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/*
 * Based on JUEL 2.2.1 code, 2006-2009 Odysseus Software GmbH
 *
 * 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 org.activiti.engine.impl.juel;

/**
 * Tree store class. A tree store holds a {@link org.activiti.engine.impl.juel.TreeBuilder} and a {@link org.activiti.engine.impl.juel.TreeCache}, provided at construction time. The
 * get(String) method is then used to serve expression trees.
 * 
 * @author Christoph Beck
 */
public class TreeStore {
  private final TreeCache cache;
  private final TreeBuilder builder;

  /**
   * Constructor.
   * 
   * @param builder
   *          the tree builder
   * @param cache
   *          the tree cache (may be null)
   */
  public TreeStore(TreeBuilder builder, TreeCache cache) {
    super();

    this.builder = builder;
    this.cache = cache;
  }

  public TreeBuilder getBuilder() {
    return builder;
  }

  /**
   * Get a {@link Tree}. If a tree for the given expression is present in the cache, it is taken from there; otherwise, the expression string is parsed and the resulting tree is added to the cache.
   * 
   * @param expression
   *          expression string
   * @return expression tree
   */
  public Tree get(String expression) throws TreeBuilderException {
    if (cache == null) {
      return builder.build(expression);
    }
    Tree tree = cache.get(expression);
    if (tree == null) {
      cache.put(expression, tree = builder.build(expression));
    }
    return tree;
  }
}