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| |
| <h1>CDI Dynamic Inject</h1> |
| </div> |
| </div> |
| </div> |
| <div class="row"> |
| |
| <div class="col-md-12"> |
| <div id="preamble"> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>: jbake-type: page |
| : jbake-status: published</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_introduction">Introduction</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>Sometimes we need to write multiple implementations for a business rules interface, to increase decoupling we will dynamically inject the implementation at runtime.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_example_1">Example 1</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>In this example we have a <code>Payment</code> interface and its implementations:</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p>Cash</p> |
| </li> |
| <li> |
| <p>CreditCard</p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>In our test (<code>FinalizePaymentTest</code>) we injected the FinalizePayment class, and called the <code>finishWithCash</code> method.</p> |
| </div> |
| <div class="paragraph"> |
| <p>This method will dynamically inject the correct implementation using CDI features.</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code class="language-java" data-lang="java">public String finishWithCash () { |
| |
| paymentChoosed = paymentsLazy.select(Cash.class).get (); |
| return paymentChoosed.pay (); |
| }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>note that a variable called <code>paymentsLazy</code> is variable will contain all implementations of the <code>Payment</code> interface</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code class="language-java" data-lang="java">@Inject |
| @Any |
| private Instance <Payment> paymentsLazy;</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>In this variable we are using:</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p>Annotation <code>@inject</code></p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>Indicates to CDI that we need a dependency injection</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p>Annotation <code>@Any</code></p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>Indicate that all possible implementations should be listed.</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p><code>Instance</code> object</p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>Object responsible for knowing all possible implementations and instantiating them at the desired time.</p> |
| </div> |
| <div class="paragraph"> |
| <p>With this variable ready we can call it using:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code class="language-java" data-lang="java">paymentsLazy.select(Cash.class).get ();</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>where <code>Cash.class</code> tells you the implementation and <code>.get()</code> returns the ready-to-use instance.</p> |
| </div> |
| </div> |
| </div> |
| <div class="sect1"> |
| <h2 id="_example_2">Example 2</h2> |
| <div class="sectionbody"> |
| <div class="paragraph"> |
| <p>In this example we have a <code>Payment</code> interface and its implementations:</p> |
| </div> |
| <div class="ulist"> |
| <ul> |
| <li> |
| <p>Cash</p> |
| </li> |
| <li> |
| <p>CreditCard</p> |
| </li> |
| </ul> |
| </div> |
| <div class="paragraph"> |
| <p>In our test (<code>FinalizePaymentQualifierTest</code>) we injected the FinalizePayment class, and called the <code>finishByQualifier</code> method.</p> |
| </div> |
| <div class="paragraph"> |
| <p>This method will dynamically inject the correct implementation using a <code>Qualifier</code> (PaymentType).</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code class="language-java" data-lang="java">public String finishByQualifier (PaymentType type) { |
| |
| paymentChoosed = paymentsLazy.select (new PayByQualifier (type)) .get (); |
| return paymentChoosed.pay (); |
| }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>For this approach to work we will need to create a new class called <code>PayByQualifier</code> that extends <code>AnnotationLiteral</code> that expects a qualifier to pass into its <code>T extends Annotation</code> (Generics) parameter.</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code class="language-java" data-lang="java">public class PayByQualifier extends AnnotationLiteral <PaymentQualifier> implements PaymentQualifier { |
| |
| private PaymentType type; |
| |
| public PayByQualifier (PaymentType type) { |
| this.type = type; |
| } |
| |
| @Override |
| public PaymentType type () { |
| return this.type; |
| } |
| }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>the important thing is to implement the Annotation method in our case the <code>public PaymentType type();</code></p> |
| </div> |
| <div class="paragraph"> |
| <p>To facilitate this implementation we receive this value from constructor class.</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code class="language-java" data-lang="java">public PayByQualifier (PaymentType type) { |
| |
| this.type = type; |
| }</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>With this class ready we can use it in our business class:</p> |
| </div> |
| <div class="listingblock"> |
| <div class="content"> |
| <pre class="highlight"><code class="language-java" data-lang="java">paymentChoosed = paymentsLazy.select (new PayByQualifier(type)).get ();</code></pre> |
| </div> |
| </div> |
| <div class="paragraph"> |
| <p>Obs: The qualifier structure was reused from <a href="https://github.com/cassunde/tomee/tree/master/examples/cdi-qualifier" class="bare">https://github.com/cassunde/tomee/tree/master/examples/cdi-qualifier</a> project</p> |
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