memcached java client 3.0.2详解

t4r23

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 * deleted, the specified value will not be stored. * The server will automatically delete the value when the expiration time * has been reached. * * If compression is enabled, and the data is longer than the compression * threshold * the data will be stored in compressed form. * * 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.