本文参考借鉴：http://guazi.iteye.com/blog/107164

前提：基于memcached client for java 的基础进行的二次封装，实现缓存存储的两种模式：通用分布式缓存和集群分布式缓存。以下是对于memcached client for Java 二次封装的UML图。

对于memcached的客户端初始化在CacheFactory中通过读取配置文件cacheConfig.xml完成。通用分布式缓存，只是一个简单的封装，利用memcached client for java提供的分布式支持来实现，这里主要说一下clusterCache的实现思想：对存入的缓存对象的key值进行一次hash，找到对应的服务器存入，然后根据一定的规则再次进行hash，找到另外一个不同的服务器存入，取缓存时，先对要取的key值进行一次hash，找到主服务器，如果获取失败或者获取到的值为null，就对key进行再次hash，找到其从服务器，从这台服务器取缓存结果（如果取到结果就异步的更新到主服务器），这样就形成了主从式集群缓存。特点是：没有绝对的主节点和从节点，正常情况下所有服务器共同承担缓存服务器，在一台服务器出现异常时其他服务器共同承担增加的访问压力。

拓扑结构如下：

源代码

package com.yx.cache;

public interface Cache<T> {
	/**
	 * 获取缓存中的数据
	 * 
	 * @param key
	 * @return
	 */
	T get(String key);

	/**
	 * 把数据放入缓存 如果存在与key对应的值，则返回失败
	 * 
	 * @param key
	 * @param value
	 * @return
	 */
	boolean add(String key, T value);

	/**
	 * 把数据放入缓存 如果存在与key对应的值，则覆盖原有的值
	 * 
	 * @param key
	 * @param value
	 * @return
	 */
	boolean set(String key, T value);

	/**
	 * 缓存更新 如果不存在与key对应的缓存值，则不更新
	 * 
	 * @param key
	 * @param value
	 * @return
	 */
	boolean update(String key, T value);

	/**
	 * 删除缓存
	 * 
	 * @param key
	 * @return
	 */
	boolean delete(String key);
}

通用分布式缓存实现类：

package com.yx.cache;

import com.danga.MemCached.MemCachedClient;

public class CommonCache<T> implements Cache<T> {
	private static MemCachedClient memCachedClient = null;

	private String base = null;

	CommonCache(Class<T> t, MemCachedClient client) {
		memCachedClient = client;
		base = t.getSimpleName() + "-";
	}

	public T get(String key) {
		return (T) memCachedClient.get(base + key);
	}

	public boolean set(String key, T value) {
		return memCachedClient.set(base + key, value);
	}

	@Override
	public boolean update(String key, T value) {
		return memCachedClient.replace(base + key, value);
	}

	@Override
	public boolean delete(String key) {
		return memCachedClient.delete(base + key);
	}

	@Override
	public boolean add(String key, T value) {
		return memCachedClient.add(base + key, value);
	}
}

集群分布式缓存实现类

package com.yx.cache;

import com.danga.MemCached.MemCachedClient;
import com.schooner.MemCached.SchoonerSockIOPool;
import com.yx.cache.util.HashCodeUtil;
import com.yx.task.ThreadPoolManager;

public class ClusterCache<T> implements Cache<T> {
	private static MemCachedClient memCachedClient = null;

	private static ThreadPoolManager taskManager = ThreadPoolManager
			.getInstance("cache");

	private String base = null;

	private SchoonerSockIOPool pool = SchoonerSockIOPool.getInstance();

	ClusterCache(Class<T> t, MemCachedClient client) {
		memCachedClient = client;
		base = "i-" + t.getSimpleName() + "-";
	}

	@Override
	public T get(String key) {
		T value = null;
		if (key == null) {
			return null;
		}
		key = base + key;
		if (pool.getServers().length < 2) {
			value = (T) memCachedClient.get(key);
		} else {
			int hashCode = HashCodeUtil.getHash(key);

			value = (T) memCachedClient.get(key, hashCode);
			if (value == null) {
				hashCode = this.getRehashCode(key, hashCode);

				value = (T) memCachedClient.get(key, hashCode);
				if (value != null) {// 如果在另外一台服务器上取到了缓存，则恢复第一台服务器
					UpdateTask task = new UpdateTask(key, value);
					taskManager.submit(task);
				}

