uk.ac.ed.ph.snuggletex.utilities.ClassPathURIResolver Maven / Gradle / Ivy

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/* $Id: ClassPathURIResolver.java 525 2010-01-05 14:07:36Z davemckain $
 *
 * Copyright (c) 2010, The University of Edinburgh.
 * All Rights Reserved
 */
package uk.ac.ed.ph.snuggletex.utilities;

import java.io.InputStream;
import java.net.URI;
import java.net.URISyntaxException;

import javax.xml.transform.Source;
import javax.xml.transform.TransformerException;
import javax.xml.transform.URIResolver;
import javax.xml.transform.stream.StreamSource;

/**
 * Trivial implementation of {@link URIResolver} that looks for resources via the {@link
 * ClassLoader}.
 *
 * Such resources should be specified via a special URI scheme called {@link #URI_SCHEME}, i.e.
 * of the form classpath:/uk/ac/ed/ph/snuggletex/thingy.xsl.
 *
 * (The '/' is required here, unlike the similar mechanism in Spring Framework.)
 *
 * @author David McKain
 * @version $Revision: 525 $
 */
public final class ClassPathURIResolver implements URIResolver {

  public static final String URI_SCHEME = "classpath";

  private static final ClassPathURIResolver singletonInstance = new ClassPathURIResolver();

  private ClassPathURIResolver() {
    /* (We'll make this a singleton as it is stateless) */
  }

  public static ClassPathURIResolver getInstance() {
    return singletonInstance;
  }

  public Source resolve(String href, String base) throws TransformerException {
    /* Handle the special document('') case as normal */
    if (href.equals("")) {
      return null;
    }

    /* Resolve href against base URI */
    URI baseUri;
    try {
      baseUri = new URI(base);
    } catch (URISyntaxException e) {
      throw new TransformerException("Could not convert base=" + base + " into a URI", e);
    }
    URI resolvedUri = baseUri.resolve(href);

    /* See if it's one of our URI schemes. If so, resolve */
    Source result = null;
    if (URI_SCHEME.equals(resolvedUri.getScheme())) {
      /* Strip off the leading '/' from the path */
      String resourceLocation = resolvedUri.getPath().substring(1);
      InputStream resourceStream =
          getClass().getClassLoader().getResourceAsStream(resourceLocation);
      if (resourceStream != null) {
        result = new StreamSource(resourceStream, resolvedUri.toString());
      } else {
        throw new TransformerException(
            "Could not load resource at " + resourceLocation + " via ClassLoader");
      }
    }
    return result;
  }
}