179 lines
7.2 KiB
HTML
179 lines
7.2 KiB
HTML
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<title>Strolch: Policies</title>
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<div class="page-header">
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<h1 class="page-title">Documentation: Policies</h1>
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<p class="lead page-description">This page discusses the Strolch policies</p>
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</div>
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<div class="content">
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<p>Policies are an integral part when writing business logic in Strolch. In many cases it would suffice to write
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all such logic in <code>Services</code> and <code>Commands</code>, but as soon as behaviour can change,
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depending on the element being accessed, then this would quickly lead to many if/else blocks.</p>
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<p>Since writing large if/else blocks is not maintanable in the long run, Strolch offers a different approach.
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All Strolch elements can store Policy definitions. This is a simple key/value store where the key defines
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the type of policy, and the value references the policy to use.</p>
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<p>Currently there are two ways to reference a policy in Strolch, either via a key which defines a further
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lookup in the <code>PolicyHandler</code>, or directly as the name of the class to instantiate.</p>
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<p>Using policies in Strolch gives the additional possibility of easily changing the behaviour at runtime, as a
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Service and/or Command would delegate the behaviour to the currently configured policy on the releveant
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element.</p>
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<p>Policies are implemented by defining an abstract class and extends <code>StrolchPolicy</code>. This abstract
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class then defines the API of the actual policy. A concrete class then extends this abstract class and
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implements the concrete methods.</p>
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<p>Policies are registered on Resources, Orders, Activities and Actions. The following shows defining two
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policies on a Resource, a PlanningPolicy, an ExecutionPolicy in XML:</p>
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<pre>
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<Resource ...>
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...
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<Policies>
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<Policy Type="PlanningPolicy" Value="key:SimplePlanning" />
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<Policy Type="ExecutionPolicy" Value="java:li.strolch.policytest.TestSimulatedExecutionPolicy" />
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</Policies>
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</Resource></pre>
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<p><b>Note</b> how the PlanningPolicy has a value of <code>key:SimplePlanning</code> and the ExecutionPolicy
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defines a reference to an actual class.</p>
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<br/>
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<p>To use the PolicyHandler, it must be configured in the StrolchConfiguration.xml as follows:</p>
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<pre>
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<Component>
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<name>PolicyHandler</name>
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<api>li.strolch.policy.PolicyHandler</api>
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<impl>li.strolch.policy.DefaultPolicyHandler</impl>
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<Properties>
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<readPolicyFile>true</readPolicyFile>
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<policyConfigFile>StrolchPolicies.xml</policyConfigFile>
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</Properties>
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</Component></pre>
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<br/>
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<p>And this policy handler implementation requires a file where the lookups for the policies is defined,
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e.g.:</p>
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<pre>
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<StrolchPolicies>
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<PolicyType Type="PlanningPolicy" Api="li.strolch.policytest.TestPlanningPolicy">
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<Policy Key="SimplePlanning" Class="li.strolch.policytest.TestSimplePlanningPolicy" />
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</PolicyType>
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<PolicyType Type="ConfirmationPolicy" Api="li.strolch.policytest.TestConfirmationPolicy">
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<Policy Key="NoConfirmation" Class="li.strolch.policytest.TestNoConfirmationPolicy" />
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</PolicyType>
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</StrolchPolicies></pre>
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<br/>
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<p>Now at runtime we can access the policies:</p>
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<pre>
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PolicyHandler policyHandler = getComponent(PolicyHandler.class);
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try (StrolchTransaction tx = openTx()) {
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Resource res = tx.getResourceBy("TestType", "MyTestResource");
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PolicyDefs policyDefs = res.getPolicyDefs();
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PolicyDef planningPolicyDef = policyDefs.getPolicyDef("PlanningPolicy");
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PlanningPolicy planningPolicy = policyHandler.getPolicy(planningPolicyDef, tx);
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planningPolicy.plan(...);
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PolicyDef executionPolicyDef = res.getPolicyDefs().getPolicyDef("ExecutionPolicy");
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ExecutionPolicy executionPolicy = policyHandler.getPolicy(executionPolicyDef, tx);
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executionPolicy.execute(...);
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}</pre>
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