			}
		}
		return value;
	}

	@Override
	public boolean set(String key, T value) {
		if (key == null) {
			return false;
		}
		key = base + key;
		boolean result = false;
		if (pool.getServers().length < 2) {
			result = memCachedClient.set(key, value);
		} else {
			int hashCode = HashCodeUtil.getHash(key);

			result = memCachedClient.set(key, value, hashCode);
			// if (result) {
			hashCode = getRehashCode(key, hashCode);
			memCachedClient.set(key, value, hashCode);

			// }
		}
		return result;
	}

	private int getRehashCode(String key, int oldHashcode) {
		String host = pool.getHost(key, oldHashcode);
		int rehashTries = 0;
		// if (result) {
		int hashCode = HashCodeUtil.getHash(rehashTries + key);
		while (host.equals(pool.getHost(key, hashCode))) {
			rehashTries++;
			hashCode = HashCodeUtil.getHash(rehashTries + key);
		}
		return hashCode;
	}

	@Override
	public boolean update(String key, T value) {
		if (key == null) {
			return false;
		}
		key = base + key;
		boolean result = false;
		if (pool.getServers().length < 2) {
			result = memCachedClient.replace(key, value);
		} else {
			int hashCode = HashCodeUtil.getHash(key);

			result = memCachedClient.replace(key, value, hashCode);
			// if (result) {
			hashCode = getRehashCode(key, hashCode);
			memCachedClient.replace(key, value, hashCode);

			// }
		}
		return result;
	}

	@Override
	public boolean delete(String key) {
		if (key == null) {
			return false;
		}
		key = base + key;
		boolean result = false;
		if (pool.getServers().length < 2) {
			result = memCachedClient.delete(key);
		} else {
			int hashCode = HashCodeUtil.getHash(key);

			result = memCachedClient.delete(key, hashCode, null);
			// if (result) {
			hashCode = this.getRehashCode(key, hashCode);

			memCachedClient.delete(key, hashCode, null);

			// }
		}
		return result;
	}

	@Override
	public boolean add(String key, T value) {
		if (key == null) {
			return false;
		}
		key = base + key;
		boolean result = false;
		if (pool.getServers().length < 2) {
			result = memCachedClient.add(key, value);
		} else {
			int hashCode = HashCodeUtil.getHash(key);

			result = memCachedClient.add(key, value, hashCode);
			// if (result) {
			hashCode = getRehashCode(key, hashCode);
			memCachedClient.add(key, value, hashCode);

			// }
		}
		return result;
	}

	static class UpdateTask implements Runnable {

		private String key;
		private Object value;

		UpdateTask(String key, Object value) {
			this.key = key;
			this.value = value;
		}

		@Override
		public void run() {
			memCachedClient.set(key, value, HashCodeUtil.getHash(key));
		}

	}
}

基于工厂模式创建memcached 存储模式（通用模式还是集群模式）

package com.yx.cache;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import com.danga.MemCached.MemCachedClient;
import com.danga.MemCached.SockIOPool;
import com.yx.cache.util.ConfigUtil;

public class CacheFactory {
	private static MemCachedClient memCachedClient = null;

	@SuppressWarnings("rawtypes")
	private static final Map<String, Cache> map = new ConcurrentHashMap<String, Cache>();

	static {
		String serverStr = ConfigUtil.getConfigValue("servers", "");

