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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements. See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache license, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License. You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the license for the specific language governing permissions and
15   * limitations under the license.
16   */
17  package org.apache.logging.log4j.util;
18  
19  import java.io.IOException;
20  import java.lang.reflect.InvocationTargetException;
21  import java.net.URL;
22  import java.security.AccessController;
23  import java.security.PrivilegedAction;
24  import java.util.ArrayList;
25  import java.util.Collection;
26  import java.util.Enumeration;
27  import java.util.LinkedHashSet;
28  import java.util.List;
29  import java.util.Objects;
30  
31  /**
32   * <em>Consider this class private.</em> Utility class for ClassLoaders.
33   *
34   * @see ClassLoader
35   * @see RuntimePermission
36   * @see Thread#getContextClassLoader()
37   * @see ClassLoader#getSystemClassLoader()
38   */
39  public final class LoaderUtil {
40  
41      /**
42       * System property to set to ignore the thread context ClassLoader.
43       *
44       * @since 2.1
45       */
46      public static final String IGNORE_TCCL_PROPERTY = "log4j.ignoreTCL";
47  
48      private static final SecurityManager SECURITY_MANAGER = System.getSecurityManager();
49  
50      // this variable must be lazily loaded; otherwise, we get a nice circular class loading problem where LoaderUtil
51      // wants to use PropertiesUtil, but then PropertiesUtil wants to use LoaderUtil.
52      private static Boolean ignoreTCCL;
53  
54      private static final boolean GET_CLASS_LOADER_DISABLED;
55  
56      private static final PrivilegedAction<ClassLoader> TCCL_GETTER = new ThreadContextClassLoaderGetter();
57  
58      static {
59          if (SECURITY_MANAGER != null) {
60              boolean getClassLoaderDisabled;
61              try {
62                  SECURITY_MANAGER.checkPermission(new RuntimePermission("getClassLoader"));
63                  getClassLoaderDisabled = false;
64              } catch (final SecurityException ignored) {
65                  getClassLoaderDisabled = true;
66              }
67              GET_CLASS_LOADER_DISABLED = getClassLoaderDisabled;
68          } else {
69              GET_CLASS_LOADER_DISABLED = false;
70          }
71      }
72  
73      private LoaderUtil() {
74      }
75  
76      /**
77       * Gets the current Thread ClassLoader. Returns the system ClassLoader if the TCCL is {@code null}. If the system
78       * ClassLoader is {@code null} as well, then the ClassLoader for this class is returned. If running with a
79       * {@link SecurityManager} that does not allow access to the Thread ClassLoader or system ClassLoader, then the
80       * ClassLoader for this class is returned.
81       *
82       * @return the current ThreadContextClassLoader.
83       */
84      public static ClassLoader getThreadContextClassLoader() {
85          if (GET_CLASS_LOADER_DISABLED) {
86              // we can at least get this class's ClassLoader regardless of security context
87              // however, if this is null, there's really no option left at this point
88              return LoaderUtil.class.getClassLoader();
89          }
90          return SECURITY_MANAGER == null ? TCCL_GETTER.run() : AccessController.doPrivileged(TCCL_GETTER);
91      }
92  
93      /**
94       *
95       */
96      private static class ThreadContextClassLoaderGetter implements PrivilegedAction<ClassLoader> {
97          @Override
98          public ClassLoader run() {
99              final ClassLoader cl = Thread.currentThread().getContextClassLoader();
100             if (cl != null) {
101                 return cl;
102             }
103             final ClassLoader ccl = LoaderUtil.class.getClassLoader();
104             return ccl == null && !GET_CLASS_LOADER_DISABLED ? ClassLoader.getSystemClassLoader() : ccl;
105         }
106     }
107 
108     public static ClassLoader[] getClassLoaders() {
109         List<ClassLoader> classLoaders = new ArrayList<>();
110         ClassLoader tcl = getThreadContextClassLoader();
111         classLoaders.add(tcl);
112         ClassLoader current = LoaderUtil.class.getClassLoader();
113         if (current != tcl) {
114             classLoaders.add(current);
115             ClassLoader parent = current.getParent();
116             while (parent != null && !classLoaders.contains(parent)) {
117                 classLoaders.add(parent);
118             }
119         }
120         ClassLoader parent = tcl;
121         while (parent != null && !classLoaders.contains(parent)) {
122             classLoaders.add(parent);
123         }
124         if (!classLoaders.contains(ClassLoader.getSystemClassLoader())) {
125             classLoaders.add(ClassLoader.getSystemClassLoader());
126         }
127         return classLoaders.toArray(new ClassLoader[classLoaders.size()]);
128     }
129 
130     /**
131      * Determines if a named Class can be loaded or not.
