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
* 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.
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