memcached java client 3.0.2详解

memcached-java-client-3.0.2详解

一：MemCachedClient的创建

创建该客户端对象的构造方法有以下几个：
1,

/** * Creates a new instance of MemCachedClient. */ public MemCachedClient() { this(null, true, false); }

2,

/** * Creates a new instance of MemCachedClient accepting a passed in pool * name. * * @param poolName * name of SockIOPool */ public MemCachedClient(String poolName) { this(poolName, true, false); }

3,

/** * Create memcached client. * * @param poolName * name of SockIOPool * @param isTCP * use tcp protocol * @param binaryProtocal * use binary protocol. */ public MemCachedClient(String poolName, boolean isTcp, boolean binaryProtocal) { if (binaryProtocal) client = new BinaryClient(poolName); else client = isTcp ? new AscIIClient(poolName) : new AscIIUDPClient(poolName); }

我们常用的构造方法是1,2两种，从代码可知，我们真正创建的客户端对象大多是AscIIClient.

其客户端的继承关系如下：




而在每一个子类里面的构造方法中都会调用内部的void init()方法来初始化状态。
AscIIClient的init方法实现如下：

/** * Initializes client object to defaults. * * This enables compression and sets compression threshhold to 15 KB. */ private void init() { this.sanitizeKeys = true; //key值是否被编码URLEncoder.encode this.primitiveAsString = false; this.compressEnable = false; this.compressThreshold = COMPRESS_THRESH; this.defaultEncoding = "UTF-8"; this.poolName = (this.poolName == null) ? "default" : this.poolName; // get a pool instance to work with for the life of this instance this.pool = SchoonerSockIOPool.getInstance(poolName); }

AscIIUDPClient的init方法实现如下：

/** * Initializes client object to defaults. * * This enables compression and sets compression threshhold to 15 KB. */ private void init() { this.sanitizeKeys = true; this.primitiveAsString = false; this.compressEnable = true; this.compressThreshold = COMPRESS_THRESH; this.defaultEncoding = "UTF-8"; this.poolName = (this.poolName == null) ? "default" : this.poolName; // get a pool instance to work with for the life of this instance this.pool = SchoonerSockIOPool.getInstance(poolName); }

BinaryClient的init方法实现如下：

/** * Initializes client object to defaults. * * This enables compression and sets compression threshhold to 15 KB. */ private void init() { this.poolName = (this.poolName == null) ? "default" : this.poolName; // get a pool instance to work with for the life of this instance this.pool = SchoonerSockIOPool.getInstance(poolName); }

二：常用方法解析（以AscIIClient实现为例）

首先我们来认识一个方法，定义如下：

/** * Stores data to cache. * * If data does not already exist for this key on the server, or if the key * is being<br/> * deleted, the specified value will not be stored.<br/> * The server will automatically delete the value when the expiration time * has been reached.<br/> * <br/> * If compression is enabled, and the data is longer than the compression * threshold<br/> * the data will be stored in compressed form.<br/> * <br/> * As of the current release, all objects stored will use java * serialization. * * @param cmdname * action to take (set, add, replace, append,prepend, cas) * @param key * key to store cache under * @param value * object to cache * @param expiry * expiration * @param hashCode * if not null, then the int hashcode to use * @return true/false indicating success */ private boolean set(String cmdname, String key, Object value, Date expiry, Integer hashCode, Long casUnique, boolean asString) 该方法的作用就是向服务器端发送指令，从而实现各种功能，截取组装指令的代码段： // construct the command String cmd = new StringBuffer().append(cmdname).append(" ").append(key).append(" ").append(flags).append(" ").append(expiry.getTime() / 1000).append(" ").toString();

由此可见，要明白客户端这些方法在服务器段起到的效果，需要明白服务器段各个指令所达到的效果，这个后面介绍。

方法举例

public boolean add(String key, Object value) { return set("add", key, value, null, null, 0L, primitiveAsString); }

该方法缓存的数据不过期

public boolean add(String key, Object value, Date expiry) { return set("add", key, value, expiry, null, 0L, primitiveAsString); }

该方法指定了数据缓存过期时间（过期时间到将会被自动删除）

其他方式类似，例如set, replace, append,prepend, cas

注意：key、value都不能为null.

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