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Apache Struts 2 Documentation
Parameter Filter Interceptor
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The Parameter Filter Interceptor blocks parameters from getting to the rest of the stack or your action. You can use multiple parameter filter interceptors for a given action, so, for example, you could use one in your default stack that filtered parameters you wanted blocked from every action and those you wanted blocked from an individual action you could add an additional interceptor for each action.

## Parameters

- allowed - a comma delimited list of parameter prefixes that are allowed to pass to the action
- blocked - a comma delimited list of parameter prefixes that are not allowed to pass to the action
- defaultBlock - boolean (default to false) whether by default a given parameter is blocked. If true, then a parameter must have a prefix in the allowed list in order to be able to pass to the action

The way parameters are filtered for the least configuration is that if a string is in the allowed or blocked lists, then any parameter that is a member of the object represented by the parameter is allowed or blocked respectively.

For example, if the parameters are:

- blocked: person,person.address.createDate,personDao
- allowed: person.address
- defaultBlock: false

The parameters person.name, person.phoneNum etc would be blocked because 'person' is in the blocked list. However, person.address.street and person.address.city would be allowed because person.address is in the allowed list (the longer string determines permissions).

## Example

    <interceptors>
        ...
        <interceptor name="parameterFilter" class="com.opensymphony.xwork2.interceptor.ParameterFilterInterceptor"/>
        ...
    </interceptors>

    <action ....>
         ...
         <interceptor-ref name="parameterFilter">
              <param name="blocked">person,person.address.createDate,personDao</param>
         </interceptor-ref>
         ...
    </action>