Java使用Memcached

这些天在设计SNA的架构，接触了一些远程缓存、集群、session复制等的东西，以前做企业应用的时候感觉作用不大，现在设计面对internet的系统架构时就非常有用了，而且在调试后看到压力测试的情况还是比较爽的。 
在缓存的选择上有过很多的思考，虽然说memcached结合java在序列化上性能不怎么样，不过也没有更好的集群环境下的缓存解决方案了，就选择了memcached。本来计划等公司买的服务器到位装个linux再来研究memcached，但这两天在找到了一个windows下的Memcached版本，就动手开始调整现有的框架了。 

windows下的Server端很简单，不用安装，双击运行后默认服务端口是11211，没有试着去更改端口，因为反正以后会用unix版本，到时再记录安装步骤。下载客户端的java API包，接口非常简单，参考API手册上就有现成的例子。 

目标，对旧框架缓存部分进行改造： 
1、缓存工具类 
2、hibernate的provider 
3、用缓存实现session机制 

今天先研究研究缓存工具类的改造，在旧框架中部分函数用了ehcache对执行结果进行了缓存处理，现在目标是提供一个缓存工具类，在配置文件中配置使用哪种缓存（memcached或ehcached），使其它程序对具体的缓存不依赖，同时使用AOP方式来对方法执行结果进行缓存。 
首先是工具类的实现： 
在Spring中配置 

<!-- EhCache Manager -->
<bean id="cacheManager"
    class="org.springframework.cache.ehcache.EhCacheManagerFactoryBean">
    <property name="configLocation">
        <value>classpath:ehcache.xml</value>
    </property>
</bean>

<bean id="localCache"
    class="org.springframework.cache.ehcache.EhCacheFactoryBean">
    <property name="cacheManager" ref="cacheManager" />
    <property name="cacheName"
        value="×××.cache.LOCAL_CACHE" />
</bean>

<bean id="cacheService"
    class="×××.core.cache.CacheService" init-method="init" destroy-method="destory">
    <property name="cacheServerList" value="${cache.servers}"/>
    <property name="cacheServerWeights" value="${cache.cacheServerWeights}"/>
    <property name="cacheCluster" value="${cache.cluster}"/>
    <property name="localCache" ref="localCache"/>
</bean>

在properties文件中配置${cache.servers} ${cache.cacheServerWeights} ${cache.cluster} 
具体工具类的代码 

/**
 * @author Marc
 *
 */
public class CacheService {
    private Log logger = LogFactory.getLog(getClass());

    private Cache localCache;

    String cacheServerList;

    String cacheServerWeights;

    boolean cacheCluster = false;

    int initialConnections = 10;

    int minSpareConnections = 5;

    int maxSpareConnections = 50;

    long maxIdleTime = 1000 * 60 * 30; // 30 minutes

    long maxBusyTime = 1000 * 60 * 5; // 5 minutes

    long maintThreadSleep = 1000 * 5; // 5 seconds

    int socketTimeOut = 1000 * 3; // 3 seconds to block on reads

    int socketConnectTO = 1000 * 3; // 3 seconds to block on initial
                                    // connections. If 0, then will use blocking
                                    // connect (default)

    boolean failover = false; // turn off auto-failover in event of server
                                // down

    boolean nagleAlg = false; // turn off Nagle's algorithm on all sockets in
                                // pool

    MemCachedClient mc;

    public CacheService(){
        mc = new MemCachedClient();
        mc.setCompressEnable(false);
    }
    /**
     * 放入
     *
     */
    public void put(String key, Object obj) {
        Assert.hasText(key);
        Assert.notNull(obj);
        Assert.notNull(localCache);
        if (this.cacheCluster) {
            mc.set(key, obj);
        } else {
            Element element = new Element(key, (Serializable) obj);
            localCache.put(element);
        }
    }
    /**
     * 删除
     */
    public void remove(String key){
        Assert.hasText(key);
        Assert.notNull(localCache);
        if (this.cacheCluster) {
            mc.delete(key);
        }else{
            localCache.remove(key);
        }
    }
    /**
     * 得到
     */
    public Object get(String key) {
        Assert.hasText(key);
        Assert.notNull(localCache);
        Object rt = null;
        if (this.cacheCluster) {
            rt = mc.get(key);
        } else {
            Element element = null;
            try {
                element = localCache.get(key);
            } catch (CacheException cacheException) {
                throw new DataRetrievalFailureException("Cache failure: "
                        + cacheException.getMessage());
            }
            if(element != null)
                rt = element.getValue();
        }
        return rt;
    }
    /**
     * 判断是否存在
     *
     */
    public boolean exist(String key){
        Assert.hasText(key);
        Assert.notNull(localCache);
        if (this.cacheCluster) {
            return mc.keyExists(key);
        }else{
            return this.localCache.isKeyInCache(key);
        }
    }
    private void init() {
        if (this.cacheCluster) {
            String[] serverlist = cacheServerList.split(",");
            Integer[] weights = this.split(cacheServerWeights);
            // initialize the pool for memcache servers
            SockIOPool pool = SockIOPool.getInstance();
            pool.setServers(serverlist);
            pool.setWeights(weights);
            pool.setInitConn(initialConnections);
            pool.setMinConn(minSpareConnections);
            pool.setMaxConn(maxSpareConnections);
            pool.setMaxIdle(maxIdleTime);
            pool.setMaxBusyTime(maxBusyTime);
            pool.setMaintSleep(maintThreadSleep);
            pool.setSocketTO(socketTimeOut);
            pool.setSocketConnectTO(socketConnectTO);
            pool.setNagle(nagleAlg);
            pool.setHashingAlg(SockIOPool.NEW_COMPAT_HASH);
            pool.initialize();
            logger.info("初始化memcached pool!");
        }
    }

    private void destory() {
        if (this.cacheCluster) {
            SockIOPool.getInstance().shutDown();
        }
    }
}

然后实现函数的AOP拦截类，用来在函数执行前返回缓存内容 

public class CachingInterceptor implements MethodInterceptor {

    private CacheService cacheService;
    private String cacheKey;

    public void setCacheKey(String cacheKey) {
        this.cacheKey = cacheKey;
    }

    public void setCacheService(CacheService cacheService) {
        this.cacheService = cacheService;
    }

    public Object invoke(MethodInvocation invocation) throws Throwable {
        Object result = cacheService.get(cacheKey);
        //如果函数返回结果不在Cache中,执行函数并将结果放入Cache
        if (result == null) {
            result = invocation.proceed();
            cacheService.put(cacheKey,result);
        }
        return result;
    }
}

Spring的AOP配置如下： 

<aop:config proxy-target-class="true">
        <aop:advisor
            pointcut="execution(* ×××.PoiService.getOne(..))"
            advice-ref="PoiServiceCachingAdvice" />
    </aop:config>

    <bean id="BasPoiServiceCachingAdvice"
        class="×××.core.cache.CachingInterceptor">
        <property name="cacheKey" value="PoiService" />
        <property name="cacheService" ref="cacheService" />
    </bean>