View Javadoc
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.net.URL;
21  import java.util.Collection;
22  import java.util.Enumeration;
23  import java.util.HashSet;
24  import java.util.Properties;
25  import java.util.concurrent.locks.Lock;
26  import java.util.concurrent.locks.ReentrantLock;
27  
28  import org.apache.logging.log4j.Logger;
29  import org.apache.logging.log4j.spi.Provider;
30  import org.apache.logging.log4j.status.StatusLogger;
31  
32  /**
33   * <em>Consider this class private.</em>
34   * Utility class for Log4j {@link Provider}s. When integrating with an application container framework, any Log4j
35   * Providers not accessible through standard classpath scanning should {@link #loadProvider(java.net.URL, ClassLoader)}
36   * a classpath accordingly.
37   */
38  public final class ProviderUtil {
39  
40      /**
41       * Resource name for a Log4j 2 provider properties file.
42       */
43      protected static final String PROVIDER_RESOURCE = "META-INF/log4j-provider.properties";
44      private static final String API_VERSION = "Log4jAPIVersion";
45  
46      private static final String[] COMPATIBLE_API_VERSIONS = {
47          "2.0.0", "2.1.0"
48      };
49  
50      private static final Logger LOGGER = StatusLogger.getLogger();
51  
52      protected static final Collection<Provider> PROVIDERS = new HashSet<Provider>();
53  
54      /**
55       * Guards the ProviderUtil singleton instance from lazy initialization. This is primarily used for OSGi support.
56       *
57       * @since 2.1
58       */
59      protected static final Lock STARTUP_LOCK = new ReentrantLock();
60      // STARTUP_LOCK guards INSTANCE for lazy initialization; this allows the OSGi Activator to pause the startup and
61      // wait for a Provider to be installed. See LOG4J2-373
62      private static volatile ProviderUtil INSTANCE;
63  
64      private ProviderUtil() {
65          for (LoaderUtil.UrlResource resource : LoaderUtil.findUrlResources(PROVIDER_RESOURCE)) {
66              loadProvider(resource.getUrl(), resource.getClassLoader());
67          }
68      }
69  
70      /**
71       * Loads an individual Provider implementation. This method is really only useful for the OSGi bundle activator
72       * and this class itself.
73       *
74       * @param url the URL to the provider properties file
75       * @param cl the ClassLoader to load the provider classes with
76       */
77      protected static void loadProvider(final URL url, final ClassLoader cl) {
78          try {
79              final Properties props = PropertiesUtil.loadClose(url.openStream(), url);
80              if (validVersion(props.getProperty(API_VERSION))) {
81                  PROVIDERS.add(new Provider(props, url, cl));
82              }
83          } catch (final IOException e) {
84              LOGGER.error("Unable to open {}", url, e);
85          }
86      }
87  
88      /**
89       * @deprecated Use {@link #loadProvider(java.net.URL, ClassLoader)} instead. Will be removed in 3.0.
90       */
91      @Deprecated
92      protected static void loadProviders(final Enumeration<URL> urls, final ClassLoader cl) {
93          if (urls != null) {
94              while (urls.hasMoreElements()) {
95                  loadProvider(urls.nextElement(), cl);
96              }
97          }
98      }
99  
100     public static Iterable<Provider> getProviders() {
101         lazyInit();
102         return PROVIDERS;
103     }
104 
105     public static boolean hasProviders() {
106         lazyInit();
107         return !PROVIDERS.isEmpty();
108     }
109 
110     /**
111      * Lazily initializes the ProviderUtil singleton.
112      *
113      * @since 2.1
114      */
115     protected static void lazyInit() {
116         //noinspection DoubleCheckedLocking
117         if (INSTANCE == null) {
118             try {
119                 STARTUP_LOCK.lockInterruptibly();
120                 if (INSTANCE == null) {
121                     INSTANCE = new ProviderUtil();
122                 }
123             } catch (final InterruptedException e) {
124                 LOGGER.fatal("Interrupted before Log4j Providers could be loaded.", e);
125                 Thread.currentThread().interrupt();
126             } finally {
127                 STARTUP_LOCK.unlock();
128             }
129         }
130     }
131 
132     public static ClassLoader findClassLoader() {
133         return LoaderUtil.getThreadContextClassLoader();
134     }
135 
136     private static boolean validVersion(final String version) {
137         for (final String v : COMPATIBLE_API_VERSIONS) {
138             if (version.startsWith(v)) {
139                 return true;
140             }
141         }
142         return false;
143     }
144 }