Interceptor pattern
Encyclopedia
In the field of software development
, an interceptor pattern is a software design pattern
that is used when software systems or framework
s 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, i.e. 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 systems 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 frameworks internal state.
An example of implementation of this pattern is the javax.servlet.Filter interface, which is part of Java Platform, Enterprise Edition
.
Aspect-Oriented Programming (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.
Software development
Software development is the development of a software product...
, an interceptor pattern is a software design pattern
Design pattern
A design pattern in architecture and computer science is a formal way of documenting a solution to a design problem in a particular field of expertise. The idea was introduced by the architect Christopher Alexander in the field of architecture and has been adapted for various other disciplines,...
that is used when software systems or framework
Software framework
In computer programming, a software framework is an abstraction in which software providing generic functionality can be selectively changed by user code, thus providing application specific software...
s 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, i.e. 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 systems 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 frameworks internal state.
Uses & Context
Typical users of this pattern are web-servers (as mentioned above), object- and message-oriented middlewareAn example of implementation of this pattern is the javax.servlet.Filter interface, which is part of Java Platform, Enterprise Edition
Java Platform, Enterprise Edition
Java Platform, Enterprise Edition or Java EE is widely used platform for server programming in the Java programming language. The Java platform differs from the Java Standard Edition Platform in that it adds libraries which provide functionality to deploy fault-tolerant, distributed, multi-tier...
.
Aspect-Oriented Programming (AOP)
Aspect-oriented programming
In computing, aspect-oriented programming is a programming paradigm which aims to increase modularity by allowing the separation of cross-cutting concerns...
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.