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cases it would suffice to write all such logic in <code>Services</code> and <code>Commands</code>, but
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as soon as behaviour can change, depending on the element being accessed, then
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this would quickly lead to many if/else blocks.</p><p>Since writing large if/else blocks is not maintanable in the long run, Strolch
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offers a different approach. All Strolch elements can store Policy definitions.
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This is a simple key/value store where the key defines the type of policy, and
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the value references the policy to use.</p><p>Currently there are two ways to reference a policy in Strolch, either via a key
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which defines a further lookup in the <code>PolicyHandler</code>, or directly as the name
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of the class to instantiate.</p><p>Using policies in Strolch gives the additional possibility of easily changing
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the behaviour at runtime, as a Service and/or Command would delegate the
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behaviour to the currently configured policy on the releveant element.</p><p>Policies are implemented by defining an abstract class and extends
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StrolchPolicy. This abstract class then defines the API of the actual policy. A
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concrete class then extends this abstract class and implements the concrete
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methods.</p><p>Policies are registered on Resources, Orders, Activities and Actions. The
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following shows defining two policies on a Resource, a PlanningPolicy, an
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ExecutionPolicy in XML:</p><div class=highlight><pre style=color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-xml data-lang=xml><span style=color:#f92672><Resource</span> <span style=color:#960050;background-color:#1e0010>...</span><span style=color:#f92672>></span>
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...
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<span style=color:#f92672><Policies></span>
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<span style=color:#f92672><Policy</span> <span style=color:#a6e22e>Type=</span><span style=color:#e6db74>"PlanningPolicy"</span> <span style=color:#a6e22e>Value=</span><span style=color:#e6db74>"key:SimplePlanning"</span> <span style=color:#f92672>/></span>
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<span style=color:#f92672><Policy</span> <span style=color:#a6e22e>Type=</span><span style=color:#e6db74>"ExecutionPolicy"</span> <span style=color:#a6e22e>Value=</span><span style=color:#e6db74>"java:li.strolch.policytest.TestSimulatedExecutionPolicy"</span> <span style=color:#f92672>/></span>
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<span style=color:#f92672></Policies></span>
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<span style=color:#f92672></Resource></span>
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</code></pre></div><div class="notices tip"><p>Note how the PlanningPolicy has a value of key:SimplePlanning
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and the ExecutionPolicy defines a reference to an actual class.</p></div><p>To use the PolicyHandler, it must be configured in the StrolchConfiguration.xml
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as follows:</p><div class=highlight><pre style=color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-xml data-lang=xml>
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<span style=color:#f92672><Component></span>
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<span style=color:#f92672><name></span>PolicyHandler<span style=color:#f92672></name></span>
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<span style=color:#f92672><api></span>li.strolch.policy.PolicyHandler<span style=color:#f92672></api></span>
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<span style=color:#f92672><impl></span>li.strolch.policy.DefaultPolicyHandler<span style=color:#f92672></impl></span>
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<span style=color:#f92672><Properties></span>
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<span style=color:#f92672><readPolicyFile></span>true<span style=color:#f92672></readPolicyFile></span>
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<span style=color:#f92672><policyConfigFile></span>StrolchPolicies.xml<span style=color:#f92672></policyConfigFile></span>
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<span style=color:#f92672></Properties></span>
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<span style=color:#f92672></Component></span>
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</code></pre></div><p>And this policy handler implementation requires a file where the lookups for the
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policies is defined, e.g.:</p><div class=highlight><pre style=color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-xml data-lang=xml>
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<span style=color:#f92672><StrolchPolicies></span>
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<span style=color:#f92672><PolicyType</span> <span style=color:#a6e22e>Type=</span><span style=color:#e6db74>"PlanningPolicy"</span>
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<span style=color:#a6e22e>Api=</span><span style=color:#e6db74>"li.strolch.policytest.TestPlanningPolicy"</span><span style=color:#f92672>></span>
