Example: Web Utilities Java Package

1
ExampleWeb Utilities Java Package

• Goals of the package
• Provide web utilities to web clients (browsers,
  web-enabled desktops or file managers, ...)
• Encapsulate web concepts (cookies, request
  headers, MIME-types, resources, cache)
• Concerns
• Should everything exist in caller's memory space?
• Should cache be system- or user-wide?
• Could Web Utilities memory be better handled by
  exploiting what we know about its allocation and
  deallocation behavior?

2
Web Utilities
Connection
Mimetype
Request
Response
Web Utilities
URL
Cache
Site
Resource
Cookie
3
What we Want Cache

• Define the behavior we want in order to
  cache-enable the system
• When a new Resource object is created (and
  associated with a Site object and resource path),
  check the cache for a match first
• When a Resource is asked to load() (creating a
  new Request/Response pair), check to see if the
  Response is cached
• When the cache gets too large, purge some of the
  older entries

4
What we Want Memory

• Define the behavior we want in order to use the
  right type of memory
• Cacheable items should be placed in Cache memory
  instead of thread-associated ScopedMemory or
  HeapMemory
• Cache should have a limited maximum size
• This could be enforced with a MemoryArea instance
  of a particular size
• We may not want to use a mark sweep garbage
  collector for Cache memory
• Use our own design of garbage collector, or
• Make Cache memory immortal, handle Cache memory
  manually within Cache object

5
Observations

• These memory and caching concerns crosscut the
  functionality of the package
• Can't easily modularize these concerns they are
  strongly coupled with each other and the rest of
  the package
• Code copy paste
• No clean way in RTJava to put our objects in
  different memory areas than the caller
• May want to handle caching or Cache memory
  differently in different contexts
• Resource prefetching

6
Aspect-Oriented Programming

• Intercept calls to create new Resources and other
  Cacheable objects
• Put them in Cache memory
• Cache object notification
• Respond to the context in which we were called
• Browser vs. automatic webcrawler
• Modularity within the package code itself
• Separated cache and memory concerns