com.jillesvangurp.xmltools.XPathExpressionCache.java Source code

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Here is the source code for com.jillesvangurp.xmltools.XPathExpressionCache.java

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/**
 * Copyright (c) 2012, Jilles van Gurp
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package com.jillesvangurp.xmltools;

import java.util.Iterator;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;

import javax.xml.namespace.NamespaceContext;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;

import com.google.common.cache.Cache;
import com.google.common.cache.CacheBuilder;

public class XPathExpressionCache {

    private final Cache<String, XPathExpression> cache;

    private final XPath xpath;

    public XPathExpressionCache(int cacheSize, int evictionOfUnusedInMinutes) {
        cache = CacheBuilder.newBuilder().concurrencyLevel(1).maximumSize(cacheSize)
                .expireAfterAccess(evictionOfUnusedInMinutes, TimeUnit.MINUTES).build();
        final XPathFactory xpf = XPathFactory.newInstance();
        xpath = xpf.newXPath();
        xpath.setNamespaceContext(new NamespaceContext() {

            @Override
            public String getNamespaceURI(String prefix) {
                // hack to keep xpath happy
                return "http://domain.com/" + prefix;
            }

            @Override
            @SuppressWarnings("rawtypes")
            public Iterator getPrefixes(String val) {
                // Dummy implementation - not used!
                return null;
            }

            @Override
            public String getPrefix(String uri) {
                // Dummy implementation - not used!
                return null;
            }
        });
    }

    public XPathExpression getExpression(final String expression) throws XPathExpressionException {
        try {
            return cache.get(expression, new Callable<XPathExpression>() {
                @Override
                public XPathExpression call() throws Exception {
                    return xpath.compile(expression);
                }
            });
        } catch (ExecutionException e) {
            if (e.getCause() instanceof XPathExpressionException) {
                throw (XPathExpressionException) e.getCause();
            } else {
                throw new IllegalStateException(e.getCause());
            }
        }
    }
}