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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.getParent();
121         while (parent != null && !classLoaders.contains(parent)) {
122             classLoaders.add(parent);
123             parent = parent.getParent();
124         }
125         if (!classLoaders.contains(ClassLoader.getSystemClassLoader())) {
126             classLoaders.add(ClassLoader.getSystemClassLoader());
127         }
128         return classLoaders.toArray(new ClassLoader[classLoaders.size()]);
129     }
130 
131     /**
132      * Determines if a named Class can be loaded or not.
133      *
134      * @param className The class name.
135      * @return {@code true} if the class could be found or {@code false} otherwise.
136      * @since 2.7
137      */
138     public static boolean isClassAvailable(final String className) {
139         try {
140             final Class<?> clazz = loadClass(className);
141             return clazz != null;
142         } catch (final ClassNotFoundException | LinkageError e) {
143             return false;
144         } catch (final Throwable e) {
145             LowLevelLogUtil.logException("Unknown error checking for existence of class: " + className, e);
146             return false;
147         }
148     }
149 
150     /**
151      * Loads a class by name. This method respects the {@link #IGNORE_TCCL_PROPERTY} Log4j property. If this property is
152      * specified and set to anything besides {@code false}, then the default ClassLoader will be used.
153      *
154      * @param className The class name.
155      * @return the Class for the given name.
156      * @throws ClassNotFoundException if the specified class name could not be found
157      * @since 2.1
158      */
159     public static Class<?> loadClass(final String className) throws ClassNotFoundException {
160         if (isIgnoreTccl()) {
161             return Class.forName(className);
162         }
163         try {
164             return getThreadContextClassLoader().loadClass(className);
165         } catch (final Throwable ignored) {
166             return Class.forName(className);
167         }
168     }
169 
170     /**
171      * Loads and instantiates a Class using the default constructor.
172      *
173      * @param clazz The class.
174      * @return new instance of the class.
175      * @throws IllegalAccessException if the class can't be instantiated through a public constructor
176      * @throws InstantiationException if there was an exception whilst instantiating the class
177      * @throws InvocationTargetException if there was an exception whilst constructing the class
178      * @since 2.7
179      */
180     public static <T> T newInstanceOf(final Class<T> clazz)
181             throws InstantiationException, IllegalAccessException, InvocationTargetException {
182         try {
183             return clazz.getConstructor().newInstance();
184         } catch (final NoSuchMethodException ignored) {
185             // FIXME: looking at the code for Class.newInstance(), this seems to do the same thing as above
186             return clazz.newInstance();
187         }
188     }
189 
190     /**
191      * Loads and instantiates a Class using the default constructor.
192      *
193      * @param className The class name.
194      * @return new instance of the class.
195      * @throws ClassNotFoundException if the class isn't available to the usual ClassLoaders
196      * @throws IllegalAccessException if the class can't be instantiated through a public constructor
197      * @throws InstantiationException if there was an exception whilst instantiating the class
198      * @throws NoSuchMethodException if there isn't a no-args constructor on the class
199      * @throws InvocationTargetException if there was an exception whilst constructing the class
200      * @since 2.1
201      */
202     @SuppressWarnings("unchecked")
203     public static <T> T newInstanceOf(final String className) throws ClassNotFoundException, IllegalAccessException,
204             InstantiationException, NoSuchMethodException, InvocationTargetException {
205         return newInstanceOf((Class<T>) loadClass(className));
206     }
207 
208     /**
209      * Loads and instantiates a derived class using its default constructor.
210      *
211      * @param className The class name.
212      * @param clazz The class to cast it to.
213      * @param <T> The type of the class to check.
214      * @return new instance of the class cast to {@code T}
215      * @throws ClassNotFoundException if the class isn't available to the usual ClassLoaders
216      * @throws IllegalAccessException if the class can't be instantiated through a public constructor
217      * @throws InstantiationException if there was an exception whilst instantiating the class
218      * @throws NoSuchMethodException if there isn't a no-args constructor on the class
219      * @throws InvocationTargetException if there was an exception whilst constructing the class
220      * @throws ClassCastException if the constructed object isn't type compatible with {@code T}
221      * @since 2.1
222      */
223     public static <T> T newCheckedInstanceOf(final String className, final Class<T> clazz)
224             throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException,
225             IllegalAccessException {
226         return clazz.cast(newInstanceOf(className));
227     }
228 
229     /**
230      * Loads and instantiates a class given by a property name.
