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Add caching ability for SAX EntityResolver.
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furfurylic
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Mar 3, 2016
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,241 @@ | ||
| /* | ||
| * Chionographis | ||
| * | ||
| * These codes are licensed under CC0. | ||
| * https://creativecommons.org/publicdomain/zero/1.0/deed | ||
| */ | ||
|
|
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| package net.furfurylic.chionographis; | ||
|
|
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| import java.io.ByteArrayInputStream; | ||
| import java.io.ByteArrayOutputStream; | ||
| import java.io.DataInputStream; | ||
| import java.io.File; | ||
| import java.io.FileInputStream; | ||
| import java.io.IOException; | ||
| import java.io.InputStream; | ||
| import java.net.URI; | ||
| import java.nio.file.Paths; | ||
| import java.util.Collections; | ||
| import java.util.IdentityHashMap; | ||
| import java.util.Map; | ||
| import java.util.Optional; | ||
| import java.util.WeakHashMap; | ||
| import java.util.function.Consumer; | ||
| import java.util.function.Function; | ||
|
|
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| import javax.xml.parsers.DocumentBuilder; | ||
| import javax.xml.parsers.DocumentBuilderFactory; | ||
| import javax.xml.parsers.ParserConfigurationException; | ||
| import javax.xml.transform.Source; | ||
| import javax.xml.transform.TransformerException; | ||
| import javax.xml.transform.URIResolver; | ||
| import javax.xml.transform.dom.DOMSource; | ||
|
|
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| import org.w3c.dom.Document; | ||
| import org.xml.sax.EntityResolver; | ||
| import org.xml.sax.InputSource; | ||
| import org.xml.sax.SAXException; | ||
|
|
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| final class CachingResolver implements EntityResolver, URIResolver { | ||
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| private static final Object LOCK = new Object(); | ||
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| private static Map<URI, URI> canonicalizedURIsForBytes_; | ||
| private static Map<URI, Optional<byte[]>> bytes_; | ||
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| private static Map<URI, URI> canonicalizedURIsForSources_; | ||
| private static Map<URI, Optional<Source>> sources_; | ||
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| Consumer<URI> listenStored_; | ||
| Consumer<URI> listenHit_; | ||
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| public CachingResolver(Consumer<URI> listenStored, Consumer<URI> listenHit) { | ||
| listenStored_ = listenStored; | ||
| listenHit_ = listenHit; | ||
| } | ||
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| @Override | ||
| public InputSource resolveEntity(String publicId, String systemId) | ||
| throws SAXException, IOException { | ||
| if (systemId == null) { | ||
| return null; | ||
| } | ||
| URI uri = URI.create(systemId); | ||
| uri = uniquifyURI(uri); | ||
| if (uri == null) { | ||
| return null; | ||
| } | ||
|
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| synchronized (LOCK) { | ||
| if (bytes_ == null) { | ||
| canonicalizedURIsForBytes_ = Collections.synchronizedMap(new WeakHashMap<URI, URI>()); | ||
| bytes_ = Collections.synchronizedMap(new IdentityHashMap<>()); | ||
| } | ||
| } | ||
|
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| Optional<byte[]> cached = accessCache(uri, canonicalizedURIsForBytes_, bytes_, u -> { | ||
| try { | ||
| if (u.getScheme().toLowerCase().equals("file")) { | ||
| File file = new File(u); | ||
| long length = file.length(); | ||
| if (length <= Integer.MAX_VALUE) { | ||
| byte[] content = new byte[(int) length]; | ||
| try (DataInputStream in = new DataInputStream(new FileInputStream(file))) { | ||
| in.readFully(content); | ||
| } | ||
| return content; | ||
| } | ||
| } | ||
| byte[] buffer = new byte[4096]; | ||
| ByteArrayOutputStream bytes = new ByteArrayOutputStream(); | ||
| try (InputStream in = u.toURL().openStream()) { | ||
| int length; | ||
| while ((length = in.read(buffer)) != -1) { | ||
| bytes.write(buffer, 0, length); | ||
| } | ||
| } | ||
| return bytes.toByteArray(); | ||
| } catch (IOException e) { | ||
| return null; | ||
| } | ||
| }); | ||
|
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| if (cached.isPresent()) { | ||
| InputSource inputSource = new InputSource(new ByteArrayInputStream(cached.get())); | ||
