Cachespec.xml file

The cache parses the cachespec.xml file when the server starts, and extracts a set of configuration parameters from each <cache-entry> element. Every time a new servlet or other cacheable object initializes, the cache attempts to match each of the <cache-entry> elements to find the configuration information for that object. The <cache-entry> elements can be inside the root <cache> element or inside a <cache-instance> element. Cache entries that are in the <root> element are cached with the default cache instance. Cache entries that are in the <cache-instance> element are cached in that particular cache instance. Different cacheable objects have different <class> elements. We can define the specific object a cache policy refers to using the <name> element.

 

Location

Place the cachespec.xml file with the deployment module. Use an assembly tool to define the cacheable objects. See Assembling applications for more information about assembling applications. We can also place a global cachespec.xml file in the application server properties directory.

The cachespec.dtd file is available in the application server properties directory. The cachespec.dtd file defines the legal structure and the elements that can be in your cachespec.xml file.

 

Usage notes

Cachespec.xml elements

The root element of the cachespec.xml file is <cache> and contains <cache-instance> and <cache-entry> elements. The <cache-entry> elements can also be placed inside of <cache-instance> elements to make that cache entry a part of a cache instance that is other than the default.

cache-instance

<cache-instance name="cache_instance_name"></cache-instance>

The name attribute is the Java Naming and Directory Interface (JNDI) name of the cache instance that is set in the administrative console.

Each <cache-instance> element must contain at least one <cache-entry> element. A cache entry that is matched within a <cache-instance> element is cached in the servlet cache instance that is specified by the name attribute. If identical <cache-entry> elements exist across <cache-instance> elements then the first <cache-entry> element that is matched is used.

cache-entry

Each cache entry must specify certain basic information that the dynamic cache uses to process that entry. This section explains the function of each cache entry element of the cachespec.xml file including:

• class

• name

• sharing-policy

• property

• cache-id

With the current version of WebSphere Application Server, you can define multiple cache policies for a single servlet. For example, if you define multiple mappings for a servlet in the web.xml file, one can create a cache entry for each one of the mappings.

class

<class>command | servlet | webservice | JAXRPCClient | static</class>

This element is required and specifies how the application server interprets the remaining cache policy definition. The value servlet refers to servlets and JavaServer Pages (JSP) files that are deployed in the WAS servlet engine. The webservice class extends the servlet with special component types for Web services requests. The JAXRPCClient is used to define a cache entry for the Web services client cache. The value command refers to classes using the WebSphere command programming model. The value static refers to files that contain static content. The following examples illustrate the class element:

<class>command</class>
<class>servlet</class>
<class>webservice</class>
<class>JAXRPCClient</class>
<class>static</class>

name

<name>name</name>

Use the following guidelines for the name element to specify a cacheable object:

• For commands, this required element must include the package name, if any, and class name, including a trailing .class, of the configured object.

• For servlets and JSP files, if the cachespec.xml file is in the WAS properties directory, this required element must include the full URI of the JSP file or servlet to cache. For servlets and JSP files, if the cachespec.xml file is in the Web application, this required element can be relative to the specific Web application context root.

• For Web services, include the Universal Resource Identifier (URI) of the SOAP router associated with the Web service that you want to cache.

• For Web services client cache, the name is the target end point of the cacheable Web service or the URI of the SOAP router that is associated with the cacheable Web service. Use the SOAP address location in the WSDL file to define the name for the Web services client cache.

• For static files, if the cachespec.xml file is in the WAS properties directory, this required element must include the full URI of the file to cache. If the cachespec.xml file is in the Web application, this required element can be relative to the specific Web application context root. For a Web application with a context root, the cache policy for files using the static class must be specified in the Web application, and not in the properties directory.

Note: The preferred location of the cachespec.xml file is in the Web application, not the properties directory.

We can specify multiple <name> elements within a <cache-entry> if you have different mappings that refer to the same servlet.

The following examples illustrate the name element

<name>com.mycompany.MyCommand.class</name>
<name>default_host:/servlet/snoop</name>
<name>com.mycompany.beans.MyJavaBean</name>  
<name>mywebapp/myjsp.jsp</name>
<name>/soap/servlet/soaprouter</name>
<name>http://remotecompany.com:9080/service/getquote</name>
<name>mywebapp/myLogo.gif</name>

sharing-policy

<sharing-policy> not-shared | shared-push | shared-pull | shared-push-pull</sharing-policy>

When working within a cluster with a distributed cache, these values determine the sharing characteristics of entries created from this object. If this element is not present, a not-shared value is assumed. In single server environments, not-shared is the only valid value. When enabling replication, the default value is not-shared . This property does not affect distribution to Edge Side Include processors through the Edge fragment caching property. See Configuring cache replication for more information.

