Context Object

See Core J2EE Patterns, 2nd Edition for full description of this pattern and its strategies.

Problem

You want to avoid using protocol-specific system information outside of its relevant context.

Forces

• You have components and services that need access to system information.
• You want to decouple application components and services from the protocol specifics of system information.
• You want to expose only the relevant APIs within a context.

Solution

Use a Context Object to encapsulate state in a protocol-independent way to be shared throughout your application.

Class Diagram

Sequence Diagram

Strategies

• Request Context Strategies
  • Request Context Map Strategy
  • Request Context POJO Strategy
  • Request Context Validation Strategy
• Configuration Context Strategies
  • JSTL Configuration Strategy
  • Security Context Strategy
• General Context Object Strategies
  • Context Object Factory Strategy
  • Context Object Auto-Population Strategy

Consequences

• Improves reusability and maintainability
• Improves testability
• Reduces constraints on evolution of interfaces
• Reduces performance

Related Patterns

• Intercepting Filter
  An Intercepting Filter can use a ContextFactory to create a Context Object during web request handling.
• Front Controller
  A Front Controller can use a ContextFactory to create a Context Object during web request handling
• Application Controller
  An Application Controller can use a ContextFactory to create a Context Object during web request handling
• Transfer Object
  A Transfer Object is used specifically to transfer state across remote tiers to reduce network communication, while a Context Object is used to hide implementation details, improving reuse and maintainability.

Excerpted from Core J2EE Patterns, 2nd Edition. See the book for full description of the pattern including class diagrams, sequence diagrams and sample code.