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diff --git a/java/com/google/gerrit/server/project/RefPattern.java b/java/com/google/gerrit/server/project/RefPattern.java
new file mode 100644
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+++ b/java/com/google/gerrit/server/project/RefPattern.java
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+// Copyright (C) 2016 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.server.project;
+
+import com.google.common.base.Throwables;
+import com.google.common.cache.CacheBuilder;
+import com.google.common.cache.CacheLoader;
+import com.google.common.cache.LoadingCache;
+import com.google.gerrit.common.data.AccessSection;
+import com.google.gerrit.common.data.RefConfigSection;
+import com.google.gerrit.common.errors.InvalidNameException;
+import dk.brics.automaton.RegExp;
+import java.util.concurrent.ExecutionException;
+import java.util.regex.Pattern;
+import java.util.regex.PatternSyntaxException;
+import org.eclipse.jgit.lib.Repository;
+
+public class RefPattern {
+  public static final String USERID_SHARDED = "shardeduserid";
+  public static final String USERNAME = "username";
+
+  private static final LoadingCache<String, String> exampleCache =
+      CacheBuilder.newBuilder()
+          .maximumSize(4000)
+          .build(
+              new CacheLoader<String, String>() {
+                @Override
+                public String load(String refPattern) {
+                  return example(refPattern);
+                }
+              });
+
+  public static String shortestExample(String refPattern) {
+    if (isRE(refPattern)) {
+      try {
+        return exampleCache.get(refPattern);
+      } catch (ExecutionException e) {
+        Throwables.throwIfUnchecked(e.getCause());
+        throw new RuntimeException(e);
+      }
+    } else if (refPattern.endsWith("/*")) {
+      return refPattern.substring(0, refPattern.length() - 1) + '1';
+    } else {
+      return refPattern;
+    }
+  }
+
+  static String example(String refPattern) {
+    // Since Brics will substitute dot [.] with \0 when generating
+    // shortest example, any usage of dot will fail in
+    // Repository.isValidRefName() if not combined with star [*].
+    // To get around this, we substitute the \0 with an arbitrary
+    // accepted character.
+    return toRegExp(refPattern).toAutomaton().getShortestExample(true).replace('\0', '-');
+  }
+
+  public static boolean isRE(String refPattern) {
+    return refPattern.startsWith(AccessSection.REGEX_PREFIX);
+  }
+
+  public static RegExp toRegExp(String refPattern) {
+    if (isRE(refPattern)) {
+      refPattern = refPattern.substring(1);
+    }
+    return new RegExp(refPattern, RegExp.NONE);
+  }
+
+  public static void validate(String refPattern) throws InvalidNameException {
+    if (refPattern.startsWith(RefConfigSection.REGEX_PREFIX)) {
+      if (!Repository.isValidRefName(shortestExample(refPattern))) {
+        throw new InvalidNameException(refPattern);
+      }
+    } else if (refPattern.equals(RefConfigSection.ALL)) {
+      // This is a special case we have to allow, it fails below.
+    } else if (refPattern.endsWith("/*")) {
+      String prefix = refPattern.substring(0, refPattern.length() - 2);
+      if (!Repository.isValidRefName(prefix)) {
+        throw new InvalidNameException(refPattern);
+      }
+    } else if (!Repository.isValidRefName(refPattern)) {
+      throw new InvalidNameException(refPattern);
+    }
+    validateRegExp(refPattern);
+  }
+
+  public static void validateRegExp(String refPattern) throws InvalidNameException {
+    try {
+      refPattern = refPattern.replace("${" + USERID_SHARDED + "}", "");
+      refPattern = refPattern.replace("${" + USERNAME + "}", "");
+      Pattern.compile(refPattern);
+    } catch (PatternSyntaxException e) {
+      throw new InvalidNameException(refPattern + " " + e.getMessage());
+    }
+  }
+}