVM

The Java Virtual Machine (JVM) is an incredible tool that can be used to run and execute Java programs. But what’s even more amazing is that the JVM can dynamically load and unload classes as needed. In this article, we’ll look at how to list all the classes that are currently loaded in the JVM.

Using Java Managements Extensions (JMX)

The easiest way to get a list of all the classes currently loaded in the JVM is to use the Java Management Extensions (JMX). JMX provides access to the RuntimeMXBean, which can be used to retrieve a list of all the classes that have been loaded into the JVM.

To use the RuntimeMXBean to get a list of all the classes loaded in the JVM, you’ll first need to create an MBeanServerConnection. Once you’ve done that, you can use the getLoadedClasses() method to return an array of all the classes currently loaded in the JVM:

MBeanServerConnection mbs = ... // create mbean server connection 
Class<?>[] classes = mbs.getClasses();
for (Class<?> cls : classes) {
    System.out.println(cls.getName());
}

Using Java Virtual Machine Tools Interface (JVMTI)

Another option for listing the classes currently loaded in the JVM is to use the Java Virtual Machine Tools Interface (JVMTI). JVMTI is a powerful tool that can be used to instrument and monitor the JVM. It can also be used to query the JVM for information about its state.

To get a list of all the classes currently loaded in the JVM using JVMTI, you’ll first need to use the GetLoadedClasses() function to retrieve an array of ClassID objects. Once you have the array of ClassID objects, you can then loop through the array and use the GetClassSignature() function to get the fully qualified name of each class:

jvmtiEnv *jvmti = ... // get jvmti environment 
jint classCount;
jclass *classes;
jvmti->GetLoadedClasses(&classCount, &classes);
for (int i = 0; i < classCount; i++) {
    char *sig;
    jvmti->GetClassSignature(classes[i], &sig, NULL);
    std::cout << sig << std::endl;
    jvmti->Deallocate((unsigned char *) sig);
}

Conclusion

In this article, we looked at two different ways to get a list of all the classes currently loaded in the JVM. We started by looking at how to use the Java Management Extensions (JMX) to retrieve a list of all the classes loaded in the JVM. We then explored how to use the Java Virtual Machine Tools Interface (JVMTI) to get a list of all the classes currently loaded in the JVM.

By using these two techniques, developers can get a good understanding of the state of their JVM and the classes that are currently loaded in it.