zend-filter provides a set of commonly needed data filters. It also provides a simple filter chaining mechanism by which multiple filters may be applied to a single datum in a user-defined order.
What is a filter?
In the physical world, a filter is typically used for removing unwanted portions of input, and the desired portion of the input passes through as filter output (e.g., coffee). In such scenarios, a filter is an operator that produces a subset of the input. This type of filtering is useful for web applications: removing illegal input, trimming unnecessary white space, etc.
This basic definition of a filter may be extended to include generalized
transformations upon input. A common transformation applied in web applications
is the escaping of HTML entities. For example, if a form field is automatically
populated with untrusted input (e.g., from a web browser), this value should
either be free of HTML entities or contain only escaped HTML entities, in order
to prevent undesired behavior and security vulnerabilities. To meet this
requirement, HTML entities that appear in the input must either be removed or
escaped. Of course, which approach is more appropriate depends on the situation.
A filter that removes the HTML entities operates within the scope of the first
definition of filter - an operator that produces a subset of the input. A filter
that escapes the HTML entities, however, transforms the input (e.g.,
&). Supporting such use cases for web developers is
important, and “to filter”, in the context of using zend-filter, means to
perform some transformations upon input data.
Basic usage of filters
Having this filter definition established provides the foundation for
Zend\Filter\FilterInterface, which requires a single method named
to be implemented by a filter class.
Following is a basic example of using a filter upon two input data, the
&) and double quote (
$htmlEntities = new Zend\Filter\HtmlEntities(); echo $htmlEntities->filter('&'); // & echo $htmlEntities->filter('"'); // "
Also, if a filter inherits from
Zend\Filter\AbstractFilter (as do all of the
out-of-the-box filters), you can also use them as invokables:
$strtolower = new Zend\Filter\StringToLower; echo $strtolower('I LOVE ZF2!'); // i love zf2! $zf2love = $strtolower('I LOVE ZF2!');
Using the StaticFilter
If it is inconvenient to load a given filter class and create an instance of the
filter, you can use
StaticFilter with its
execute() method as an alternative
invocation style. The first argument of this method is a data input value, that
you would pass to the
filter() method. The second argument is a string, which
corresponds to the basename of the filter class, relative to the
execute() method automatically loads the class, creates an
instance, and applies the
filter() method to the data input.
echo StaticFilter::execute('&', 'HtmlEntities');
You can also pass an array of constructor arguments, if they are needed for the filter class:
echo StaticFilter::execute( '"', 'HtmlEntities', ['quotestyle' => ENT_QUOTES] );
The static usage can be convenient for invoking a filter ad hoc, but if you have
the need to run a filter for multiple inputs, it’s more efficient to follow the
first example above, creating an instance of the filter object and calling its
FilterChain class allows you to instantiate and run multiple filter
and validator classes on demand to process sets of input data. See the
FilterChain chapter for more details.
You can set and receive the
FilterPluginManager for the
amend the standard filter classes.
$pluginManager = StaticFilter::getPluginManager()->setInvokableClass( 'myNewFilter', 'MyCustom\Filter\MyNewFilter' ); StaticFilter::setPluginManager(new MyFilterPluginManager());
This is useful when adding custom filters to be used by the
When using two filters in succession, you have to keep in mind that it is often not possible to get the original output by using the opposite filter. Take the following example:
$original = 'my_original_content'; // Attach a filter $filter = new Zend\Filter\Word\UnderscoreToCamelCase(); $filtered = $filter->filter($original); // Use it's opposite $filter2 = new Zend\Filter\Word\CamelCaseToUnderscore(); $filtered = $filter2->filter($filtered)
The above code example could lead to the impression that you will get the
original output after the second filter has been applied. But thinking logically
this is not the case. After applying the first filter,
be changed to
MyOriginalContent. But after applying the second filter, the result
As you can see it is not always possible to get the original output by using a filter which seems to be the opposite. It depends on the filter and also on the given input.
Providing filters via modules
If you wish to indicate that your zend-mvc module provides filters, have your
Module class implement
Zend\Filter\FilterProviderInterface, which defines
/** * @return array */ public function getFilterConfig();
The method should return an array of configuration following the zend-servicemanager configuration format.
If you are not using zend-mvc, but are using a dependency injection container
(e.g., if you are using Expressive), you can also provide filters using the
filters configuration key; the value of that key should be
zend-servicemanager configuration, as linked above.
(zend-mvc users may also provide configuration in the same way, and omit
implementation of the
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