[[_custom_interceptors_chapter]]
== Custom Interceptors
It is possible to add custom interceptors to Infinispan, both declaratively and programatically. Custom interceptors are a way of extending Infinispan by being able to influence or respond to any modifications to cache. Example of such modifications are: elements are added/removed/updated or transactions are committed. For a detailed list refer to link:http://docs.jboss.org/infinispan/{infinispanversion}/apidocs/org/infinispan/interceptors/base/CommandInterceptor.html[CommandInterceptor] API.

=== Adding custom interceptors declaratively
Custom interceptors can be added on a per named cache basis. This is because each named cache have its own interceptor stack. Following xml snippet depicts the ways in which a custom interceptor can be added. 

[source,xml]
----
   <local-cache name="cacheWithCustomInterceptors">
      <!--
      Define custom interceptors.  All custom interceptors need to extend org.jboss.cache.interceptors.base.CommandInterceptor
      -->
      <custom-interceptors>
         <interceptor position="FIRST" class="com.mycompany.CustomInterceptor1">
               <property name="attributeOne">value1</property>
               <property name="attributeTwo">value2</property>
         </interceptor>
         <interceptor position="LAST" class="com.mycompany.CustomInterceptor2"/>
         <interceptor index="3" class="com.mycompany.CustomInterceptor1"/>
         <interceptor before="org.infinispanpan.interceptors.CallInterceptor" class="com.mycompany.CustomInterceptor2"/>
         <interceptor after="org.infinispanpan.interceptors.CallInterceptor" class="com.mycompany.CustomInterceptor1"/>
      </custom-interceptors>
   </local-cache>


----

=== Adding custom interceptors programatically
In order to do that one needs to obtain a reference to the link:http://docs.jboss.org/infinispan/{infinispanversion}/apidocs/org/infinispan/AdvancedCache.html[AdvancedCache] . This can be done ass follows:

[source,java]
----
CacheManager cm = getCacheManager();//magic
Cache aCache = cm.getCache("aName");
AdvancedCache advCache = aCache.getAdvancedCache();

----

Then one of the _addInterceptor()_ methods should be used to add the actual interceptor. For further documentation refer to link:http://docs.jboss.org/infinispan/{infinispanversion}/apidocs/org/infinispan/AdvancedCache.html[AdvancedCache] javadoc.

=== Custom interceptor design
When writing a custom interceptor, you need to abide by the following rules.

*  Custom interceptors must extend link:http://docs.jboss.org/infinispan/{infinispanversion}/apidocs/org/infinispan/interceptors/base/BaseCustomInterceptor.html[BaseCustomInterceptor]

* Custom interceptors must declare a public, empty constructor to enable construction.

* Custom interceptors will have setters for any property defined through property tags used in the XML configuration.

