9.2.7.4. Override an Injection with an Alternative

Summary

Alternative beans let you override existing beans. They can be thought of as a way to plug in a class which fills the same role, but functions differently. They are disabled by default. This task shows you how to specify and enable an alternative.

Procedure 9.5. Override an Injection

This task assumes that you already have a TranslatingWelcome class in your project, but you want to override it with a "mock" TranslatingWelcome class. This would be the case for a test deployment, where the true Translator bean cannot be used.

  1. Define the alternative.

    @Alternative
@Translating 
public class MockTranslatingWelcome extends Welcome {
  public String buildPhrase(string city) {
    return "Bienvenue à " + city + "!");
  }
}

  2. Substitute the alternative.

    To activate the substitute implementation, add the fully-qualified class name to your META-INF/beans.xml or WEB-INF/beans.xml file. 
    <beans>
  <alternatives>
    <class>com.acme.MockTranslatingWelcome</class>
  </alternatives>
</beans>
Result

The alternative implementation is now used instead of the original one.

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