Java tutorial
package com.limegroup.gnutella.licenses; import java.io.BufferedInputStream; import java.io.BufferedOutputStream; import java.io.File; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.net.URI; import java.util.HashMap; import java.util.Iterator; import java.util.Map; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.limewire.io.IOUtils; import org.limewire.service.ErrorService; import org.limewire.util.CommonUtils; import org.limewire.util.GenericsUtils; import com.google.inject.Singleton; import com.limegroup.gnutella.URN; /** * A repository of licenses. */ @Singleton public class LicenseCache { private static final Log LOG = LogFactory.getLog(LicenseCache.class); /** * The amount of time to keep a license in the cache. */ private static final long EXPIRY_TIME = 7 * 24 * 60 * 60 * 1000; // one week. /** * File where the licenses are serialized. */ private final File CACHE_FILE = new File(CommonUtils.getUserSettingsDir(), "licenses.cache"); /** * A map of Licenses. One License per URI. */ private Map<URI, License> licenses; /** * An extra map of data that Licenses can use * to cache info. This information lasts forever. */ private Map<Object, Object> data; /** * Whether or not data is dirty since the last time we wrote to disk. */ private boolean dirty = false; LicenseCache() { // TODO move this out of construction deserialize(); } /** * Adds a verified license. */ synchronized void addVerifiedLicense(License license) { licenses.put(license.getLicenseURI(), license); dirty = true; } /** * Adds data. */ synchronized void addData(Object key, Object value) { data.put(key, value); dirty = true; } /** * Retrieves the cached license for the specified URI, substituting * the license string for a new one. */ synchronized License getLicense(String licenseString, URI licenseURI) { License license = licenses.get(licenseURI); if (license != null) return license.copy(licenseString, licenseURI); else return null; } /** * Gets details. */ synchronized Object getData(Object key) { return data.get(key); } /** * Determines if the license is verified for the given URN and URI. */ synchronized boolean isVerifiedAndValid(URN urn, URI uri) { License license = licenses.get(uri); return license != null && license.isValid(urn); } /** * Loads values from cache file, if available */ private void deserialize() { ObjectInputStream ois = null; try { if (!CACHE_FILE.exists()) { // finally-block will initialize maps return; } ois = new ObjectInputStream(new BufferedInputStream(new FileInputStream(CACHE_FILE))); Object o = ois.readObject(); if (o != null) licenses = GenericsUtils.scanForMap(o, URI.class, License.class, GenericsUtils.ScanMode.REMOVE); o = ois.readObject(); if (o != null) data = GenericsUtils.scanForMap(o, Object.class, Object.class, GenericsUtils.ScanMode.REMOVE); removeOldEntries(); } catch (Throwable t) { LOG.error("Can't read licenses", t); } finally { IOUtils.close(ois); if (licenses == null) licenses = new HashMap<URI, License>(); if (data == null) data = new HashMap<Object, Object>(); } } /** * Removes any stale entries from the map so that they will automatically * be replaced. */ private void removeOldEntries() { long cutoff = System.currentTimeMillis() - EXPIRY_TIME; // discard outdated info for (Iterator<License> i = licenses.values().iterator(); i.hasNext();) { License license = i.next(); if (license.getLastVerifiedTime() < cutoff) { dirty = true; i.remove(); } } } /** * Write cache so that we only have to calculate them once. */ public synchronized void persistCache() { if (!dirty) return; ObjectOutputStream oos = null; try { oos = new ObjectOutputStream(new BufferedOutputStream(new FileOutputStream(CACHE_FILE))); oos.writeObject(licenses); oos.writeObject(data); oos.flush(); } catch (IOException e) { ErrorService.error(e); } finally { IOUtils.close(oos); } dirty = false; } }