231      *
232      * @param propertyName The property name to look up a class name for.
233      * @param clazz        The class to cast it to.
234      * @param <T>          The type to cast it to.
235      * @return new instance of the class given in the property or {@code null} if the property was unset.
236      * @throws ClassNotFoundException    if the class isn't available to the usual ClassLoaders
237      * @throws IllegalAccessException    if the class can't be instantiated through a public constructor
238      * @throws InstantiationException    if there was an exception whilst instantiating the class
239      * @throws NoSuchMethodException     if there isn't a no-args constructor on the class
240      * @throws InvocationTargetException if there was an exception whilst constructing the class
241      * @throws ClassCastException        if the constructed object isn't type compatible with {@code T}
242      * @since 2.5
243      */
244     public static <T> T newCheckedInstanceOfProperty(final String propertyName, final Class<T> clazz)
245         throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException,
246         IllegalAccessException {
247         final String className = PropertiesUtil.getProperties().getStringProperty(propertyName);
248         if (className == null) {
249             return null;
250         }
251         return newCheckedInstanceOf(className, clazz);
252     }
253 
254     private static boolean isIgnoreTccl() {
255         // we need to lazily initialize this, but concurrent access is not an issue
256         if (ignoreTCCL == null) {
257             final String ignoreTccl = PropertiesUtil.getProperties().getStringProperty(IGNORE_TCCL_PROPERTY, null);
258             ignoreTCCL = ignoreTccl != null && !"false".equalsIgnoreCase(ignoreTccl.trim());
259         }
260         return ignoreTCCL;
261     }
262 
263     /**
264      * Finds classpath {@linkplain URL resources}.
265      *
266      * @param resource the name of the resource to find.
267      * @return a Collection of URLs matching the resource name. If no resources could be found, then this will be empty.
268      * @since 2.1
269      */
270     public static Collection<URL> findResources(final String resource) {
271         final Collection<UrlResource> urlResources = findUrlResources(resource);
272         final Collection<URL> resources = new LinkedHashSet<>(urlResources.size());
273         for (final UrlResource urlResource : urlResources) {
274             resources.add(urlResource.getUrl());
275         }
276         return resources;
277     }
278 
279     static Collection<UrlResource> findUrlResources(final String resource) {
280         // @formatter:off
281         final ClassLoader[] candidates = {
282                 getThreadContextClassLoader(), 
283                 LoaderUtil.class.getClassLoader(),
284                 GET_CLASS_LOADER_DISABLED ? null : ClassLoader.getSystemClassLoader()};
285         // @formatter:on
286         final Collection<UrlResource> resources = new LinkedHashSet<>();
287         for (final ClassLoader cl : candidates) {
288             if (cl != null) {
289                 try {
290                     final Enumeration<URL> resourceEnum = cl.getResources(resource);
291                     while (resourceEnum.hasMoreElements()) {
292                         resources.add(new UrlResource(cl, resourceEnum.nextElement()));
293                     }
294                 } catch (final IOException e) {
295                     LowLevelLogUtil.logException(e);
296                 }
297             }
298         }
299         return resources;
300     }
301 
302     /**
303      * {@link URL} and {@link ClassLoader} pair.
304      */
305     static class UrlResource {
306         private final ClassLoader classLoader;
307         private final URL url;
308 
309         UrlResource(final ClassLoader classLoader, final URL url) {
310             this.classLoader = classLoader;
311             this.url = url;
312         }
313 
314         public ClassLoader getClassLoader() {
315             return classLoader;
316         }
317 
318         public URL getUrl() {
319             return url;
320         }
321 
322         @Override
323         public boolean equals(final Object o) {
324             if (this == o) {
325                 return true;
326             }
327             if (o == null || getClass() != o.getClass()) {
328                 return false;
329             }
330 
331             final UrlResource that = (UrlResource) o;
332 
333             if (classLoader != null ? !classLoader.equals(that.classLoader) : that.classLoader != null) {
334                 return false;
335             }
336             if (url != null ? !url.equals(that.url) : that.url != null) {
337                 return false;
338             }
339 
340             return true;
341         }
342 
343         @Override
344         public int hashCode() {
345             return Objects.hashCode(classLoader) + Objects.hashCode(url);
346         }
347     }
348 }