132      *
133      * @param className The class name.
134      * @return {@code true} if the class could be found or {@code false} otherwise.
135      * @since 2.7
136      */
137     public static boolean isClassAvailable(final String className) {
138         try {
139             final Class<?> clazz = loadClass(className);
140             return clazz != null;
141         } catch (final ClassNotFoundException | LinkageError e) {
142             return false;
143         } catch (final Throwable e) {
144             LowLevelLogUtil.logException("Unknown error checking for existence of class: " + className, e);
145             return false;
146         }
147     }
148 
149     /**
150      * Loads a class by name. This method respects the {@link #IGNORE_TCCL_PROPERTY} Log4j property. If this property is
151      * specified and set to anything besides {@code false}, then the default ClassLoader will be used.
152      *
153      * @param className The class name.
154      * @return the Class for the given name.
155      * @throws ClassNotFoundException if the specified class name could not be found
156      * @since 2.1
157      */
158     public static Class<?> loadClass(final String className) throws ClassNotFoundException {
159         if (isIgnoreTccl()) {
160             return Class.forName(className);
161         }
162         try {
163             return getThreadContextClassLoader().loadClass(className);
164         } catch (final Throwable ignored) {
165             return Class.forName(className);
166         }
167     }
168 
169     /**
170      * Loads and instantiates a Class using the default constructor.
171      *
172      * @param clazz The class.
173      * @return new instance of the class.
174      * @throws IllegalAccessException if the class can't be instantiated through a public constructor
175      * @throws InstantiationException if there was an exception whilst instantiating the class
176      * @throws InvocationTargetException if there was an exception whilst constructing the class
177      * @since 2.7
178      */
179     public static <T> T newInstanceOf(final Class<T> clazz)
180             throws InstantiationException, IllegalAccessException, InvocationTargetException {
181         try {
182             return clazz.getConstructor().newInstance();
183         } catch (final NoSuchMethodException ignored) {
184             // FIXME: looking at the code for Class.newInstance(), this seems to do the same thing as above
185             return clazz.newInstance();
186         }
187     }
188 
189     /**
190      * Loads and instantiates a Class using the default constructor.
191      *
192      * @param className The class name.
193      * @return new instance of the class.
194      * @throws ClassNotFoundException if the class isn't available to the usual ClassLoaders
195      * @throws IllegalAccessException if the class can't be instantiated through a public constructor
196      * @throws InstantiationException if there was an exception whilst instantiating the class
197      * @throws NoSuchMethodException if there isn't a no-args constructor on the class
198      * @throws InvocationTargetException if there was an exception whilst constructing the class
199      * @since 2.1
200      */
201     @SuppressWarnings("unchecked")
202     public static <T> T newInstanceOf(final String className) throws ClassNotFoundException, IllegalAccessException,
203             InstantiationException, NoSuchMethodException, InvocationTargetException {
204         return newInstanceOf((Class<T>) loadClass(className));
205     }
206 
207     /**
208      * Loads and instantiates a derived class using its default constructor.
209      *
210      * @param className The class name.
211      * @param clazz The class to cast it to.
212      * @param <T> The type of the class to check.
213      * @return new instance of the class cast to {@code T}
214      * @throws ClassNotFoundException if the class isn't available to the usual ClassLoaders
215      * @throws IllegalAccessException if the class can't be instantiated through a public constructor
216      * @throws InstantiationException if there was an exception whilst instantiating the class
217      * @throws NoSuchMethodException if there isn't a no-args constructor on the class
218      * @throws InvocationTargetException if there was an exception whilst constructing the class
219      * @throws ClassCastException if the constructed object isn't type compatible with {@code T}
220      * @since 2.1
221      */
222     public static <T> T newCheckedInstanceOf(final String className, final Class<T> clazz)
223             throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException,
224             IllegalAccessException {
225         return clazz.cast(newInstanceOf(className));
226     }
227 
228     /**
229      * Loads and instantiates a class given by a property name.
