[BAEL-4533] get class names from a jar

core-java-modules/core-java-jar/.gitignore

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+!src/test/resources/example-jar/stripe-0.0.1-SNAPSHOT.jar

core-java-modules/core-java-jar/src/main/java/com/baeldung/jar/GetClassNamesFromJar.java

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+package com.baeldung.jar;
+
+import java.io.File;
+import java.io.IOException;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.util.Enumeration;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.jar.JarEntry;
+import java.util.jar.JarFile;
+
+public class GetClassNamesFromJar {
+
+    public static Set<String> getClassNamesFromJarFile(File givenFile) throws IOException {
+        Set<String> classNames = new HashSet<>();
+        try (JarFile jarFile = new JarFile(givenFile)) {
+            Enumeration<JarEntry> e = jarFile.entries();
+            while (e.hasMoreElements()) {
+                JarEntry jarEntry = e.nextElement();
+                if (jarEntry.getName().endsWith(".class")) {
+                    String className = jarEntry.getName()
+                      .replace("/", ".")
+                      .replace(".class", "");
+                    classNames.add(className);
+                }
+            }
+            return classNames;
+        }
+    }
+
+    public static Set<Class> getClassesFromJarFile(File jarFile) throws IOException, ClassNotFoundException {
+        Set<String> classNames = getClassNamesFromJarFile(jarFile);
+        Set<Class> classes = new HashSet<>(classNames.size());
+        try (URLClassLoader cl = URLClassLoader.newInstance(new URL[] { new URL("jar:file:" + jarFile + "!/") })) {
+            for (String name : classNames) {
+                Class clazz = cl.loadClass(name); // Loading the class by its name
+                classes.add(clazz);
+            }
+        }
+        return classes;
+    }
+}

core-java-modules/core-java-jar/src/test/java/com/baeldung/jar/GetClassNamesFromJarUnitTest.java

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+package com.baeldung.jar;
+
+import com.google.common.collect.Sets;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.io.File;
+import java.io.IOException;
+import java.net.URISyntaxException;
+import java.util.Arrays;
+import java.util.Objects;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+public class GetClassNamesFromJarUnitTest {
+    private static final String JAR_PATH = "example-jar/stripe-0.0.1-SNAPSHOT.jar";
+    private static final Set<String> EXPECTED_CLASS_NAMES = Sets.newHashSet(
+      "com.baeldung.stripe.StripeApplication",
+      "com.baeldung.stripe.ChargeRequest",
+      "com.baeldung.stripe.StripeService",
+      "com.baeldung.stripe.ChargeRequest$Currency",
+      "com.baeldung.stripe.ChargeController",
+      "com.baeldung.stripe.CheckoutController");
+
+    @Test
+    public void givenJarFilePath_whenLoadClassNames_thenGetClassNames() throws IOException, URISyntaxException {
+        File jarFile = new File(Objects.requireNonNull(getClass().getClassLoader().getResource(JAR_PATH)).toURI());
+        Set<String> classNames = GetClassNamesFromJar.getClassNamesFromJarFile(jarFile);
+        Assert.assertEquals(EXPECTED_CLASS_NAMES, classNames);
+    }
+
+    @Test
+    public void givenJarFilePath_whenLoadClass_thenGetClassObjects() throws IOException, ClassNotFoundException, URISyntaxException {
+        File jarFile = new File(Objects.requireNonNull(getClass().getClassLoader().getResource(JAR_PATH)).toURI());
+        Set<Class> classes = GetClassNamesFromJar.getClassesFromJarFile(jarFile);
+        Set<String> names = classes.stream().map(Class::getName).collect(Collectors.toSet());
+        Assert.assertEquals(EXPECTED_CLASS_NAMES, names);
+    }
+}