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/*
 * Copyright 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 de.odysseus.el.tree;


/**
 * Tree store class.
 * A tree store holds a {@link de.odysseus.el.tree.TreeBuilder} and a
 * {@link de.odysseus.el.tree.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;
	}
}