		List<String> servers = new ArrayList<String>();
		for (String s : serverStr.split(",")) {
			s = s.trim();
			if (!"".equals(s)) {
				servers.add(s);
			}
		}
		if (servers.size() < 1) {
			throw new RuntimeException("cache 初始化失败！");
		}
		SockIOPool pool = SockIOPool.getInstance();
		pool.setServers(servers.toArray(new String[] {}));
		pool.setFailover(Boolean.valueOf(ConfigUtil.getConfigValue("failover",
				"true")));
		pool.setInitConn(Integer.valueOf(ConfigUtil.getConfigValue("initConn",
				"100")));
		pool.setMinConn(Integer.valueOf(ConfigUtil.getConfigValue("minConn",
				"25")));
		pool.setMaxConn(Integer.valueOf(ConfigUtil.getConfigValue("maxConn",
				"250")));
		pool.setMaintSleep(Integer.valueOf(ConfigUtil.getConfigValue(
				"maintSleep", "30")));
		pool.setNagle(Boolean.valueOf(ConfigUtil.getConfigValue("nagle",
				"false")));// 关闭nagle算法
		pool.setSocketTO(Integer.valueOf(ConfigUtil.getConfigValue("socketTO",
				"3000")));
		pool.setAliveCheck(Boolean.valueOf(ConfigUtil.getConfigValue(
				"aliveCheck", "true")));
		pool.setHashingAlg(Integer.valueOf(ConfigUtil.getConfigValue(
				"hashingAlg", "0")));
		pool.setSocketConnectTO(Integer.valueOf(ConfigUtil.getConfigValue(
				"socketConnectTO", "3000")));
		String wStr = ConfigUtil.getConfigValue("weights", "");
		List<Integer> weights = new ArrayList<Integer>();
		for (String s : wStr.split(",")) {
			s = s.trim();
			if (!"".equals(s)) {
				weights.add(Integer.valueOf(s));

			}
		}
		if (weights.size() == servers.size()) {
			pool.setWeights(weights.toArray(new Integer[] {}));
		}
		pool.initialize();
		memCachedClient = new MemCachedClient();

	}

	public static <T> Cache<T> getCommonCache(Class<T> t) {
		Cache<T> cache = map.get(t.getName());
		if (cache == null) {
			cache = createCommonCache(t);
		}
		return cache;
	}

	public static <T> Cache<T> getClusterCache(Class<T> t) {
		Cache<T> cache = map.get("i-" + t.getName());
		if (cache == null) {
			cache = createClusterCache(t);
		}
		return cache;
	}

	private static synchronized <T> Cache<T> createCommonCache(Class<T> t) {
		Cache<T> cache = map.get(t.getName());
		if (cache == null) {
			cache = new CommonCache<T>(t, memCachedClient);
			map.put(t.getName(), cache);
		}
		return cache;
	}

	private static synchronized <T> Cache<T> createClusterCache(Class<T> t) {
		Cache<T> cache = map.get(t.getName());
		if (cache == null) {
			cache = new ClusterCache<T>(t, memCachedClient);
			map.put(t.getName(), cache);
		}
		return cache;
	}
}

读取配置文件工具类封装和生成Hash代码工具类

ConfigUtil.Java和HashCodeUtil.java

package com.yx.cache.util;

import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;

public class ConfigUtil {

	private static final String CONFILE = "cacheConfig.xml";
	private static final Map<String, String> map = new HashMap<String, String>();

	static {
		SAXReader saxReader = new SAXReader();
		InputStream ins = ConfigUtil.class.getClassLoader()
				.getResourceAsStream(CONFILE);
		try {
			if (ins != null) {
				Document doc = saxReader.read(ins);
				Element root = doc.getRootElement();
				Iterator<Element> iter = root.elementIterator();
				while (iter.hasNext()) {
					Element e = iter.next();
					map.put(e.getName(), e.getTextTrim());
				}
			}
		} catch (DocumentException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			throw new RuntimeException("找不到配置文件：" + CONFILE);
		} finally {
			try {
				if (ins != null) {
					ins.close();
				} else {
					throw new RuntimeException("找不到配置文件：" + CONFILE);
				}
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}

	public static String getConfigValue(String key, String defaultValue) {
		String tmp = map.get(key);
		return isEmpty(tmp) ? defaultValue : tmp;
	}

	public static void main(String[] args) {
		System.out.println(map);
	}

	private static boolean isEmpty(String str) {
		if (str == null || "".equals(str)) {
			return true;
		}
		return false;
	}
}

package com.yx.cache.util;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.zip.CRC32;

import com.schooner.MemCached.SchoonerSockIOPool;

public class HashCodeUtil {

	public static final int NATIVE_HASH = 0; // native String.hashCode();
	public static final int OLD_COMPAT_HASH = 1; // original compatibility
	public static final int NEW_COMPAT_HASH = 2; // new CRC32 based
	public static final int CONSISTENT_HASH = 3; // MD5 Based -- Stops

	private static int hashingAlg = SchoonerSockIOPool.getInstance()
			.getHashingAlg();