Value	Description
not-shared	Cache entries for this object are not shared among different application servers. These entries can contain non-serializable data. For example, a cached servlet can place non-serializable objects into the request attributes, if the <class> type supports it.
shared-push	Cache entries for this object are automatically distributed to the dynamic caches in other application servers or cooperating JVMs. Each cache has a copy of the entry at the time it is created. These entries cannot store non-serializable data.
shared-pull	Cache entries for this object are shared between application servers on demand. If an application server gets a cache miss for this object, it queries the cooperating application servers to see if they have the object. If no application server has a cached copy of the object, the original application server runs the request and generates the object. These entries cannot store non-serializable data. This mode of sharing is not recommended.
shared-push-pull	Cache entries for this object are shared between application servers on demand. When an application server generates a cache entry, it broadcasts the cache ID of the created entry to all cooperating application servers. Each server then knows whether an entry exists for any given cache ID. On a given request for that entry, the application server knows whether to generate the entry or pull it from somewhere else. These entries cannot store non-serializable data.

The following example shows a sharing policy

<sharing-policy>not-shared</sharing-policy>

property

<property name="key">value</property>

where key is the name of the property for this cache entry element, and value is the corresponding value.

We can set optional properties on a cacheable object, such as a description of the configured servlet. The class determines valid properties of the cache entry. At this time, the following properties are defined:

Property	Valid classes	Value
ApplicationName	All	Overrides the J2EEName application ID so that multiple applications can share a common cache ID namespace.
EdgeCacheable	Servlet	True or false. Default is false. If the property is true, then the given servlet or JSP file is externally requested from an Edge Side Include processor. Whether or not the servlet or JSP file is cacheable depends on the rest of the cache specification.
ExternalCache	Servlet	external cache name. The external cache name needs to match the external cache group name.
consume-subfragments	Servlet or Web service	True or false. Default is false. When a servlet is cached, only the content of that servlet is stored, and includes placeholders for any other fragments to which it includes or forwards. Consume-subfragments (CSF) tells the cache not to stop saving content when it includes a child servlet. The parent entry, the one marked CSF, includes all the content from all fragments in its cache entry, resulting in one big cache entry that has no includes or forwards, but the content from the whole tree of entries. This can save a significant amount of application server processing, but is typically only useful when the external HTTP request contains all the information needed to determine the entire tree of included fragments.
do-not-consume	Servlet or Web service	True or false. Default is false. When a fragment parent has the consume-subfragment property set to true the child fragment content is saved in the cache entry of the parent. Do-not-consume (DNC) tells the cache to stop saving the content for this fragment in the parent cache-entry and create a placeholder instead for the include or forward.
alternate_url	Servlet	alternate URL used to invoke the servlet or JSP file. The property is valid only if the EdgeCacheable property also is set for the cache entry.
persist-to-disk	All	True or false. Default is true. When this property is set to false, the cache entry is not written to the disk when overflow or server stopping occurs.
save-attributes	Servlet	True or false. Default is true. When this property is set to false, the request attributes are not saved with the cache entry. Use the <exclude> element to specify the request attributes that do not apply to the save-attributes property. For example, to save only the attr1 attribute with the cache entry <property name="save-attributes">false <exclude>attr1</exclude> </property> To save all attributes except the attr1 attribute in the cache entry, set the property to true in the preceding sample. If you do not use the <exclude> element, either all or no request attributes are saved with the cache entry.
delay-invalidations	command	True or false. When this property is set to true, the commands that are invalidating cached objects based on the invalidation rules in this cache entry invalidate the cache entries after running. By default, the invalidation occurs before the command runs.

cache-id

To cache an object, the application server must know how to generate a unique ID for different invocations of that object. These IDs are built either from user-written custom Java code or from rules defined in the cache policy of each cache entry. Each cache entry can have multiple cache ID rules that are executed in order until either:

• A rule returns a non-empty cache ID, or

• No more rules are left to execute.

If none of the cache ID generation rules produce a valid cache ID, the object is not cached.

Each cache-id element defines a rule for caching an object and is composed of the sub-elements component, timeout, inactivity, priority, property, idgenerator, and metadatagenerator. The following example illustrates a cache-id

<cache-id>component*| timeout? | inactivity? | priority? | property* | idgenerator? | metadatagenerator?</cache-id>

component sub-element

Use the component sub-element to generate a portion of the cache ID. The component sub-element consists of the attributes id, type, and ignore-value, and the elements index,method, field, required, value, and not-value.

• Use the id attribute to identify the component.

• Use the type attribute to identify the type of component. The following table lists the values for the type.

