Use Brotli4jLoader.isAvailable() instead of relying on class presence.

httpclient5/src/main/java/org/apache/hc/client5/http/impl/Brotli4jRuntime.java

@@ -35,20 +35,36 @@
 @Contract(threading = ThreadingBehavior.STATELESS)
 public final class Brotli4jRuntime {
 
-    private static final String BROTLI = "com.aayushatharva.brotli4j.Brotli4jLoader";
+    private static final String BROTLI4J_LOADER = "com.aayushatharva.brotli4j.Brotli4jLoader";
+
+    private static final String IS_AVAILABLE = "isAvailable";
 
     private Brotli4jRuntime() {
     }
 
     /**
-     * @return {@code true} if {@code com.aayushatharva.brotli4j} can be loaded
-     * by the current class loader; {@code false} otherwise
+     * @return {@code true} if Brotli4j and its native library are available
+     * to the HttpClient class loader; {@code false} otherwise
      */
     public static boolean available() {
+        return available(Brotli4jRuntime.class.getClassLoader());
+    }
+
+    /**
+     * Determines whether Brotli4j and its native library are available to the
+     * given class loader.
+     *
+     * @param classLoader the class loader used to locate Brotli4j
+     * @return {@code true} if Brotli4j reports that its native runtime is
+     * available; {@code false} otherwise
+     */
+    static boolean available(final ClassLoader classLoader) {
         try {
-            Class.forName(BROTLI, false, Brotli4jRuntime.class.getClassLoader());
-            return true;
-        } catch (ClassNotFoundException | LinkageError ex) {
+            final Class<?> loaderClass =
+                    Class.forName(BROTLI4J_LOADER, true, classLoader);
+            return Boolean.TRUE.equals(
+                    loaderClass.getMethod(IS_AVAILABLE).invoke(null));
+        } catch (final ReflectiveOperationException | LinkageError ex) {
             return false;
         }
     }

httpclient5/src/test/java/org/apache/hc/client5/http/impl/Brotli4jRuntimeTest.java

@@ -0,0 +1,84 @@
+/*
+ * ====================================================================
+ * 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.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation.  For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ *
+ */
+package org.apache.hc.client5.http.impl;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+import java.io.File;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.util.UUID;
+
+import com.aayushatharva.brotli4j.Brotli4jLoader;
+import com.aayushatharva.brotli4j.service.BrotliNativeProvider;
+import org.junit.jupiter.api.Test;
+
+class Brotli4jRuntimeTest {
+
+    private static final String LIBRARY_PATH_PROPERTY =
+            "brotli4j.library.path";
+
+    @Test
+    void unavailableWhenNativeLibraryCannotBeLoaded() throws Exception {
+        final URL brotli4jLocation = Brotli4jLoader.class
+                .getProtectionDomain()
+                .getCodeSource()
+                .getLocation();
+        final URL serviceLocation = BrotliNativeProvider.class
+                .getProtectionDomain()
+                .getCodeSource()
+                .getLocation();
+
+        final File missingLibrary = new File(
+                "target",
+                "missing-brotli-" + UUID.randomUUID());
+        final String previousLibraryPath = System.setProperty(
+                LIBRARY_PATH_PROPERTY,
+                missingLibrary.getAbsolutePath());
+
+        try (URLClassLoader classLoader = new URLClassLoader(
+                new URL[] {brotli4jLocation, serviceLocation},
+                null)) {
+
+            assertNotNull(Class.forName(
+                    "com.aayushatharva.brotli4j.Brotli4jLoader",
+                    false,
+                    classLoader));
+
+            assertFalse(Brotli4jRuntime.available(classLoader));
+        } finally {
+            if (previousLibraryPath != null) {
+                System.setProperty(
+                        LIBRARY_PATH_PROPERTY,
+                        previousLibraryPath);
+            } else {
+                System.clearProperty(LIBRARY_PATH_PROPERTY);
+            }
+        }
+    }
+}