Session Use Guidelines in Java

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1312 Session Use Guidelines
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Here are some more general guidelines on storing objects in the session:
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They must be objects, serializable by Ruby s Marshal API, which excludes certain
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types of objects such as a database connection and other types of I/O objects
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Large object graphs may exceed the size available for session storage Whether this
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limitation is in effect for you depends on the session store chosen and is covered later in the chapter
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Critical data should not be stored in the session, since it can be suddenly lost by the
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user ending his session (by closing the browser or clearing his or her cookies)
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Objects with attributes that change often should not be kept in the session Modifying the structure of an object and keeping old versions of it stored in the
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session is a recipe for disaster Deployment scripts should clear old sessions to prevent
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133 Storage Mechanisms
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this sort of problem from occurring, but with certain types of session stores, such as the cookie store, this problem is hard to mitigate The simple answer (again) is to just not keep anything except for the occasional id in the session
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132 Session Options
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You used to be able to turn off the session, but as of Rails 3, applications that don t need sessions don t have to worry about them Sessions are lazy-loaded, which means unless you access the session in a controller action, there is no performance implication
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133 Storage Mechanisms
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The mechanism via which sessions are persisted can vary Rails default behavior is to store session data as cookies in the browser, which is fine for almost all applications If you need to exceed the 4KB cookies storage limit inherent in using cookies, then you can opt for an alternative session store But of course, you shouldn t be exceeding that limit, because you shouldn t be keeping much other than an id or two in the session There are also some potential security concerns around session-replay attacks involving cookies, which might push you in the direction of using an alternative session storage
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1331 Active Record Session Store
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The tools to switch over to storing sessions in the database are already built into Rails The first step is to create the necessary migration, using a rake task provided for that very purpose, and run the migration to create the new table:
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$ rake db:sessions:create invoke active_record create db/migrate/20100114005900_add_sessions_tablerb $ rake db:migrate == AddSessionsTable: migrating =============================================== -- create_table(:sessions) -> 00823s -- add_index(:sessions, :session_id) -> 00301s -- add_index(:sessions, :updated_at) -> 00280s == AddSessionsTable: migrated (01433s) ======================================
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Session
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13: Session Management
The second (and final) step is to tell Rails to use the new sessions table to store sessions, via a setting in config/initializers/session_storerb:
MyApplication::Applicationconfigsession_store :active_record_store
That s all there is to it
1332 Memcache Session Storage
If you are running an extremely high-traffic Rails deployment, you re probably already leveraging memcache in some way or another memcache is a remote-process memory cache that helps power some of the most highly trafficked sites on the Internet The memcache session storage option lets you use your memcache server as the repository for session data, and it is blazing fast It s also nice because it has built-in expiration, meaning you don t have to expire old sessions yourself To use memcache, the first step is to modify Rails default session settings in config/initializers/session_storerb At minimum, replace the contents of the file with the following:
MyApplication::Applicationconfigsession_store :mem_cache_store
Note
The Ruby-based memcache client gem, located at http://rubygemsorg/gems/ memcache-client is supposed to ship with Rails If your server startup crashes and complains that it can t find the memcache file to load, manually add memcache_client to your Gemfile If you re feeling particularly geeky, you may try installing one of the memcache clients with native bindings, such as http://githubcom/ninjudd/memcache or http://blogevanweavercom/files/doc/fauna/memcached
The session_store method support options as well
memcache_options = { :c_threshold => 10_000, :compression => true, :debug => false, :namespace => ":app-#{Railsenv}", :readonly => false, :urlencode => false } MyApplication::Applicationconfigsession_store :mem_cache_store, memcache_options
133 Storage Mechanisms
1333 The Controversial CookieStore
In February 2007, core-team member Jeremy Kemper made a pretty bold commit to Rails He changed the default session storage mechanism from the venerable PStore to a new system based on a CookieStore His commit message summed it up well:
Introduce a cookie-based session store as the Rails default Sessions typically contain at most a user id and flash message; both fit within the 4K cookie size limit A secure hash is included with the cookie to ensure data integrity (a user cannot alter his user id without knowing the secret key included in the hash) If you have more than 4K of session data or don t want your data to be visible to the user, pick another session store Cookie-based sessions are dramatically faster than the alternatives
I describe the CookieStore as controversial because of the fallout over making it the default session storage mechanism For one, it imposes a very strict size limit, only 4K A significant size constraint like that is fine if you re following the Rails way, and not storing anything other than integers and short strings in the session If you re bucking the guidelines, well, you might have an issue with it
OpenSSL Digests Lots of people have complained about the inherent insecurity of storing session information, including the current user information on the user s browser However, there are security measures in place that make the cookie store hard to crack open and exploit For instance, you d need to be able to compromise SHA1, which is somewhat difficult to do But let s say you want different security,2 you can easily override the existing hashing code by setting it to any other digest provided by OpenSSL: