Java tutorial
package com.limegroup.gnutella.auth; 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.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.util.CommonUtils; import org.limewire.util.GenericsUtils; import com.limegroup.gnutella.URN; /** * A repository of content responses. */ class ContentCache { private static final Log LOG = LogFactory.getLog(ContentCache.class); /** The amount of time to keep a response 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(), "responses.cache"); /** Map of SHA1 to Responses. */ private Map<URN, ContentResponseData> responses = new HashMap<URN, ContentResponseData>(); /** Whether or not data is dirty since the last time we wrote to disk. */ private boolean dirty = false; /** Returns the number of items in the map. */ synchronized int getSize() { return responses.size(); } /** Determines if there is a response for the given URN. */ synchronized boolean hasResponseFor(URN urn) { return responses.containsKey(urn); } /** Adds the given response for the given URN. */ synchronized void addResponse(URN urn, ContentResponseData response) { responses.put(urn, response); dirty = true; } /** Gets the response for the given URN. */ synchronized ContentResponseData getResponse(URN urn) { return responses.get(urn); } /** Initializes this cache. */ synchronized void initialize() { dirty = false; deserialize(); } /** Writes to disk. */ synchronized void writeToDisk() { if (dirty) persistCache(); dirty = false; } /** * Loads values from cache file, if available. */ private void deserialize() { long cutoff = System.currentTimeMillis() - EXPIRY_TIME; ObjectInputStream ois = null; try { ois = new ObjectInputStream(new BufferedInputStream(new FileInputStream(CACHE_FILE))); Map map = (Map) ois.readObject(); Map<URN, ContentResponseData> checked = GenericsUtils.scanForMap(map, URN.class, ContentResponseData.class, GenericsUtils.ScanMode.REMOVE); if (checked.size() != map.size()) dirty = true; for (Iterator<ContentResponseData> i = checked.values().iterator(); i.hasNext();) { ContentResponseData data = i.next(); if (data.getCreationTime() < cutoff) { if (LOG.isWarnEnabled()) LOG.warn("Removing old response [" + data + "]"); i.remove(); dirty = true; } } responses = checked; } catch (Throwable t) { dirty = true; LOG.error("Can't read responses", t); } finally { IOUtils.close(ois); if (responses == null) responses = new HashMap<URN, ContentResponseData>(); } } /** * Write cache so that we only have to calculate them once. */ public void persistCache() { ObjectOutputStream oos = null; try { oos = new ObjectOutputStream(new BufferedOutputStream(new FileOutputStream(CACHE_FILE))); oos.writeObject(responses); oos.flush(); } catch (IOException e) { LOG.error(e); } finally { IOUtils.close(oos); } } }