Use this task to define cacheable objects inside the cachespec.xml,
found inside the Web module WEB-INF or enterprise bean META-INF directory.
Before you begin
Enable the dynamic cache. Refer to the Using the dynamic
cache service article for more information.
About this task
You can save a global cachespec.xml in the
application server properties directory, but the recommended method
is to place the cache configuration file with the deployment module.
The root element of the cachespec.xml file is <cache>,
which contains <cache-entry> elements.
Avoid trouble: In situations where there is a global
cachespec.xml file
in the application server properties directory, and a
cachespec.xml file
in an application, the entries in the two cachespec.xml files are
merged. If there are conflicting entries in the two files, the entries
in the in the
cachespec.xml file that is in the application
override the entries in the global
cachespec.xml file for
that application.
gotcha
The <cache-entry> element can be
nested within the <cache> element or a <cache-instance>
element. The <cache-entry> elements that are nested within the <cache>
element are cached in the default cache instance. Any <cache-entry>
elements that are in the <cache-instance> element are cached
in the instance that is specified in the name attribute on
the <cache-instance> element.
Within a <cache-entry>
element are parameters that allow you to complete the following tasks
to enable the dynamic cache with the cachespec.xml file:
Procedure
- Develop a cachespec.xml file.
- Create a caching configuration file.
In
the <app_server_root>/properties directory,
locate the cachespec.sample.xml file.
- Copy the cachespec.sample.xml file to cachespec.xml in
Web module WEB-INF or enterprise bean META-INF directory.
- Define the cache-entry elements necessary to identify the
cacheable objects. See the cachespec.xml file topic for a list of
elements.
- Develop cache ID rules.
To cache an object, WebSphere® Application Server must know
how to generate unique IDs for different invocations of that object.
The <cache-id> element performs that task. Each cache
entry can have multiple cache-ID rules that run in order until either
a rule returns cache-ID that is not empty or no more rules remain
to run. If no cache-ID generation rules produce a valid cache ID,
then the object is not cached. Develop the cache IDs in one of two
ways:
- Use the <component> element defined in the cache
policy of a cache entry (recommended). Refer to the cachespec_xml
file topic for more information about the <component> element.
- Write custom Java code
to build the ID from input variables and system state. To configure
the cache entry to use the ID generator, specify your IdGenerator
in the XML file by using the <idgenerator> tag, for example:
<cache-entry>
<class>servlet</class>
<name>/servlet/CommandProcessor</name>
<cache-id>
<idgenerator>com.mycompany.SampleIdGeneratorImpl</idgenerator>
<timeout>60</timeout>
</cache-id>
</cache-entry>
- Specify dependency ID rules. Use dependency
ID elements to specify additional cache group identifiers that associate
multiple cache entries to the same group identifier.
The dependency
ID is generated by concatenating the dependency ID base string with
the values returned by its component elements. If a required component
returns a null value, then the entire dependency ID does not generate
and is not used. You can validate the dependency IDs explicitly through
the dynamic cache API, or use another cache-entry <invalidation> element.
Multiple dependency ID rules can exist per cache entry. All dependency
ID rules run separately. See the cachespec.xml file topic for a list
of <component> elements.
- Invalidate other cache entries as a side effect of this
object start, if relevant. You can define invalidation
rules in exactly the same manner as dependency IDs. However, the IDs
that are generated by invalidation rules are used to invalidate cache
entries that have those same dependency IDs.
The invalidation
ID is generated by concatenating the invalidation ID base string with
the values returned by its component element. If a required component
returns a null value, then the entire invalidation ID is not generated
and no invalidation occurs. Multiple invalidation rules can exist
per cache-entry. All invalidation rules run separately.
- Ensure your cache policy is working correctly. You
can modify the policies within the cachespec.xml file while
your application is running. The dynamic cache reloads the updated
file automatically. If you are caching static content and you are
adding the cache policy to an application for the first time, you
must restart the application. You do not need to restart the application
server to activate the new cache policy. Refer to the Verifying the
cacheable page topic for more information.
What to do next
Typically you declare several
<cache-entry> elements
inside a
cachespec.xml file.
When new versions of the cachespec.xml are
detected, the old policies are replaced. Objects that cached through
the old policy file are not automatically invalidated from the cache;
they are either reused with the new policy or eliminated from the
cache through its replacement algorithm.
For each of the three
IDs (cache, dependency, invalidation) generated by cache entries,
a <cache-entry> can contain multiple elements. The dynamic
cache runs the <cache-id> rules in order, and the first
one that successfully generates an ID is used to cache that output.
If the object is to be cached, each one of the <dependency-id> elements
is run to build a set of dependency IDs for that cache entry. Finally,
each of the <invalidation> elements are run, building
a list of IDs that the dynamic cache invalidates, whether or not this
object is cached.