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/*
 * 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.apache.struts2.result.xslt;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

import javax.servlet.ServletContext;
import javax.xml.transform.Source;
import javax.xml.transform.TransformerException;
import javax.xml.transform.URIResolver;
import javax.xml.transform.stream.StreamSource;
import java.io.InputStream;

/**
 * ServletURIResolver is a URIResolver that can retrieve resources from the servlet context using the scheme "response".
 * e.g.
 * 
 * A URI resolver is called when a stylesheet uses an xsl:include, xsl:import, or document() function to find the
 * resource (file).
 */
public class ServletURIResolver implements URIResolver {

    private static final Logger LOG = LogManager.getLogger(ServletURIResolver.class);

    private static final String PROTOCOL = "response:";

    private final ServletContext servletContext;

    public ServletURIResolver(ServletContext servletContext) {
        this.servletContext = servletContext;
    }

    public Source resolve(String href, String base) throws TransformerException {
        LOG.debug("ServletURIResolver resolve(): href={}, base={}", href, base);
        if (href.startsWith(PROTOCOL)) {
            String res = href.substring(PROTOCOL.length());
            LOG.debug("Resolving resource <{}>", res);

            InputStream is = servletContext.getResourceAsStream(res);

            if (is == null) {
                throw new TransformerException(
                    "Resource " + res + " not found in resources.");
            }

            return new StreamSource(is);
        }

        throw new TransformerException(
            "Cannot handle protocol of resource " + href);
    }
}