基于memcached for java 实现通用分布式缓存和集群分布式缓存

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));
}
}
}