230      *
231      * @param propertyName The property name to look up a class name for.
232      * @param clazz        The class to cast it to.
233      * @param <T>          The type to cast it to.
234      * @return new instance of the class given in the property or {@code null} if the property was unset.
235      * @throws ClassNotFoundException    if the class isn't available to the usual ClassLoaders
236      * @throws IllegalAccessException    if the class can't be instantiated through a public constructor
237      * @throws InstantiationException    if there was an exception whilst instantiating the class
238      * @throws NoSuchMethodException     if there isn't a no-args constructor on the class
239      * @throws InvocationTargetException if there was an exception whilst constructing the class
240      * @throws ClassCastException        if the constructed object isn't type compatible with {@code T}
241      * @since 2.5
242      */
243     public static <T> T newCheckedInstanceOfProperty(final String propertyName, final Class<T> clazz)
244         throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException,
245         IllegalAccessException {
246         final String className = PropertiesUtil.getProperties().getStringProperty(propertyName);
247         if (className == null) {
248             return null;
249         }
250         return newCheckedInstanceOf(className, clazz);
251     }
252 
253     private static boolean isIgnoreTccl() {
254         // we need to lazily initialize this, but concurrent access is not an issue
255         if (ignoreTCCL == null) {
256             final String ignoreTccl = PropertiesUtil.getProperties().getStringProperty(IGNORE_TCCL_PROPERTY, null);
257             ignoreTCCL = ignoreTccl != null && !"false".equalsIgnoreCase(ignoreTccl.trim());
258         }
259         return ignoreTCCL;
260     }
261 
262     /**
263      * Finds classpath {@linkplain URL resources}.
264      *
265      * @param resource the name of the resource to find.
266      * @return a Collection of URLs matching the resource name. If no resources could be found, then this will be empty.
267      * @since 2.1
268      */
269     public static Collection<URL> findResources(final String resource) {
270         final Collection<UrlResource> urlResources = findUrlResources(resource);
271         final Collection<URL> resources = new LinkedHashSet<>(urlResources.size());
272         for (final UrlResource urlResource : urlResources) {
273             resources.add(urlResource.getUrl());
274         }
275         return resources;
276     }
277 
278     static Collection<UrlResource> findUrlResources(final String resource) {
279         final ClassLoader[] candidates = {getThreadContextClassLoader(), LoaderUtil.class.getClassLoader(),
280                 GET_CLASS_LOADER_DISABLED ? null : ClassLoader.getSystemClassLoader()};
281         final Collection<UrlResource> resources = new LinkedHashSet<>();
282         for (final ClassLoader cl : candidates) {
283             if (cl != null) {
284                 try {
285                     final Enumeration<URL> resourceEnum = cl.getResources(resource);
286                     while (resourceEnum.hasMoreElements()) {
287                         resources.add(new UrlResource(cl, resourceEnum.nextElement()));
288                     }
289                 } catch (final IOException e) {
290                     LowLevelLogUtil.logException(e);
291                 }
292             }
293         }
294         return resources;
295     }
296 
297     /**
298      * {@link URL} and {@link ClassLoader} pair.
299      */
300     static class UrlResource {
301         private final ClassLoader classLoader;
302         private final URL url;
303 
304         UrlResource(final ClassLoader classLoader, final URL url) {
305             this.classLoader = classLoader;
306             this.url = url;
307         }
308 
309         public ClassLoader getClassLoader() {
310             return classLoader;
311         }
312 
313         public URL getUrl() {
314             return url;
315         }
316 
317         @Override
318         public boolean equals(final Object o) {
319             if (this == o) {
320                 return true;
321             }
322             if (o == null || getClass() != o.getClass()) {
323                 return false;
324             }
325 
326             final UrlResource that = (UrlResource) o;
327 
328             if (classLoader != null ? !classLoader.equals(that.classLoader) : that.classLoader != null) {
329                 return false;
330             }
331             if (url != null ? !url.equals(that.url) : that.url != null) {
332                 return false;
333             }
334 
335             return true;
336         }
337 
338         @Override
339         public int hashCode() {
340             return Objects.hashCode(classLoader) + Objects.hashCode(url);
341         }
342     }
343 }