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diff --git a/java/com/google/gerrit/lucene/CustomMappingAnalyzer.java b/java/com/google/gerrit/lucene/CustomMappingAnalyzer.java
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+// Copyright (C) 2014 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.lucene;
+
+import java.io.Reader;
+import java.util.Map;
+import org.apache.lucene.analysis.Analyzer;
+import org.apache.lucene.analysis.AnalyzerWrapper;
+import org.apache.lucene.analysis.charfilter.MappingCharFilter;
+import org.apache.lucene.analysis.charfilter.NormalizeCharMap;
+
+/**
+ * This analyzer can be used to provide custom char mappings.
+ *
+ * <p>Example usage:
+ *
+ * <pre class="prettyprint">{@code
+ * Map<String,String> customMapping = new HashMap<>();
+ * customMapping.put("_", " ");
+ * customMapping.put(".", " ");
+ *
+ * CustomMappingAnalyzer analyzer =
+ *   new CustomMappingAnalyzer(new StandardAnalyzer(version), customMapping);
+ * }</pre>
+ */
+public class CustomMappingAnalyzer extends AnalyzerWrapper {
+  private Analyzer delegate;
+  private Map<String, String> customMappings;
+
+  public CustomMappingAnalyzer(Analyzer delegate, Map<String, String> customMappings) {
+    super(delegate.getReuseStrategy());
+    this.delegate = delegate;
+    this.customMappings = customMappings;
+  }
+
+  @Override
+  protected Analyzer getWrappedAnalyzer(String fieldName) {
+    return delegate;
+  }
+
+  @Override
+  protected Reader wrapReader(String fieldName, Reader reader) {
+    NormalizeCharMap.Builder builder = new NormalizeCharMap.Builder();
+    for (Map.Entry<String, String> e : customMappings.entrySet()) {
+      builder.add(e.getKey(), e.getValue());
+    }
+    return new MappingCharFilter(builder.build(), reader);
+  }
+}