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BAEL-4302 : How can I list all classes loaded in a specific class loader
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‎core-java-modules/core-java-jvm-2/src/main/java/com/baeldung/loadedclasslisting/ClassLoaderType.java‎

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package com.baeldung.loadedclasslisting;
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public enum ClassLoaderType {
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SYSTEM, EXTENSION, BOOTSTRAP, CUSTOM
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}

‎core-java-modules/core-java-jvm-2/src/main/java/com/baeldung/loadedclasslisting/Launcher.java‎

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package com.baeldung.loadedclasslisting;
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import java.lang.reflect.Method;
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import java.util.Arrays;
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import com.baeldung.loadedclasslisting.customLoader.ClassLoaderInfo;
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import com.baeldung.loadedclasslisting.customLoader.CustomClassLoader;
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public class Launcher {
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private static ClassLoader customClassLoader;
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public static void main(String[] args) {
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printClassesLoadedBy(ClassLoaderType.BOOTSTRAP);
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printClassesLoadedBy(ClassLoaderType.SYSTEM);
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printClassesLoadedBy(ClassLoaderType.EXTENSION);
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printClassesLoadedBy(ClassLoaderType.CUSTOM);
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}
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private static void printClassesLoadedBy(ClassLoaderType classLoaderType) {
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Class<?>[] classes;
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if (classLoaderType.equals(ClassLoaderType.CUSTOM)) {
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customClassLoader = customClassLoading();
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classes = ListLoadedClassesAgent.listLoadedClasses(customClassLoader);
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} else {
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classes = ListLoadedClassesAgent.listLoadedClasses(classLoaderType);
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}
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Arrays.asList(classes)
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.forEach(clazz -> System.out.println(
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classLoaderType + " ClassLoader : " + clazz.getCanonicalName()));
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}
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private static CustomClassLoader customClassLoading() {
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CustomClassLoader customClassLoader = new CustomClassLoader();
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Class<?> c;
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try {
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c = customClassLoader.findClass(ClassLoaderInfo.class.getName());
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Object ob = c.getDeclaredConstructor()
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.newInstance();
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Method md = c.getMethod("printClassLoaders");
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md.invoke(ob);
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} catch (Exception e) {
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e.printStackTrace();
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}
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return customClassLoader;
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}
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}

‎core-java-modules/core-java-jvm-2/src/main/java/com/baeldung/loadedclasslisting/ListLoadedClassesAgent.java‎

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package com.baeldung.loadedclasslisting;
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import java.lang.instrument.Instrumentation;
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public class ListLoadedClassesAgent {
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private static Instrumentation instrumentation;
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public static void premain(String agentArgs, Instrumentation instrumentation) {
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ListLoadedClassesAgent.instrumentation = instrumentation;
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}
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public static Class<?>[] listLoadedClasses(ClassLoaderType classLoaderType) {
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if (instrumentation == null) {
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throw new IllegalStateException(
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"ListLoadedClassesAgent is not initialized.");
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}
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return instrumentation.getInitiatedClasses(
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getClassLoader(classLoaderType));
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}
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public static Class<?>[] listLoadedClasses(ClassLoader classLoader) {
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if (instrumentation == null) {
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throw new IllegalStateException(
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"ListLoadedClassesAgent is not initialized.");
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}
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return instrumentation.getInitiatedClasses(classLoader);
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}
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private static ClassLoader getClassLoader(ClassLoaderType classLoaderType) {
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ClassLoader classLoader = null;
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switch (classLoaderType) {
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case SYSTEM:
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classLoader = ClassLoader.getSystemClassLoader();
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break;
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case EXTENSION:
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classLoader = ClassLoader.getSystemClassLoader().getParent();
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break;
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case BOOTSTRAP:
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break;
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default:
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break;
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}
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return classLoader;
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}
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}

‎core-java-modules/core-java-jvm-2/src/main/java/com/baeldung/loadedclasslisting/MANIFEST.MF‎

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Premain-Class: com.baeldung.loadedclasslisting.ListLoadedClassesAgent

‎core-java-modules/core-java-jvm-2/src/main/java/com/baeldung/loadedclasslisting/customLoader/ClassLoaderInfo.java‎

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package com.baeldung.loadedclasslisting.customLoader;
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import java.util.ArrayList;
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public class ClassLoaderInfo {
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public void printClassLoaders() throws ClassNotFoundException {
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System.out.println("Classloader of this class:" + ClassLoaderInfo.class.getClassLoader());
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System.out.println("Classloader of ArrayList:" + ArrayList.class.getClassLoader());
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}
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}

‎core-java-modules/core-java-jvm-2/src/main/java/com/baeldung/loadedclasslisting/customLoader/CustomClassLoader.java‎

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package com.baeldung.loadedclasslisting.customLoader;
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import java.io.ByteArrayOutputStream;
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import java.io.File;
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import java.io.IOException;
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import java.io.InputStream;
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public class CustomClassLoader extends ClassLoader {
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@Override
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public Class<?> findClass(String name) throws ClassNotFoundException {
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byte[] b = loadClassFromFile(name);
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return defineClass(name, b, 0, b.length);
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}
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private byte[] loadClassFromFile(String fileName) {
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InputStream inputStream = getClass().getClassLoader()
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.getResourceAsStream(fileName.replace('.', File.separatorChar) + ".class");
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byte[] buffer;
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ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
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int nextValue = 0;
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try {
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while ((nextValue = inputStream.read()) != -1) {
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byteStream.write(nextValue);
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}
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} catch (IOException e) {
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e.printStackTrace();
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}
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buffer = byteStream.toByteArray();
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return buffer;
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}
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}

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