In the field of

software development Software development is the process of conceiving, specifying, designing, programming, documenting, testing, and bug fixing involved in creating and maintaining applications, frameworks, or other software components. Software development inv ...

, an interceptor pattern is a

software design pattern In software engineering, a software design pattern is a general, reusable solution to a commonly occurring problem within a given context in software design. It is not a finished design that can be transformed directly into source or machine c ...

that is used when software systems or frameworks want to offer a way to change, or augment, their usual processing cycle. For example, a (simplified) typical processing sequence for a web-server is to receive a URI from the browser, map it to a file on disk, open the file and send its contents to the browser. Any of these steps could be replaced or changed, e.g. by replacing the way URIs are mapped to filenames, or by inserting a new step which processes the files contents. Key aspects of the pattern are that the change is ''transparent'' and used ''automatically''. In essence, the rest of the system does not have to know something has been added or changed and can keep working as before. To facilitate this, a ''predefined interface'' for extension has to be implemented, some kind of ''dispatching'' mechanism is required where interceptors are registered (this may be dynamic, at runtime, or static, e.g. through configuration files) and ''context objects'' are provided, which allow access to the framework's internal state.

Uses & Context

Typical users of this pattern are web-serversApache Software Foundation: Tomcat 6.0 Channel Interceptor Reference, accessed 2009-Nov-24
/ref> (as mentioned above), object-OMG, "CORBA v3.1, Part I: Interfaces", Chapter 16 "Portable Interceptors", January 2008
/ref> and message-oriented middleware An example of implementation of this pattern is the ''javax.servlet.Filter'' interface, which is part of Java Platform, Enterprise Edition.

Aspect-oriented programming In computing, aspect-oriented programming (AOP) is a programming paradigm that aims to increase modularity by allowing the separation of cross-cutting concerns. It does so by adding behavior to existing code (an advice) ''without'' modifying ...

(AOP) can also be used in some situations to provide the capability of an interceptor, although AOP doesn't use the elements typically defined for the interceptor pattern.

References

{{DEFAULTSORT:Interceptor Pattern Architectural pattern (computer science) Concurrent computing Software design patterns