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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.core.lookup;
18  
19  import java.util.HashMap;
20  import java.util.Map;
21  
22  import org.apache.logging.log4j.Logger;
23  import org.apache.logging.log4j.core.LogEvent;
24  import org.apache.logging.log4j.core.config.plugins.util.PluginManager;
25  import org.apache.logging.log4j.core.config.plugins.util.PluginType;
26  import org.apache.logging.log4j.core.util.Loader;
27  import org.apache.logging.log4j.status.StatusLogger;
28  
29  /**
30   * The Interpolator is a StrLookup that acts as a proxy for all the other StrLookups.
31   */
32  public class Interpolator implements StrLookup {
33  
34      private static final Logger LOGGER = StatusLogger.getLogger();
35  
36      /** Constant for the prefix separator. */
37      private static final char PREFIX_SEPARATOR = ':';
38  
39      private final Map<String, StrLookup> lookups = new HashMap<String, StrLookup>();
40  
41      private final StrLookup defaultLookup;
42  
43      public Interpolator(final StrLookup defaultLookup) {
44          this.defaultLookup = defaultLookup == null ? new MapLookup(new HashMap<String, String>()) : defaultLookup;
45          final PluginManager manager = new PluginManager("Lookup");
46          manager.collectPlugins();
47          final Map<String, PluginType<?>> plugins = manager.getPlugins();
48  
49          for (final Map.Entry<String, PluginType<?>> entry : plugins.entrySet()) {
50              @SuppressWarnings("unchecked")
51              final Class<? extends StrLookup> clazz = (Class<? extends StrLookup>) entry.getValue().getPluginClass();
52              try {
53                  lookups.put(entry.getKey(), clazz.getConstructor().newInstance());
54              } catch (final Exception ex) {
55                  LOGGER.error("Unable to create Lookup for {}", entry.getKey(), ex);
56              }
57          }
58      }
59  
60      /**
61       * Create the default Interpolator using only Lookups that work without an event.
62       */
63      public Interpolator() {
64          this((Map<String, String>) null);
65      }
66  
67      /**
68       * Create the dInterpolator using only Lookups that work without an event and initial properties.
69       */
70      public Interpolator(final Map<String, String> properties) {
71          this.defaultLookup = new MapLookup(properties == null ? new HashMap<String, String>() : properties);
72          // TODO: this ought to use the PluginManager
73          lookups.put("sys", new SystemPropertiesLookup());
74          lookups.put("env", new EnvironmentLookup());
75          lookups.put("jndi", new JndiLookup());
76          lookups.put("date", new DateLookup());
77          lookups.put("ctx", new ContextMapLookup());
78          if (Loader.isClassAvailable("javax.servlet.ServletContext")) {
79              try {
80                  lookups.put("web",
81                      Loader.newCheckedInstanceOf("org.apache.logging.log4j.web.WebLookup", StrLookup.class));
82              } catch (final Exception ignored) {
83                  LOGGER.info("Log4j appears to be running in a Servlet environment, but there's no log4j-web module " +
84                      "available. If you want better web container support, please add the log4j-web JAR to your " +
85                      "web archive or server lib directory.");
86              }
87          } else {
88              LOGGER.debug("Not in a ServletContext environment, thus not loading WebLookup plugin.");
89          }
90      }
91  
92       /**
93       * Resolves the specified variable. This implementation will try to extract
94       * a variable prefix from the given variable name (the first colon (':') is
95       * used as prefix separator). It then passes the name of the variable with
96       * the prefix stripped to the lookup object registered for this prefix. If
97       * no prefix can be found or if the associated lookup object cannot resolve
98       * this variable, the default lookup object will be used.
99       *
100      * @param var the name of the variable whose value is to be looked up
101      * @return the value of this variable or <b>null</b> if it cannot be
102      * resolved
103      */
104     @Override
105     public String lookup(final String var) {
106         return lookup(null, var);
107     }
108 
109     /**
110      * Resolves the specified variable. This implementation will try to extract
111      * a variable prefix from the given variable name (the first colon (':') is
112      * used as prefix separator). It then passes the name of the variable with
113      * the prefix stripped to the lookup object registered for this prefix. If
114      * no prefix can be found or if the associated lookup object cannot resolve
115      * this variable, the default lookup object will be used.
116      *
117      * @param event The current LogEvent or null.
118      * @param var the name of the variable whose value is to be looked up
119      * @return the value of this variable or <b>null</b> if it cannot be
120      * resolved
121      */
122     @Override
123     public String lookup(final LogEvent event, String var) {
124         if (var == null) {
125             return null;
126         }
127 
128         final int prefixPos = var.indexOf(PREFIX_SEPARATOR);
129         if (prefixPos >= 0) {
130             final String prefix = var.substring(0, prefixPos);
131             final String name = var.substring(prefixPos + 1);
132             final StrLookup lookup = lookups.get(prefix);
133             String value = null;
134             if (lookup != null) {
135                 value = event == null ? lookup.lookup(name) : lookup.lookup(event, name);
136             }
137 
138             if (value != null) {
139                 return value;
140             }
141             var = var.substring(prefixPos + 1);
142         }
143         if (defaultLookup != null) {
144             return event == null ? defaultLookup.lookup(var) : defaultLookup.lookup(event, var);
145         }
146         return null;
147     }
148 
149     @Override
150     public String toString() {
151         final StringBuilder sb = new StringBuilder();
152         for (final String name : lookups.keySet()) {
153             if (sb.length() == 0) {
154                 sb.append('{');
155             } else {
156                 sb.append(", ");
157             }
158 
159             sb.append(name);
160         }
161         if (sb.length() > 0) {
162             sb.append('}');
163         }
164         return sb.toString();
165     }
166 }