4.3. Zend_Cache前端

Zend_Cache_Core是一个特别的前端,因为他是模块的核心. 它是一个一般化(generic)的缓存前端,并且由其他类扩展.

	注意
	所有的前端继承自Zend_Cache_Core因此它的方法和选项(描述如下)应该在其他的前端中可用,所以这里没有进行文档化.

这些选项被传递给如前面例子中演示的工厂方法.

An example is given in the manual at the very beginning.

如果你只向缓存中存储字符串(由于"automatic_serialization"选项,可能会存储一些布尔值),你可以使用更加简介的构造:

// 假定你已经有 $cache

$id = 'myBigLoop'; // cache id of "what we want to cache"

if (!($data = $cache->load($id))) {
    // cache miss

    $data = '';
    for ($i = 0; $i < 10000; $i++) {
        $data = $data . $i;
    }

    $cache->save($data);

}

// [...] do something with $data (echo it, pass it on etc.)

            

如果你缓存多个块或则数据实例,意思是一样的:

// 确保使用独一无二的 identifiers:
$id1 = 'foo';
$id2 = 'bar';

// block 1
if (!($data = $cache->load($id1))) {
    // cache missed

    $data = '';
    for ($i=0;$i<10000;$i++) {
        $data = $data . $i;
    }

    $cache->save($data);

}
echo($data);

// this isn't affected by caching
echo('NEVER CACHED! ');

// block 2
if (!($data = $cache->load($id2))) {
    // cache missed

    $data = '';
    for ($i=0;$i<10000;$i++) {
        $data = $data . '!';
    }

    $cache->save($data);

}
echo($data);

            

如果你想缓存特殊值（带 "automatic_serialization" 选项的布尔值）或不能用上述紧缩结构的空字符串，你需要正式地测试缓存记录。

// the compact construction 
// (not good if you cache empty strings and/or booleans)
if (!($data = $cache->load($id))) {

    // cache missed

    // [...] we make $data

    $cache->save($data);

}

// we do something with $data

// [...]

// the complete construction (works in any case)
if (!($cache->test($id))) {

    // cache missed

    // [...] we make $data

    $cache->save($data);

} else {

    // cache hit

    $data = $cache->load($id);

}

// we do something with $data

            

Zend_Cache_Frontend_Output 是一个输出捕捉前端.它在PHP中使用输出缓冲捕获start() 和 end() 方法间的一切输出.

该前端除了Zend_Cache_Core那些选项外没有任何特定的选项.

An example is given in the manual at the very beginning. Here it is with minor changes:

// if it is a cache miss, output buffering is triggered
if (!($cache->start('mypage'))) {

    // output everything as usual
    echo 'Hello world! ';
    echo 'This is cached ('.time().') ';

    $cache->end(); // output buffering ends

}

echo 'This is never cached ('.time().').';

            

Using this form it is fairly easy to set up output caching in your already working project with little or no code refactoring.

Zend_Cache_Frontend_Function caches the results of function calls. It has a single main method named call() which takes a function name and parameters for the call in an array.

在PHP中使用 call() 函数于使用 call_user_func_array()相同:

$cache->call('veryExpensiveFunc', $params);

// $params is an array 
// For example to call veryExpensiveFunc(1, 'foo', 'bar') with 
// caching, you can use 
// $cache->call('veryExpensiveFunc', array(1, 'foo', 'bar'))

            

Zend_Cache_Frontend_Function is smart enough to cache both the return value of the function and its internal output.

	注意
	You can pass any built in or user defined function with the exception of array(), echo(), empty(), eval(), exit(), isset(), list(), print() and unset().

Zend_Cache_Frontend_Class is different from Zend_Cache_Frontend_Function because it allows caching of object and static method calls.

For example, to cache static calls :

class test {

    // Static method
    public static function foobar($param1, $param2) {
        echo "foobar_output($param1, $param2)";
        return "foobar_return($param1, $param2)";
    }

}

// [...]
$frontendOptions = array(
    'cached_entity' => 'Test' // The name of the class
);
// [...]

// The cached call
$result = $cache->foobar('1', '2');

            

To cache classic method calls :

class Test {

    private $_string = 'hello !';

    public function foobar2($param1, $param2) {
        echo($this->_string);
        echo "foobar2_output($param1, $param2)";
        return "foobar2_return($param1, $param2)";
    }

}

// [...]
$frontendOptions = array(
    'cached_entity' => new Test() // An instance of the class
);
// [...]

// The cached call
$result = $cache->foobar2('1', '2');

            

Zend_Cache_Frontend_File is a frontend driven by the modification time of a "master file". It's really interesting for examples in configuration or templates issues.

For instance, you have an XML configuration file which is parsed by a function which returns a "config object" (like with Zend_Config). With Zend_Cache_Frontend_File, you can store the "config object" into cache (to avoid the parsing of the XML config file at each time) but with a sort of strong dependency on the "master file". So, if the XML config file is modified, the cache is immediately invalidated.

Use of this frontend is the same than of Zend_Cache_Core. There is no need of a specific example - the only thing to do is to define the master_file when using the factory.

Zend_Cache_Frontend_Page is like Zend_Cache_Frontend_Output but designed for a complete page. It's impossible to use Zend_Cache_Frontend_Page for caching only a single block.

On the other hand, the "cache id" is calculated automatically with $_SERVER['REQUEST_URI'] and (depending on options) $_GET, $_POST, $_SESSION, $_COOKIE, $_FILES. More over, you have only one method to call (start()) because the end() call is fully automatic when the page is ended.

For the moment, it's not implemented but we plan to add a HTTP conditional system to save bandwidth (the system will send a HTTP 304 Not Modified if the cache is hit and if the browser has already the good version).

Use of Zend_Cache_Frontend_Page is really trivial :

// [...] // require, configuration and factory

$cache->start();
// if the cache is hit, the result is sent to the browser and the script stop here

// rest of the page ...

            

a more complex example which shows a way to get a centralized cache management in a bootstrap file (for using with Zend_Controller for example)

/*
 * you should avoid putting too many lines before the cache section.
 * For example, for optimal performances, "require_once" or 
 * "Zend_Loader::loadClass" should be after the cache section.
 */

$frontendOptions = array(
   'lifetime' => 7200,
   'debug_header' => true, // for debugging
   'regexps' => array(
       // cache the whole IndexController
       '^/$' => array('cache' => true),
       
       // cache the whole IndexController
       '^/index/' => array('cache' => true),
       
       // we don't cache the ArticleController...
       '^/article/' => array('cache' => false),
       
       // ... but we cache the "view" action of this ArticleController
       '^/article/view/' => array(              
           'cache' => true,
           
           // and we cache even there are some variables in $_POST
           'cache_with_post_variables' => true,
           
           // but the cache will be dependent on the $_POST array 
           'make_id_with_post_variables' => true 
       )
   )
);

$backendOptions = array(
    'cache_dir' => '/tmp/'
);

// getting a Zend_Cache_Frontend_Page object
$cache = Zend_Cache::factory('Page', 
                             'File', 
                             $frontendOptions, 
                             $backendOptions);

$cache->start();
// if the cache is hit, the result is sent to the browser and the 
// script stop here

// [...] the end of the bootstrap file 
// these lines won't be executed if the cache is hit

            

因为设计问题，在有些情况下（例如使用非 HTTP/200 返回代码时），你可能需要取消当前缓存处理，所以 我们引入这个特别的前端，cancel()方法。

// [...] // require, configuration and factory

$cache->start();

// [...]

if ($someTest) {
    $cache->cancel();
    // [...]
}

// [...]