[LANG-1487] Add ClassLoaderUtils with toString() implementations. (#453)

[LANG-1487] Add ClassLoaderUtils with toString() implementations for
URLClassLoader.

src/main/java/org/apache/commons/lang3/ClassLoaderUtils.java

@@ -0,0 +1,53 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.lang3;
+
+import java.net.URLClassLoader;
+import java.util.Arrays;
+
+/**
+ * Helps work with {@link ClassLoader}.
+ *
+ * @since 3.10
+ */
+public class ClassLoaderUtils {
+
+    /**
+     * Converts the given class loader to a String calling {@link #toString(URLClassLoader)}.
+     *
+     * @param classLoader to URLClassLoader to convert.
+     * @return the formated string.
+     */
+    public static String toString(final ClassLoader classLoader) {
+        if (classLoader instanceof URLClassLoader) {
+            return toString((URLClassLoader) classLoader);
+        }
+        return classLoader.toString();
+    }
+
+    /**
+     * Converts the given URLClassLoader to a String in the format
+     * {@code "URLClassLoader.toString() + [URL1, URL2, ...]"}.
+     *
+     * @param classLoader to URLClassLoader to convert.
+     * @return the formated string.
+     */
+    public static String toString(final URLClassLoader classLoader) {
+        return classLoader + Arrays.toString(classLoader.getURLs());
+    }
+}

src/test/java/org/apache/commons/lang3/ClassLoaderUtilsTest.java

@@ -0,0 +1,50 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.lang3;
+
+import java.io.IOException;
+import java.net.URL;
+import java.net.URLClassLoader;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests {@link ClassLoaderUtils}.
+ */
+public class ClassLoaderUtilsTest {
+
+    @Test
+    public void testToString_ClassLoader() throws IOException {
+        final URL url = new URL("http://localhost");
+        try (URLClassLoader urlClassLoader = new URLClassLoader(new URL[] { url })) {
+            @SuppressWarnings("resource")
+            final ClassLoader classLoader = urlClassLoader;
+            Assertions.assertEquals(String.format("%s[%s]", classLoader, url), ClassLoaderUtils.toString(classLoader));
+        }
+    }
+
+    @Test
+    public void testToString_URLClassLoader() throws IOException {
+        final URL url = new URL("http://localhost");
+        try (URLClassLoader urlClassLoader = new URLClassLoader(new URL[] { url })) {
+            Assertions.assertEquals(String.format("%s[%s]", urlClassLoader, url),
+                    ClassLoaderUtils.toString(urlClassLoader));
+        }
+    }
+}