  Type	Valid classes	Meaning
  method	command	Calls the indicated method on the command or object
  field	command	Retrieves the named field in the command or object
  parameter	servlet	Retrieves the named parameter value from the request object
  parameter-list	servlet	Retrieves a list of values for the named parameter
  session	servlet	Retrieves the named value from the HTTP Session
  cookie	servlet	Retrieves the named cookie value
  attribute	servlet	Retrieves the named request attribute
  header	servlet and Web service	Retrieves the named request header
  pathInfo	servlet	Retrieves the pathInfo from the request
  servletpath	servlet	Retrieves the servlet path
  locale	servlet	Retrieves the request locale
  requestType	servlet	Retrieves the HTTP request method from the request.
  tiles_attribute	servlet	Retrieves the value of an attribute from a tile.
  SOAPEnvelope	Web service and Web services client cache	Retrieves the SOAPEnvelope from a Web services request. An ID attribute of Hash uses a Hash of the SOAPEnvelope, while Literal uses the SOAPEnvelope as received.
  SOAPAction	Web service	Retrieves the SOAPAction header, (if available), for a Web services request.
  serviceOperation	Web service	Retrieves the service operation for a Web services request
  serviceOperationParameter	Web service	Retrieves the specified parameter from a Web services request
  operation	Web services client cache	An operation type in the Web Services Description Language (WSDL) file. The id attribute is ignored and the value is the operation or method name. If the namespace of the operation is specified, the value should be formatted as namespaceOfOperation:nameOfOperation
  part	Web services client cache	An input message part of in the WSDL file or a request parameter. Its id attribute is the part or parameter name, and the value is the part or parameter value.
  SOAPHeaderEntry	Web services client cache	Retrieves special information in the Simple Object Access Protocol (SOAP) header of the Web services request. The id attribute specifies the name of the entry. In addition, the entry of the SOAP header in the SOAP request must have the "actor" attribute which contains com.ibm.websphere.cache. For example <soapenv:Header> <getQuote soapenv:actor="com.ibm.websphere.cache">IBM</getQuote> </soapenv:Header>

• Use the ignore-value attribute to specify whether or not to use the value returned by this component in cache ID formation. This is an optional attribute with a default value of false. If the value is true, only the ID of the component is used when creating a cache ID, or no output is used when creating a dependency or invalidation ID.

• Use the method element to call a void method on a returned object. We can infinitely nest method and field objects in any combination. The method must be public and is not valid for edge-cacheable components. For example

  <component id="getUser" type="method"><method>getUserInfo
  <method>getName</method></method></component>
  

  This method is equivalent to getUser().getUserInfo().getName()

  For component types attribute, method or field that can return an object, when the object returned is a collection or array, the ID is created with a comma separated list of the elements in the collection or array. For example, if the request attribute "users" returns an array [a, b] and the cache entry is defined like the following example

  <cache-entry>
    <class>servlet</class>
    <name>xxx.jsp</name>
    <cache-id>
      .
      .
      <component id="users" type="attribute">
        <required>true</required>
      </component>
      .
      .
    </cache-id>
    <dependency-id>dep
      <component id="users" type="attribute">
        <required>true</required>
      </component>
    </dependency-id>
  </cache-entry>
  

  The cache id contains the string users: a,b. The dependency id is dep: a,b.

  Use the multipleIDs attribute with the component types to specify that multiple dependency IDs (or invalidation IDs) should be generated based on the items in the collection or array. For example

  <cache-entry>
    <class>servlet</class>
    <name>xxx.jsp</name>
    <cache-id>
      .
      .
        <component id="users" type="attribute">
          <required>true</required>
        </component>
      .
      .
    </cache-id>
    <dependency-id>dep
      <component id="users" type="attribute" multipleIDs="true">
        <required>true</required>
      </component>
    </dependency-id>
  </cache-entry>
  

  The cache policy will generates the following dependency IDs:

  • dep:a,b

  • dep:a

  • dep:b

  Use the index element with the above component type to add only the value of the element at the specified index position in the collection or array, to the ID that is being created

  <cache-entry>
    <class>servlet</class>
    <name>xxx.jsp</name>
    <cache-id>
      .
      .
        <component id="users" type="attribute">
          <required>true</required>
          <index>1</index>
        </component>
      .
      .
    </cache-id>
    <dependency-id>dep
      <component id="users" type="attribute" multipleIDs="true">
        <required>true</required>
      </component>
    </dependency-id>
  </cache-entry>
  

  The above cache policy generates the following component to be used in the cache ID: users: b. Use the <method> element to call a void method on a returned object.

• Use the field element to access a field in a returned object. You can infinitely nest method and field objects in any combination. The field must be public. Not valid for edge-cacheable components. For example

  <component id="getUser" type="method"><method>getUserInfo
  <field>name</field></method></component>
  

  This method is equivalent to getUser().getUserInfo().name

• Use the required element to specify whether or not this component must return a non-null value for this cache ID for it to represent a valid cache. If set to true, this component must return a non-null value for this cache ID to represent a valid cache ID. If set to false, the default, a non-null value is used in the formation of the cache ID and a null value means that this component is not used at all in the ID formation. For example

  <required>true</required>
  

• Use the value element to specify values that must match to use this component in cache ID formation. For example

  <component id="getUser" type="method"><value>blue</value> 
  <value>red</value> </component>
  

• Use the not-value element to specify values that must not match to use this component in cache ID formation. This method is similar to <value>, but instead prescribes the defined values from caching. Use multiple <not-value> elements when there is more than one invalid value. For example

  <component id="getUser" type="method">
  <required>true</required>
  <not-value>blue</not-value>
  <not-value>red</not-value></component>
  

The component sub-element can have either a method and a field element, a value element, or a not-value element. The method and field elements apply only to commands. The following example illustrates the attributes of a component sub-element

<component id="isValid" type="method" ignore-value="true"><component>

timeout sub-element

The timeout sub-element is used to specify an absolute time-to-live (TTL) value for the cache entry. For example,

<timeout>value</timeout>

<priority>value</priority>

<property name="key">value</property>