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<span style=color:#f92672><Policy</span> <span style=color:#a6e22e>Key=</span><span style=color:#e6db74>"SimplePlanning"</span>
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<span style=color:#a6e22e>Class=</span><span style=color:#e6db74>"li.strolch.policytest.TestSimplePlanningPolicy"</span><span style=color:#f92672>/></span>
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<span style=color:#f92672></PolicyType></span>
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<span style=color:#f92672><PolicyType</span> <span style=color:#a6e22e>Type=</span><span style=color:#e6db74>"ConfirmationPolicy"</span>
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<span style=color:#a6e22e>Api=</span><span style=color:#e6db74>"li.strolch.policytest.TestConfirmationPolicy"</span><span style=color:#f92672>></span>
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<span style=color:#f92672><Policy</span> <span style=color:#a6e22e>Key=</span><span style=color:#e6db74>"NoConfirmation"</span>
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<span style=color:#a6e22e>Class=</span><span style=color:#e6db74>"li.strolch.policytest.TestNoConfirmationPolicy"</span><span style=color:#f92672>/></span>
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<span style=color:#f92672></PolicyType></span>
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<span style=color:#f92672></StrolchPolicies></span>
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</code></pre></div><p>Now at runtime we can access the policies:</p><div class=highlight><pre style=color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4><code class=language-java data-lang=java>PolicyHandler policyHandler<span style=color:#f92672>=</span>getComponent<span style=color:#f92672>(</span>PolicyHandler<span style=color:#f92672>.</span><span style=color:#a6e22e>class</span><span style=color:#f92672>);</span>
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<span style=color:#66d9ef>try</span><span style=color:#f92672>(</span>StrolchTransaction tx<span style=color:#f92672>=</span>openTx<span style=color:#f92672>()){</span>
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Resource res<span style=color:#f92672>=</span>tx<span style=color:#f92672>.</span><span style=color:#a6e22e>getResourceBy</span><span style=color:#f92672>(</span><span style=color:#e6db74>"TestType"</span><span style=color:#f92672>,</span><span style=color:#e6db74>"MyTestResource"</span><span style=color:#f92672>);</span>
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PolicyDefs policyDefs<span style=color:#f92672>=</span>res<span style=color:#f92672>.</span><span style=color:#a6e22e>getPolicyDefs</span><span style=color:#f92672>();</span>
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PolicyDef planningPolicyDef<span style=color:#f92672>=</span>policyDefs<span style=color:#f92672>.</span><span style=color:#a6e22e>getPolicyDef</span><span style=color:#f92672>(</span><span style=color:#e6db74>"PlanningPolicy"</span><span style=color:#f92672>);</span>
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PlanningPolicy planningPolicy<span style=color:#f92672>=</span>policyHandler<span style=color:#f92672>.</span><span style=color:#a6e22e>getPolicy</span><span style=color:#f92672>(</span>planningPolicyDef<span style=color:#f92672>,</span>tx<span style=color:#f92672>);</span>
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planningPolicy<span style=color:#f92672>.</span><span style=color:#a6e22e>plan</span><span style=color:#f92672>(...);</span>
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PolicyDef executionPolicyDef<span style=color:#f92672>=</span>res<span style=color:#f92672>.</span><span style=color:#a6e22e>getPolicyDefs</span><span style=color:#f92672>().</span><span style=color:#a6e22e>getPolicyDef</span><span style=color:#f92672>(</span><span style=color:#e6db74>"ExecutionPolicy"</span><span style=color:#f92672>);</span>
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ExecutionPolicy executionPolicy<span style=color:#f92672>=</span>policyHandler<span style=color:#f92672>.</span><span style=color:#a6e22e>getPolicy</span><span style=color:#f92672>(</span>executionPolicyDef<span style=color:#f92672>,</span>tx<span style=color:#f92672>);</span>
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executionPolicy<span style=color:#f92672>.</span><span style=color:#a6e22e>execute</span><span style=color:#f92672>(...);</span>
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<span style=color:#f92672>}</span>
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</code></pre></div><footer class=footline></footer></div></div><div id=navigation><a class="nav nav-prev" href=/documentation/transactions/ title=Transactions><i class="fa fa-chevron-left"></i></a><a class="nav nav-next" href=/documentation/observers/ title=Observers style=margin-right:0><i class="fa fa-chevron-right"></i></a></div></section><div style=left:-1000px;overflow:scroll;position:absolute;top:-1000px;border:none;box-sizing:content-box;height:200px;margin:0;padding:0;width:200px><div style=border:none;box-sizing:content-box;height:200px;margin:0;padding:0;width:200px></div></div><script src=/js/clipboard.min.js?1626091328></script><script src=/js/perfect-scrollbar.min.js?1626091328></script><script src=/js/perfect-scrollbar.jquery.min.js?1626091328></script><script src=/js/jquery.sticky.js?1626091328></script><script src=/js/featherlight.min.js?1626091328></script><script src=/js/highlight.pack.js?1626091328></script><script>hljs.initHighlightingOnLoad();</script><script src=/js/modernizr.custom-3.6.0.js?1626091328></script><script src=/js/learn.js?1626091328></script><script src=/js/hugo-learn.js?1626091328></script><script src=/mermaid/mermaid.js?1626091328></script><script>mermaid.initialize({startOnLoad:true});</script></body></html> |