Java tutorial
/** * Licensed to Apereo under one or more contributor license * agreements. See the NOTICE file distributed with this work * for additional information regarding copyright ownership. * Apereo 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 the following location: * * 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.apereo.services.persondir.support.xml; import org.springframework.core.io.Resource; import org.springframework.util.Assert; import javax.xml.bind.JAXBContext; import javax.xml.bind.JAXBException; import javax.xml.bind.Unmarshaller; import java.io.IOException; import java.io.InputStream; /** * Base logic for loading unmarshalling an XML document via JAXB and only reloading the cached object model when needed. * The class attempts to monitor the lastModified date of the {@link Resource} to determine when to reload. If that fails * the resource is reloaded periodically as specified by the {@link #setNoLastModifiedReloadPeriod(long)} property. * * The class determines the return type and the base package to use for the {@link JAXBContext#newInstance(String)} call * via the loadedType parameter provided to the constructor. * * @author Eric Dalquist */ public class CachingJaxbLoaderImpl<T> implements CachingJaxbLoader<T> { protected final Class<T> loadedType; protected long noLastModifiedReloadPeriod = 5 * 60 * 1000; //5 minute default protected Resource mappedXmlResource; protected T unmarshalledObject; protected long lastModifiedTime = Integer.MIN_VALUE; public CachingJaxbLoaderImpl(final Class<T> loadedType) { Assert.notNull(loadedType, "loadedType can not be null"); this.loadedType = loadedType; } public long getNoLastModifiedReloadPeriod() { return noLastModifiedReloadPeriod; } /** * Period between reloads if last-modified of the {@link Resource} cannot be determined * * @param noLastModifiedReloadPeriod period between reloads */ public void setNoLastModifiedReloadPeriod(final long noLastModifiedReloadPeriod) { this.noLastModifiedReloadPeriod = noLastModifiedReloadPeriod; } public Resource getMappedXmlResource() { return mappedXmlResource; } /** * The XML resource to load. * * @param mappedXmlResource XML resource to load */ public void setMappedXmlResource(final Resource mappedXmlResource) { this.mappedXmlResource = mappedXmlResource; } /* (non-Javadoc) * @see org.jasig.services.persondir.support.xml.CachingJaxbLoader#getUnmarshalledObject() */ @Override public T getUnmarshalledObject() { return this.getUnmarshalledObject(null); } /* (non-Javadoc) * @see org.jasig.services.persondir.support.xml.CachingJaxbLoader#getUnmarshalledObject(org.jasig.services.persondir.support.xml.CachingJaxbLoader.UnmarshallingCallback) */ @Override public T getUnmarshalledObject(final UnmarshallingCallback<T> callback) { //Only bother checking for a change if the object already exists Long lastModified = null; if (this.unmarshalledObject != null) { lastModified = this.getLastModified(); //Return immediately if nothing has changed if (this.isCacheValid(lastModified)) { return this.unmarshalledObject; } } final InputStream xmlInputStream = this.getXmlInputStream(); final JAXBContext jaxbContext = this.getJAXBContext(); final Unmarshaller unmarshaller = this.getUnmarshaller(jaxbContext); final T unmarshalledObject = this.unmarshal(xmlInputStream, unmarshaller); if (callback != null) { callback.postProcessUnmarshalling(unmarshalledObject); } this.unmarshalledObject = unmarshalledObject; if (lastModified != null) { this.lastModifiedTime = lastModified; } else { this.lastModifiedTime = System.currentTimeMillis(); } return this.unmarshalledObject; } /** * @return The last modified date for the XML file, null if it cannot be determined */ protected Long getLastModified() { try { return this.mappedXmlResource.lastModified(); } catch (final IOException ioe) { return null; } } /** * Determines if the cached unmarshalled object is still valid * * @param lastModified last modified timestamp of the resource, null if not known. * @return true if the cached object should be used */ protected boolean isCacheValid(final Long lastModified) { return (lastModified != null && lastModified <= this.lastModifiedTime) || (lastModified == null && (this.lastModifiedTime + this.noLastModifiedReloadPeriod) <= System.currentTimeMillis()); } /** * @return The InputStream to read the XML file from */ protected InputStream getXmlInputStream() { final InputStream xmlInputStream; try { xmlInputStream = this.mappedXmlResource.getInputStream(); } catch (final IOException e) { throw new RuntimeException("Failed to open InputStream for Resource: " + this.mappedXmlResource, e); } return xmlInputStream; } /** * @return The JAXB context to parse the XML resource with */ protected JAXBContext getJAXBContext() { final Package loadedPackage = this.loadedType.getPackage(); final String filterDisplayPackage = loadedPackage.getName(); try { return JAXBContext.newInstance(filterDisplayPackage); } catch (final JAXBException e) { throw new RuntimeException("Failed to create " + JAXBContext.class + " to unmarshal " + this.loadedType, e); } } /** * @param jaxbContext The context to get an unmarshaller for * @return An unmarshaller to use to generate object from the XML */ protected Unmarshaller getUnmarshaller(final JAXBContext jaxbContext) { try { return jaxbContext.createUnmarshaller(); } catch (final JAXBException e) { throw new RuntimeException( "Failed to create " + Unmarshaller.class + " to unmarshal " + this.loadedType, e); } } /** * @param xmlInputStream InputStream to read the XML from * @param unmarshaller Unmarshaller to generate the object from the XML with * @return An unmarshalled object model of the XML */ @SuppressWarnings("unchecked") protected T unmarshal(final InputStream xmlInputStream, final Unmarshaller unmarshaller) { try { return (T) unmarshaller.unmarshal(xmlInputStream); } catch (final JAXBException e) { throw new RuntimeException("Unexpected JAXB error while unmarshalling " + this.mappedXmlResource, e); } } }