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<!DOCTYPE html>
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<title>Using Qualifiers</title>
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<b>Java Platform, Enterprise Edition (Java EE) 8</b><br />
<b>The Java EE Tutorial</b>
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<p><a id="GJBCK"></a><a id="using-qualifiers"></a></p>
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<div class="sect1">
<h2 id="_using_qualifiers">Using Qualifiers</h2>
<div class="sectionbody">
<div class="paragraph">
<p>You can use qualifiers to provide various implementations of a
particular bean type. A qualifier is an annotation that you apply to a
bean. A qualifier type is a Java annotation defined as
<code>@Target({METHOD, FIELD, PARAMETER, TYPE})</code> and <code>@Retention(RUNTIME)</code>.</p>
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<div class="paragraph">
<p>For example, you could declare an <code>@Informal</code> qualifier type and apply
it to another class that extends the <code>Greeting</code> class. To declare this
qualifier type, use the following code:</p>
</div>
<div class="listingblock">
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<pre class="prettyprint highlight"><code class="language-oac_no_warn" data-lang="oac_no_warn">package greetings;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.ElementType.PARAMETER;
import static java.lang.annotation.ElementType.TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import java.lang.annotation.Retention;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import java.lang.annotation.Target;
import javax.inject.Qualifier;
@Qualifier
@Retention(RUNTIME)
@Target({TYPE, METHOD, FIELD, PARAMETER})
public @interface Informal {}</code></pre>
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</div>
<div class="paragraph">
<p>You can then define a bean class that extends the <code>Greeting</code> class and
uses this qualifier:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-oac_no_warn" data-lang="oac_no_warn">package greetings;
@Informal
public class InformalGreeting extends Greeting {
public String greet(String name) {
return "Hi, " + name + "!";
}
}</code></pre>
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<div class="paragraph">
<p>Both implementations of the bean can now be used in the application.</p>
</div>
<div class="paragraph">
<p>If you define a bean with no qualifier, then the bean automatically has the
qualifier <code>@Default</code>. The unannotated <code>Greeting</code> class could be declared
as follows:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-oac_no_warn" data-lang="oac_no_warn">package greetings;
import javax.enterprise.inject.Default;
@Default
public class Greeting {
public String greet(String name) {
return "Hello, " + name + ".";
}
}</code></pre>
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