All Things WebSphere

Caching as a best practice to improve response times and reduce CPU utilization is well-established.
There are two aspects to caching webservices responses in WebSphere Application Server with Dynacache Responses can be cached on the client side or on the server side. To enable webservices caching follow the steps listed below:

1. Enable the dynamic cache service on the web container of the application server from: Application Servers --> Web Container --> Enable servlet caching
2. Provide a cachespec.xml file in the WEB-INF directory of the webservice web project. This will contain the caching information toWebSphere. See below for what this file should contain 
3. Display cache information using the Cache monitor. This can be installed from the WebSphere installableApps directory

The following request options are available for creating a cache policy to cache webservices: Find the full list of supported cache policy parameters in the cachespec.xml here

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>

WebServices Client side caching:
Dynacache runtime has an inbuilt client side JAX-RPC cache handler that intercepts received responses and caches it based on a cache policy specified in the cachespec.xml. You will need to use the JAXRPCClient class in the cachespec.xml to cache server-side webservices responses. Excellent article on client-side webservices caching Sample cachespec.xml and corresponding wsdl file:

<cache>
 <cache-entry>
  <class>JAXRPCClient</class>
  <name>http://TradeSample.com:9080/service/getquote</name>
  <cache-id>
   <component id="hash" type="SOAPEnvelope"/>
   <timeout>60</timeout>
  </cache-id>
 </cache-entry>
</cache>

WebServices server side caching:
Dynacache intercepts a server side webservices response. You will need to use the webservice class in the cachespec.xml to cache server-side webservices responses. Sample cachespec.xml and corresponding wsdl file:

<cache>
<cache-entry>
 <class>webservice</class>
 <name>/services/DataProxy</name>
 <sharing-policy>not-shared</sharing-policy>
 <cache-id>
  <component id="id" type="serviceOperationParameter"/>
  <timeout>3600</timeout>
  <priority>1</priority>
 </cache-id>
</cache-entry>
</cache>

Caching of WebServices responses ONLY works for JAX-RPC style webservices and SOAP1.1 responses. For caching ANY webservices response including  ones based on the JAX-WS , JAX-RPC on SOAP 1.1 or SOAP1.2  you can use custom Java code to build the cache id from input SOAP message content. 

If you use custom Java code to build the cache id, create an ID generator Java class that implements the IdGenerator interface defined in the com.ibm.websphere.cache.webservices.IdGenerator package and add a reference to the class you create in the cachespec.xml file by using the idgenerator tag. You can also optionally  implement the com.ibm.websphere.cache.webservices.MetaDataGenerator package to assign cache metadata such as timeout, priority, and dependency ids to cache entries using the metadatagenerator tag as well as implement the Implement the com.ibm.websphere.cache.webservices.InvalidationGenerator interface and use the invalidationgenerator tag in the cachespec.xml file to generate cache ids and to invalidate entries in the cache. The id generated by the invalidation generator can be a cache id or a dependency id.

src code: Client IdGenerator :
sample idgenerator cachespec.xml for client side webservices response caching:

<cache-entry>
 <class>JAXRPCClient</class>
 <name>http://TradeSample.com:9080/service/getquote</name>
 <cache-id>
  <idgenerator>com.mycompany.SampleIdGeneratorImpl</idgenerator>
  <metadatagenerator>
       com.mycompany.SampleMetaDataAndInvalidationGeneratorImpl
    </metadatagenerator>
  <timeout>60</timeout>
 </cache-id>
 <invalidation>http://TradeSample.com:9080/service/GetQuote
  <invalidationgenerator>
       com.mycompany.SampleMetaDataAndInvalidationGeneratorImpl
    </invalidationgenerator>
 </invalidation>
</cache-entry>

src code on git: webservices IdGenerator for serverside caching
sample idgenerator cachespec.xml for server side webservices response caching:

<cache>
<cache-entry>
        <class>webservice</class>
        <name>/Services/MyService</name>
        <sharing-policy>not-shared</sharing-policy>
        <cache-id>
                <timeout>600</timeout>
                <priority>1</priority>
   <idgenerator>
    com.ibm.my.WS_IdGenerator
   </idgenerator>
        </cache-id>
</cache-entry>
</cache>

This IdGenerator class has to be bundled as a shared library and associated with an application server.  Follow the steps below to add the idgenerator as a shared libarary to your server
1.  Select an application server.
2.  In the Server Infrastructure section, expand the Java and ProcessManagement. Select Class loader.
3.  Choose New, and select a class loader order for this class loader, Classes loaded with parent class loader first or Classes loaded with local class loader first (parent last). Click OK.
4.  Click the class loader that is created.
5.  Click Shared library references.
6.  Click Add, and select the library you want to associate to this application server. Repeat this operation to associate multiple libraries to this class
loader.
7.  Click OK.
8.  Save the configuration.
9.  Restart the application server for the changes to take effect.

Takeaway: WebServices caching can yield performance benefit to the tune of an order of magnitude. 100%, 200% improvement for exteremely heavy responses is not unusual. Leverage the free cache of WebSphere i.e. Dynacache and ALL its tooling CacheMonitor, Extended Cache monitor, PMI statistics and the JMX mbean to cache, administer and manage your webservices responses.