src/com/google/enterprise/secmgr/config/ConfigSingleton.java

// Copyright 2008 Google Inc.
//
// 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.enterprise.secmgr.config;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

import java.util.Observable;
import java.util.Observer;
import java.util.logging.Logger;

import javax.annotation.concurrent.GuardedBy;
import javax.annotation.concurrent.ThreadSafe;

/**
 * A singleton class to access configured parameters.
 */
@ThreadSafe
public class ConfigSingleton {
  private static final Logger LOGGER = Logger.getLogger(ConfigSingleton.class.getName());

  private static ConfigSingleton instance;
  @GuardedBy("class") private static Gson gson;
  private static final LocalObservable observable = new LocalObservable();

  private static final class LocalObservable extends Observable {
    @Override
    protected void setChanged() {
      super.setChanged();
    }
  }

  private ConfigSingleton() {
    resetInternal();
  }

  @VisibleForTesting
  public static synchronized void reset() {
    instance.resetInternal();
  }

  private synchronized void resetInternal() {
  }

  /**
   * Adds an observer that's notified of config changes.
   */
  public static void addObserver(Observer observer) {
    observable.addObserver(observer);
  }

  /**
   * Gets an observable that's notified of config changes.
   */
  public static Observable getObservable() {
    return observable;
  }

  static void setChanged() {
    observable.setChanged();
    observable.notifyObservers();
  }

  public static synchronized void setGsonRegistrations(GsonRegistrations registrations) {
    GsonBuilder builder = new GsonBuilder();
    builder.setPrettyPrinting();
    registrations.register(builder);
    gson = builder.create();
  }

  /** A type to use for passing in Gson registrations. */
  public interface GsonRegistrations {
    public void register(GsonBuilder builder);
  }

  public static synchronized Gson getGson() {
    Preconditions.checkNotNull(gson);
    return gson;
  }
}