Policies are an integral part when writing business logic in Strolch. In many cases it would suffice to write
+ all such logic in Services and Commands, but as soon as behaviour can change,
+ depending on the element being accessed, then this would quickly lead to many if/else blocks.
Since writing large if/else blocks is not maintanable in the long run, Strolch offers a different approach. + All Strolch elements can store Policy definitions. This is a simple key/value store where the key defines + the type of policy, and the value references the policy to use.
+ +Currently there are two ways to reference a policy in Strolch, either via a key which defines a further
+ lookup in the PolicyHandler, or directly as the name of the class to instantiate.
Using policies in Strolch gives the additional possibility of easily changing the behaviour at runtime, as a + Service and/or Command would delegate the behaviour to the currently configured policy on the releveant + element.
+ +Policies are implemented by defining an abstract class and extends StrolchPolicy. This abstract
+ class then defines the API of the actual policy. A concrete class then extends this abstract class and
+ implements the concrete methods.
Policies are registered on Resources, Orders, Activities and Actions. The following shows defining two + policies on a Resource, a PlanningPolicy, an ExecutionPolicy in XML:
++<Resource ...> + ... + <Policies> + <Policy Type="PlanningPolicy" Value="key:SimplePlanning" /> + <Policy Type="ExecutionPolicy" Value="java:li.strolch.policytest.TestSimulatedExecutionPolicy" /> + </Policies> +</Resource>+ +
Note how the PlanningPolicy has a value of key:SimplePlanning and the ExecutionPolicy
+ defines a reference to an actual class.
+
To use the PolicyHandler, it must be configured in the StrolchConfiguration.xml as follows:
++<Component> + <name>PolicyHandler</name> + <api>li.strolch.policy.PolicyHandler</api> + <impl>li.strolch.policy.DefaultPolicyHandler</impl> + <Properties> + <readPolicyFile>true</readPolicyFile> + <policyConfigFile>StrolchPolicies.xml</policyConfigFile> + </Properties> +</Component>+ +
+
And this policy handler implementation requires a file where the lookups for the policies is defined, + e.g.:
++<StrolchPolicies> + + <PolicyType Type="PlanningPolicy" Api="li.strolch.policytest.TestPlanningPolicy"> + <Policy Key="SimplePlanning" Class="li.strolch.policytest.TestSimplePlanningPolicy" /> + </PolicyType> + + <PolicyType Type="ConfirmationPolicy" Api="li.strolch.policytest.TestConfirmationPolicy"> + <Policy Key="NoConfirmation" Class="li.strolch.policytest.TestNoConfirmationPolicy" /> + </PolicyType> + +</StrolchPolicies>+ +
+
Now at runtime we can access the policies:
+
+PolicyHandler policyHandler = getComponent(PolicyHandler.class);
+
+try (StrolchTransaction tx = openTx()) {
+
+ Resource res = tx.getResourceBy("TestType", "MyTestResource");
+ PolicyDefs policyDefs = res.getPolicyDefs();
+
+ PolicyDef planningPolicyDef = policyDefs.getPolicyDef("PlanningPolicy");
+ PlanningPolicy planningPolicy = policyHandler.getPolicy(planningPolicyDef, tx);
+ planningPolicy.plan(...);
+
+ PolicyDef executionPolicyDef = res.getPolicyDefs().getPolicyDef("ExecutionPolicy");
+ ExecutionPolicy executionPolicy = policyHandler.getPolicy(executionPolicyDef, tx);
+ executionPolicy.execute(...);
+}
+
+
+
+
+