java memcache客户端过期时间设置
使用com.danga.MemCached需要注意set方法，通过查看源码发现一直以来的误区，之前用MemcacheClient时，直接使用:
public boolean set(String key, Object value, Integer hash) {
return set("set",key,value, null, hash);
}
原来int只是hash值而已，真正存到memcache确是永不过期，正确用法是调用：
public boolean set(String key, Object value, Date expiry) {
return set("set",key,value,expiry,null);
}
最后，所有的操作都是调用另外的重载set：
try {
String cmd = cmdname + " " + key + " " + flags + " " +
expiry.getTime() / 1000 + " " + val.length + "\r\n";
sock.out().writeBytes(cmd);
sock.out().write(val);
sock.out().writeBytes("\r\n");
sock.out().flush();
String tmp = sock.in().readLine();
if (tmp.equals("STORED")) {
if (debug) {
System.out.println("MemCache: " + cmdname + " " + key + " = " + val);
}
return true;
} else {
System.out.println("MemCache:" + cmd + tmp);
}
} catch (IOException e) {
sock.close();
}
这里可以看到expiry.getTime() / 1000可就是说expriy的单位是毫秒，但是这个时间是相对时间还是绝对时间，现在从客户单api看不出来了，只能通过看memcache服务端代码：
#define REALTIME_MAXDELTA 60*60*24*30
/*
* given time value that's either unix time or delta from current unix time, return
* unix time. Use the fact that delta can't exceed one month (and real time value can't
* be that low).
*/
static rel_time_t realtime(const time_t exptime) {
/* no. of seconds in 30 days - largest possible delta exptime */
if (exptime == 0) return 0; /* 0 means never expire */
if (exptime > REALTIME_MAXDELTA) {
/* if item expiration is at/before the server started, give it an
expiration time of 1 second after the server started.
(because 0 means don't expire). without this, we'd
underflow and wrap around to some large value way in the
future, effectively making items expiring in the past
really expiring never */
if (exptime <= process_started)
return (rel_time_t)1;
return (rel_time_t)(exptime - process_started);
} else {
return (rel_time_t)(exptime + current_time);
}
}
memcache的最长过期时间是30天，并且相对时间和绝对时间都是可以的。