php中__sleep和__wakeup
  在php中，__sleep和___wakeup是两个分别自对象序列化前和后分别调用的方法，
其中__sleep在一个对象序列化前调用，它不接收任何参数，但会返回数组，这里可以放置哪些属性需要序列化，比如下面的例子：

class Customer {
 private $name;
 private $credit_card_number; 
 
public function setName($name) {
 $this->name = $name;
 }
 
public function getName() {
 return $this->name;
 }
 
public function setCC($cc) {
 $this->credit_card_number = $cc;
 }
 
public function getCC() {
 return $this->credit_card_number;
 }
 
public function __sleep() {
 return array(“name”); //只有name会序列化 }
 
}
 
$c = new Customer();
 $c->setName(“Stuard”);
 $c->setCC(“456789″);
 
$data = serialize($c).”\n”;
 echo $data.”\n”;
 
Output:
 O:8:”Customer”:1:{s:14:” Customer name”;s:5:”Stuard”;}

   上面在序列化前，__sleep中指定了只有name属性会序列化，而creaditcard不会。

    而__wakeup则相反，它是在反序列化前触发的，比如下面例子：

class Customer {
 private $name;
 private $credit_card_number; 
 
public function setName($name) {
 $this->name = $name;
 }
 
public function getName() {
 return $this->name;
 }
 
public function setCC($cc) {
 $this->credit_card_number = $cc;
 }
 
public function getCC() {
 return $this->credit_card_number;
 }
 
public function __sleep() {
 return array(“name”);
 }
 
public function __wakeup() {
 if($this->name == “Stuart”) {
  //重新在数据库中获得 
 $this->credit_card_number = “1234567890123456″;
 }
 }
 }
 
$c = new Customer();
 $c->setName(“Stuart”);
 $c->setCC(“1234567890123456″);
 
$data = serialize($c).”\n”;
 var_dump(unserialize($data));
 
Output:
 object(Customer)#2 (2) {
 ["?name:private"?]=>
 string(5) “Stuart”?
 ["?credit_card_number:private"]=>
 string(16) ’12345678901234563
 }

   上面的代码中，因为序列化时使用了__sleep,沒把creadit cardnumber属性序列化，因此在反序列化unserialize调用前，会先调用__wakeup方法，比如这里可以重新在数据库中取得数据，再此进行操作