Centralize token generation and formats

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=135313726

java/google/registry/util/RandomStringGenerator.java

@@ -0,0 +1,44 @@
+// Copyright 2016 The Domain Registry Authors. All Rights Reserved.
+//
+// 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 google.registry.util;
+
+import static com.google.common.base.Preconditions.checkArgument;
+
+import java.util.Random;
+import javax.inject.Inject;
+import javax.inject.Named;
+
+/** Random string generator. */
+public class RandomStringGenerator extends StringGenerator {
+
+  private final Random random;
+
+  @Inject
+  RandomStringGenerator(@Named("alphabet") String alphabet, Random random) {
+    super(alphabet);
+    this.random = random;
+  }
+
+  /** Generates a random string of a specified length. */
+  @Override
+  public String createString(int length) {
+    checkArgument(length > 0);
+    char[] password = new char[length];
+    for (int i = 0; i < length; ++i) {
+      password[i] = alphabet.charAt(random.nextInt(alphabet.length()));
+    }
+    return new String(password);
+  }
+}