Adobe 38043740 - ColdFusion Standard - Mac Development Manual page 309

DEVELOPING COLDFUSION 9 APPLICATIONS
Developing CFML Applications
About client and session variables
ColdFusion provides two tools for managing the client state: client variables and session variables. Both types of
variables are associated with a specific client, but you manage and use them differently, as described in the following
table:
Variable type Description
Client Data is saved as cookies, database entries, or Registry entries. Data is saved between server restarts, but is initially
accessed and saved more slowly than data stored in memory.
Each type of data storage has its own time-out period. You can specify the database and Registry data time-outs
in the ColdFusion Administrator. ColdFusion sets Cookie client variables to expire after approximately ten years.
Data is stored on a per-user and per-application basis. For example, if you store client variables as cookies, the user
has a separate cookie for each ColdFusion application provided by a server.
Client variables must be simple variables, such as numbers, dates, or strings. They cannot be arrays, structures,
query objects, or other objects.
Client variable names can include periods. For example, My.ClientVar is a valid name for a simple client variable.
Avoid such names, however, to ensure code clarity.
You do not have to prefix client variables with the scope name when you reference them, However, if you do not
use the Client prefix, you might unintentionally refer to a variable with the same name in another scope. Using
the prefix also optimizes performance and increases program clarity.
You do not lock code that uses client variables.
You can use client variables that are stored in cookies or a common database in clustered systems.
Session Data is stored in memory so it is accessed quickly.
Data is lost when the client browser is inactive for a time-out period. You specify the time-out in the ColdFusion
Administrator, the Application.cfc initialization code, or Application.cfm.
As with client variables, data is available to a single client and application only.
Variables can store any ColdFusion data type.
You must prefix all variable names with the Session scope name.
Lock code that uses session variables to prevent race conditions.
You can use session variables in clustered systems only if the systems support "sticky" sessions, where a session is
limited to a single server.
Session variables are normally better than client variables for values that need to exist for only a single browser session.
Reserve client variables for client-specific data, such as client preferences that you want available for multiple browser
sessions.
Maintaining client identity
Because the web is a stateless system, client management requires some method for maintaining knowledge of the
client between requests. Normally you do this using cookies, but you can also do it by passing information between
application pages. Information about how ColdFusion maintains client identity in a variety of configurations and
environments, and the issues that can arise with client state management are described as follows:
About client identifiers
To use client and session variables, ColdFusion must be able to identify the client. It normally does so by setting the
following two cookie values on the client's system:
• CFID: A sequential client identifier
• CFToken: A random-number client security token
Last updated 1/20/2012
304