Moved some common classes from dozmod server/client to this lib

1 files changed, 94 insertions, 0 deletions

diff --git a/src/main/java/org/openslx/util/GenericDataCache.java b/src/main/java/org/openslx/util/GenericDataCache.java
new file mode 100644
index 0000000..5852c94
--- /dev/null
+++ b/src/main/java/org/openslx/util/GenericDataCache.java
@@ -0,0 +1,94 @@
+package org.openslx.util;
+
+import java.util.concurrent.atomic.AtomicReference;
+
+import org.apache.log4j.Logger;
+
+public abstract class GenericDataCache<T> {
+	
+	private static final Logger LOGGER = Logger.getLogger(GenericDataCache.class);
+	
+	/**
+	 * How long the cached data is valid after fetching
+	 */
+	private final int validMs;
+	
+	/**
+	 * Deadline when the cache goes invalid
+	 */
+	private long validUntil = 0;
+	
+	/**
+	 * The data being held
+	 */
+	private final AtomicReference<T> item = new AtomicReference<>();
+	
+	public GenericDataCache(int validMs) {
+		this.validMs = validMs;
+	}
+	
+	/**
+	 * Get the cached object, but refresh the cache first if
+	 * the cached instance is too old.
+	 * 
+	 * @return
+	 */
+	public T get() {
+		return get(CacheMode.DEFAULT);
+	}
+	
+	/**
+	 * Get the cached object, using the given cache access strategy.
+	 * ALWAYS_CACHED: Never refresh the cache, except if it has never been fetched before
+	 * DEFAULT: Only fetch from remote if the cached value is too old
+	 * NEVER_CACHED: Always fetch from remote. If it fails, return null
+	 *
+	 * @param mode Cache access strategy as described above 
+	 * @return T
+	 */
+	public T get(CacheMode mode) {
+		switch (mode) {
+		case ALWAYS_CACHED:
+			if (validUntil == 0)
+				ensureUpToDate(true);
+			break;
+		case DEFAULT:
+			ensureUpToDate(false);
+			break;
+		case NEVER_CACHED:
+			if (!ensureUpToDate(true))
+				return null;
+			break;
+		}
+		return item.get();
+	}
+	
+	private synchronized boolean ensureUpToDate(boolean force) {
+		final long now = System.currentTimeMillis();
+		if (!force && now < validUntil)
+			return true;
+		T fetched;
+		try {
+			fetched = update();
+			if (fetched == null)
+				return false;
+		} catch (Exception e) {
+			LOGGER.warn("Could not fetch fresh data", e);
+			return false;
+		}
+		item.set(fetched);
+		validUntil = now + validMs;
+		return true;
+	}
+	
+	protected abstract T update() throws Exception;
+	
+	//
+	
+	public static enum CacheMode {
+		ALWAYS_CACHED,
+		DEFAULT,
+		NEVER_CACHED
+	}
+
+}