SchemaEntryCache.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.schemarepo;

/**
 * <p>
 * A {@link SchemaEntryCache} is a bi-directional cache from a schema string to
 * a schema id string. In a given {@link Subject} the mapping between a schema
 * and its id is immutable and can be cached. Other aspects of {@link Subject}
 * are not safe to cache.
 * </p>
 * <p>
 * In a {@link Subject} schemas are Strings and can not be null or empty.
 * See {@link RepositoryUtil#validateSchemaOrSubject(String)}
 * </p>
 * {@link #add(SchemaEntry)}, {@link #lookupById(String)}, and
 * {@link #lookupBySchema(String)} must be thread-safe with respect to
 * each-other.
 */
public interface SchemaEntryCache {

  /**
   * Look up a schema entry by its full string form. Thread-safe.
   *
   * @throws NullPointerException
   *           If the provided schema is null
   */
  SchemaEntry lookupBySchema(String schema);

  /**
   * Look up a schema entry by its id. Thread-safe.
   *
   * @throws NullPointerException
   *           If the provided id is null
   */
  SchemaEntry lookupById(String id);

  /**
   * Add the schema entry to this cache.
   *
   * @param entry
   *          schema entry to add. If the provided entry is null, returns null;
   *
   * @return the {@link SchemaEntry} that is in the cache after the call
   *         completes. If the entry already exists the pre-existing value is
   *         returned, otherwise the value returned is the entry provided. If
   *         the provided entry is null, returns null. Thread-safe.
   */
  SchemaEntry add(SchemaEntry entry);

  /**
   * Creates instances of {@link SchemaEntryCache}<br/>
   * <br/>
   *
   * @see {@link Subject#cacheWith(Subject, SchemaEntryCache)}
   */
  interface Factory {
    /**
     * Create a {@link SchemaEntryCache} instance for use with
     * {@link Subject#cacheWith(Subject, SchemaEntryCache)}.
     *
     * May return null to disable use of a SchemaEntryCache
     */
    SchemaEntryCache createSchemaEntryCache();
  }

}