| inputSource.setSystemId(systemId); | ||
| inputSource.setPublicId(publicId); | ||
| return inputSource; | ||
| } else { | ||
| return null; | ||
| } | ||
| } | ||
|
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| @Override | ||
| public Source resolve(String href, String base) throws TransformerException { | ||
| URI uri; | ||
| if (base == null) { | ||
| uri = URI.create(href); | ||
| } else { | ||
| uri = URI.create(base).resolve(href); | ||
| } | ||
| uri = uniquifyURI(uri); | ||
| if (uri == null) { | ||
| return null; | ||
| } | ||
|
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| synchronized (LOCK) { | ||
| if (sources_ == null) { | ||
| canonicalizedURIsForSources_ = Collections.synchronizedMap(new WeakHashMap<URI, URI>()); | ||
| sources_ = Collections.synchronizedMap(new IdentityHashMap<>()); | ||
| } | ||
| } | ||
|
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| Optional<Source> cached = accessCache(uri, canonicalizedURIsForSources_, sources_, u -> { | ||
| DocumentBuilderFactory dbfac = DocumentBuilderFactory.newInstance(); | ||
| dbfac.setNamespaceAware(true); | ||
| try { | ||
| DocumentBuilder builder = dbfac.newDocumentBuilder(); | ||
| builder.setEntityResolver(this); | ||
| Document document = builder.parse(u.toString()); | ||
| return new DOMSource(document, u.toString()); | ||
| } catch (ParserConfigurationException | SAXException | IOException e) { | ||
| return null; | ||
| } | ||
| }); | ||
| return cached.orElse(null); | ||
| } | ||
|
|
||
| /** | ||
| * Normalizes a URI in terms of its logical content. | ||
| * | ||
| * @param uri | ||
| * a URI to normalize. | ||
| * | ||
| * @return | ||
| * the normalized URI. | ||
| */ | ||
| private static URI uniquifyURI(URI uri) { | ||
| if (!uri.isAbsolute()) { | ||
| return null; | ||
| } | ||
| if (uri.getScheme().toLowerCase().equals("file")) { | ||
| // Afraid that omission of "xx/../" may break path meanings for symbolic links | ||
| try { | ||
| uri = Paths.get(uri).toRealPath().toUri(); | ||
| } catch (IOException e) { | ||
| return null; | ||
| } | ||
| } else { | ||
| uri = uri.normalize(); | ||
| } | ||
| return uri; | ||
| } | ||
|
|
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| /** | ||
| * | ||
| * @param uri | ||
| * a URI. | ||
| * @param canonicalURIs | ||
| * @param cache | ||
| * a possibly identity-based synchronized map. | ||
| * @param factory | ||
| * a factory function which make an object from a URI. | ||
| * | ||
| * @return | ||
| * a possibly-empty resolved object. | ||
| */ | ||
| private <T> Optional<T> accessCache(URI uri, Map<URI, URI> canonicalURIs, Map<URI, Optional<T>> cache, Function<URI, ? extends T> factory) { | ||
| // Get the canonicalized form | ||
| URI canonicalizedURI = canonicalizeURI(uri, canonicalURIs); | ||
|
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| // From here uri shall not be in the canonicalized form | ||
| if (canonicalizedURI == uri) { | ||
| uri = URI.create(uri.toString()); | ||
| } | ||
|
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| // Lock with privately-canonicalized form | ||
| synchronized (canonicalizedURI) { | ||
| Optional<T> cached = cache.get(canonicalizedURI); | ||
| if (cached != null) { | ||
| if (!cached.isPresent()) { | ||
| // Means that an error occurred in the previous try. | ||
| return null; | ||
| } else { | ||
| // Cache hit. | ||
| listenHit_.accept(uri); | ||
| } | ||
| } else { | ||
| cached = Optional.<T>ofNullable(factory.apply(uri)); | ||
| if (cached.isPresent()) { | ||
| listenStored_.accept(uri); | ||
| } | ||
| cache.put(canonicalizedURI, cached); | ||
| } | ||
| return cached; | ||
| } | ||
| } | ||
|
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| /** | ||
| * Canonicalizes a URI so that URIs which have the same logical content are one same object. | ||
| * | ||
| * @param uri | ||
| * a URI to canonicalize. | ||
| * @param canonicalURIs | ||
| * a canonicalization mapping for URIs. | ||
| * | ||
| * @return | ||
| * the canonicalized form of the URI, | ||
| * which is different object from the parameter <i>uri</i> | ||
| * if it did not come from this method. | ||
| */ | ||
| private static URI canonicalizeURI(URI uri, Map<URI, URI> canonicalURIs) { | ||
| assert uri != null; | ||
| URI existing = canonicalURIs.putIfAbsent(uri, uri); | ||
| if (existing == null) { | ||
| return uri; | ||
| } else { | ||
| return existing; | ||
| } | ||
| } | ||
| } |
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