SourceProviders


1   /**
2    * Copyright (C) 2006 Google Inc.
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    * http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  
17  package com.google.inject.spi;
18  
19  import java.util.Collections  ;
20  import java.util.HashSet  ;
21  import java.util.Set  ;
22  
23  /**
24   * Provides access to the default {@link SourceProvider} implementation and
25   * common controls for certain implementations.
26   * 
27   * @author crazybob@google.com (Bob Lee)
28   */
29  public class SourceProviders {
30  
31    private SourceProviders() {}
32  
33    public static final Object   UNKNOWN_SOURCE = "[unknown source]";
34    
35    static final SourceProvider DEFAULT_INSTANCE = new StacktraceSourceProvider();
36  
37    static Set  <String  > skippedClassNames = Collections.emptySet();
38  
39    static {
40      skip(SourceProviders.class);
41      skip(StacktraceSourceProvider.class);
42    }
43  
44    /**
45     * Instructs stacktrace-based providers to skip the given class in the stack
46     * trace when determining the source. Use this to keep the binder from
47     * logging utility methods as the sources of bindings (i.e. it will skip to
48     * the utility methods' callers instead).
49     *
50     * <p>Skipping only takes place after this method is called.
51     */
52    public synchronized static void skip(Class  <?> clazz) {
53      Set  <String  > copy = new HashSet  <String  >();
54      copy.addAll(skippedClassNames);
55      copy.add(clazz.getName());
56      skippedClassNames = Collections.unmodifiableSet(copy);
57    }
58  
59    /**
60     * Gets the set of class names which should be skipped by stacktrace-based
61     * providers.
62     */
63    public synchronized static Set  <String  > getSkippedClassNames() {
64      return skippedClassNames;
65    }
66  
67    static ThreadLocal  <SourceProvider[]> localSourceProvider =
68        new ThreadLocal  <SourceProvider[]>() {
69      protected SourceProvider[] initialValue() {
70        return new SourceProvider[] { DEFAULT_INSTANCE };
71      }
72    };
73  
74    /**
75     * Returns the current source obtained from the default provider.
76     */
77    public static Object   defaultSource() {
78      return localSourceProvider.get()[0].source();
79    }
80  
81    /**
82     * Sets the default source provider, runs the given command, and then
83     * restores the previous default source provider.
84     */
85    public static void withDefault(
86        SourceProvider sourceProvider, Runnable   r) {
87      // We use a holder so we perform only 1 thread local access instead of 3.
88      SourceProvider[] holder = localSourceProvider.get();
89      SourceProvider previous = holder[0];
90      try {
91        holder[0] = sourceProvider;
92        r.run();
93      } finally {
94        holder[0] = previous;
95      }
96    }
97  
98    static class StacktraceSourceProvider implements SourceProvider {
99      public Object   source() {
100       // Search up the stack until we find a class outside of this one.
101       Set  <String  > skippedClassNames = getSkippedClassNames();
102       for (final StackTraceElement   element : new Throwable  ().getStackTrace()) {
103         String   className = element.getClassName();
104         if (!skippedClassNames.contains(className)) {
105           return element;
106         }
107       }
108       throw new AssertionError  ();
109     }
110   }
111 }
112
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