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Minor Description
The ReferenceResolver class allows user to specify what Apache SIS should do when its unmarshal an element defined only by a link to an on-line document. Current implementation does nothing. As a side effect of SIS-345 work, an implementation resolving all links were provided by Image Matters. The code has been extracted in this task for allowing to handle SIS-345 (upgrade to ISO 19115-3) and this task separately.
package org.apache.sis.xml; import java.io.IOException; import java.net.HttpURLConnection; import java.net.MalformedURLException; import java.net.URL; import javax.xml.bind.JAXBException; import javax.xml.bind.Unmarshaller; import org.apache.sis.util.Version; import org.apache.sis.xml.MarshalContext; import org.apache.sis.xml.MarshallerPool; import org.apache.sis.xml.ReferenceResolver; import org.apache.sis.xml.XLink; import org.apache.sis.xml.XML; /** * This class is used to resolve external references in ISO metadata when unmarshalling. * It will <em>always</em> attempt to resolve external references, and will return null * if it fails to do so. * * @author Cullen Rombach (Image Matters) */ public class AllReferenceResolver extends ReferenceResolver { private Version metadataVersion; private MarshallerPool pool; /** * Constructor. * * @param metadataVersion the version of metadata to unmarshal (e.g. ISO 19139) */ public AllReferenceResolver(Version metadataVersion) throws JAXBException { super(); this.metadataVersion = metadataVersion; } @Override public <T> T resolve(MarshalContext context, Class<T> type, XLink link) { T content = super.resolve(context, type, link); try { if (content == null) { // Cast the URI in the XLink to a URL. URL href = link.getHRef().toURL(); // Used for storing a redirect URL if necessary. URL newHref = href; // Flag to see if a redirect is necessary. Boolean redirect = true; while (redirect) { // Only check for redirects on HTTP and HTTPS connections. if (newHref.getProtocol().contains("http")) { // Open a connection to the URL to check for a redirect if it uses HTTP protocol. HttpURLConnection connection = (HttpURLConnection) newHref.openConnection(); // Check HTTP status for a possible redirect. int status = connection.getResponseCode(); // If we need to redirect, do so. if (status == HttpURLConnection.HTTP_MOVED_TEMP || status == HttpURLConnection.HTTP_MOVED_PERM || status == HttpURLConnection.HTTP_SEE_OTHER) { // If we need to redirect, get the new URL. newHref = new URL(connection.getHeaderField("Location")); } // Otherwise, flag that no redirect is necessary. else { redirect = false; } } // If the link doesn't use HTTP protocol, don't check for a redirect. else { redirect = false; } } // Build an Unmarshaller (and the MarshallerPool it belongs to). Unmarshaller unmarshaller = acquireUnmarshaller(metadataVersion); // If there was a redirect, unmarshal the new URL. if (!newHref.equals(href)) { content = type.cast(unmarshaller.unmarshal(newHref)); pool.recycle(unmarshaller); } // Otherwise, unmarshal the original URL. else if (href != null) { content = type.cast(unmarshaller.unmarshal(href)); pool.recycle(unmarshaller); } } // If any sort of exception occurred, just return whatever the parent class found. } catch (MalformedURLException e) { return content; } catch (JAXBException e) { return content; } catch (IOException e) { return content; } return content; } /** * Get an unmarshaller with its own AllReferenceResolver that operates on the given metadata version. * * @return a new Unmarshaller. */ private Unmarshaller acquireUnmarshaller(Version metadataVersion) throws JAXBException { pool = new MarshallerPool(null); Unmarshaller unmarshaller = pool.acquireUnmarshaller(); // Set metadata version for unmarshalling. unmarshaller.setProperty(XML.METADATA_VERSION, metadataVersion); // Set resolver for external references. unmarshaller.setProperty(XML.RESOLVER, new AllReferenceResolver(metadataVersion)); return unmarshaller; } }
