How to implement cache policy with Java Callout

I understand that

• you have a Java callout that connects to a database and forms a JSON blob as an output.
• you would like to cache this result and use it in later requests
• You have tried using the ResponseCache policy, but it's not working as desired

You cannot use ResponseCache for this purpose.

I advise that you rely on the LookupCache and PopulateCache policies, as well as the AssignMessage policy. The flow logic will look something like this:

<Step>
  <Name>Cache-LookupJsonBlob</Name>
</Step>
<Step>
  <Condition>cached_result = null</Condition>
  <Name>Java-DatabaseLookup</Name>
</Step>
<Step>
  <Condition>cached_result = null</Condition>
  <Name>Cache-PopulateJsonBlob</Name>
</Step>
<Step>
  <Condition>cached_result = null</Condition>
  <Name>Cache-LookupJsonBlob</Name>
</Step>
<Step>
  <Condition>cached_result = null</Condition>
  <Name>RaiseFault-CacheFailure</Name>
</Step>
<Step>
  <Name>AssignMessage-Response</Name>
</Step>

Does this make sense?

The Cache lookup and Java db read can both be parameterized, of course. The output of the Java callout would be to ... set a context variable.

The Cache-populate step takes THAT context variable and places it into cache with the appropriate key.

The AssignMessage policy takes the output of the Cache lookup policy (a different context variable) and places it into the response message.