	/**
	 * Returns a bucket to check for a given key.
	 * 
	 * @param key
	 *            String key cache is stored under
	 * @return int bucket
	 */
	public static final int getHash(String key) {

		switch (hashingAlg) {
		case NATIVE_HASH:
			return key.hashCode();
		case OLD_COMPAT_HASH:
			return origCompatHashingAlg(key);
		case NEW_COMPAT_HASH:
			return newCompatHashingAlg(key);
		case CONSISTENT_HASH:
			return md5HashingAlg(key);
		default:
			// use the native hash as a default
			hashingAlg = NATIVE_HASH;
			return key.hashCode();
		}
	}

	private static int origCompatHashingAlg(String key) {
		int hash = 0;
		char[] cArr = key.toCharArray();

		for (int i = 0; i < cArr.length; ++i) {
			hash = (hash * 33) + cArr[i];
		}

		return hash;
	}

	private static int newCompatHashingAlg(String key) {
		CRC32 checksum = new CRC32();
		checksum.update(key.getBytes());
		int crc = (int) checksum.getValue();
		return (crc >> 16) & 0x7fff;
	}

	private static int md5HashingAlg(String key) {
		MessageDigest md5 = MD5.get();
		md5.reset();
		md5.update(key.getBytes());
		byte[] bKey = md5.digest();
		int res = ((bKey[3] & 0xFF) << 24) | ((bKey[2] & 0xFF) << 16)
				| ((bKey[1] & 0xFF) << 8) | (bKey[0] & 0xFF);
		return res;
	}

	private static ThreadLocal<MessageDigest> MD5 = new ThreadLocal<MessageDigest>() {
		@Override
		protected final MessageDigest initialValue() {
			try {
				return MessageDigest.getInstance("MD5");
			} catch (NoSuchAlgorithmException e) {
				throw new IllegalStateException(" no md5 algorythm found");
			}
		}
	};

}

对于集群分布式缓存还缺少一个工具类ThreadPoolManage.java

package com.yx.task;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;

/**
 * @author liuyuxiao
 * @Date 2011-5-30 下午04:34:16
 */
public class ThreadPoolManager {

	private static final Map<String, ThreadPoolManager> map = new HashMap<String, ThreadPoolManager>();

	final int CORE_SIZE = 5;

	private ThreadPoolExecutor executor = (ThreadPoolExecutor) Executors
			.newFixedThreadPool(CORE_SIZE);

	public void submit(Runnable task) {
		executor.submit(task);
	}

	public boolean finished() {
		return executor.getCompletedTaskCount() == executor.getTaskCount();
	}

	private ThreadPoolManager() {

	}

	public static synchronized ThreadPoolManager getInstance(String key) {
		ThreadPoolManager t = map.get(key);
		if (t == null) {
			t = new ThreadPoolManager();
			map.put(key, t);
		}
		return t;
	}
}

对于集群缓存模式和通用缓存模式测试：

package com.yx.cache.test;

import com.yx.cache.Cache;
import com.yx.cache.CacheFactory;

public class TestCommonCache {

	/**
	 * @param args
	 */
	public static void main(String[] args) {

		Cache<String> cache = CacheFactory.getCommonCache(String.class);
		int count = 0;
		for (int i = 0; i < 100; i++) {

			// cache.set("" + i, "Hello!" + i);

			String result = cache.get("" + i);
			// System.out.println(String.format("set( %d ): %s", i, success));
			if (result == null) {
				count++;
			}
			System.out.println(String.format("get( %d ): %s", i, result));
		}

		System.out.println(count);
		// for (int i = 0; i < 500; i++) {
		// MemTask task = new MemTask();
		// Thread t = new Thread(task);
		// t.start();
		// }

	}
}

package com.yx.cache.test;

import com.yx.cache.Cache;
import com.yx.cache.CacheFactory;

public class TestClusterCache {

	public static void main(String[] args) {
		Cache<String> cache = CacheFactory.getClusterCache(String.class);
		int count = 0;
		for (int i = 0; i < 100; i++) {

			// cache.set("" + i, "Hello!" + i);

			String result = cache.get("" + i);
			// System.out.println(String.format("set( %d ): %s", i, success));
			if (result == null) {
				count++;
			}
			System.out.println(String.format("get( %d ): %s", i, result));
		}
	}
}