adding log4j2.forceTCLOnly option

Author: rmannibucau

log4j-api/src/main/java/org/apache/logging/log4j/util/LoaderUtil.java

@@ -44,6 +44,7 @@ public final class LoaderUtil {
      * @since 2.1
      */
     public static final String IGNORE_TCCL_PROPERTY = "log4j.ignoreTCL";
+    public static final String FORCE_TCL_ONLY_PROPERTY = "log4j.forceTCLOnly";
 
     private static final SecurityManager SECURITY_MANAGER = System.getSecurityManager();
 
@@ -53,6 +54,8 @@ public final class LoaderUtil {
 
     private static final boolean GET_CLASS_LOADER_DISABLED;
 
+    protected static Boolean forceTcclOnly;
+
     private static final PrivilegedAction<ClassLoader> TCCL_GETTER = new ThreadContextClassLoaderGetter();
 
     static {
@@ -109,21 +112,23 @@ public static ClassLoader[] getClassLoaders() {
         List<ClassLoader> classLoaders = new ArrayList<>();
         ClassLoader tcl = getThreadContextClassLoader();
         classLoaders.add(tcl);
-        ClassLoader current = LoaderUtil.class.getClassLoader();
-        if (current != tcl) {
-            classLoaders.add(current);
-            ClassLoader parent = current.getParent();
+        if (!isForceTccl()) {
+            ClassLoader current = LoaderUtil.class.getClassLoader();
+            if (current != tcl) {
+                classLoaders.add(current);
+                ClassLoader parent = current.getParent();
+                while (parent != null && !classLoaders.contains(parent)) {
+                    classLoaders.add(parent);
+                }
+            }
+            ClassLoader parent = tcl.getParent();
             while (parent != null && !classLoaders.contains(parent)) {
                 classLoaders.add(parent);
+                parent = parent.getParent();
+            }
+            if (!classLoaders.contains(ClassLoader.getSystemClassLoader())) {
+                classLoaders.add(ClassLoader.getSystemClassLoader());
             }
-        }
-        ClassLoader parent = tcl.getParent();
-        while (parent != null && !classLoaders.contains(parent)) {
-            classLoaders.add(parent);
-            parent = parent.getParent();
-        }
-        if (!classLoaders.contains(ClassLoader.getSystemClassLoader())) {
-            classLoaders.add(ClassLoader.getSystemClassLoader());
         }
         return classLoaders.toArray(new ClassLoader[classLoaders.size()]);
     }
@@ -260,6 +265,21 @@ private static boolean isIgnoreTccl() {
         return ignoreTCCL;
     }
 
+    private static boolean isForceTccl() {
+        if (forceTcclOnly == null) {
+            // PropertiesUtil.getProperties() uses that code path so don't use that!
+            forceTcclOnly = System.getSecurityManager() == null ?
+                    Boolean.getBoolean(FORCE_TCL_ONLY_PROPERTY) :
+                    AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
+                        @Override
+                        public Boolean run() {
+                            return Boolean.getBoolean(FORCE_TCL_ONLY_PROPERTY);
+                        }
+                    });
+        }
+        return forceTcclOnly;
+    }
+
     /**
      * Finds classpath {@linkplain URL resources}.
      *
@@ -279,9 +299,9 @@ public static Collection<URL> findResources(final String resource) {
     static Collection<UrlResource> findUrlResources(final String resource) {
         // @formatter:off
         final ClassLoader[] candidates = {
-                getThreadContextClassLoader(), 
-                LoaderUtil.class.getClassLoader(),
-                GET_CLASS_LOADER_DISABLED ? null : ClassLoader.getSystemClassLoader()};
+                getThreadContextClassLoader(),
+                isForceTccl() ? null : LoaderUtil.class.getClassLoader(),
+                isForceTccl() || GET_CLASS_LOADER_DISABLED ? null : ClassLoader.getSystemClassLoader()};
         // @formatter:on
         final Collection<UrlResource> resources = new LinkedHashSet<>();
         for (final ClassLoader cl : candidates) {

log4j-api/src/test/java/org/apache/logging/log4j/util/LoaderUtilTest.java

@@ -0,0 +1,58 @@
+/*
+ * 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.logging.log4j.util;
+
+import static org.junit.Assert.assertEquals;
+
+import java.net.URL;
+import java.util.Collections;
+import java.util.Enumeration;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+public class LoaderUtilTest {
+    @Before
+    @After
+    public void reset() {
+        LoaderUtil.forceTcclOnly = null;
+    }
+
+    @Test
+    public void systemClassLoader() {
+        final Thread thread = Thread.currentThread();
+        final ClassLoader tccl = thread.getContextClassLoader();
+
+        LoaderUtil.forceTcclOnly = true;
+        final ClassLoader loader = new ClassLoader(tccl) {
+            @Override
+            public Enumeration<URL> getResources(final String name) {
+                return Collections.emptyEnumeration();
+            }
+        };
+        thread.setContextClassLoader(loader);
+        try {
+            assertEquals(0, LoaderUtil.findUrlResources("Log4j-charsets.properties").size());
+
+            LoaderUtil.forceTcclOnly = false;
+            assertEquals(1, LoaderUtil.findUrlResources("Log4j-charsets.properties").size());
+        } finally {
+            thread.setContextClassLoader(tccl);
+        }
+    }
+}