title: Spring boot autowiring an interface with multiple implementations
body: <p>In normal Spring, when we want to autowire an interface, we define it's implementation in Spring context file.</p>
  <ol>
  <li>What about Spring boot?</li>
  <li>how can we achieve this?</li>
  </ol>
  <p>currently we only autowire classes that are not interfaces.</p>
  <p>Another part of this question is about using a class in a Junit class inside a Spring boot project.</p>
  <p>If we want to use a CalendarUtil for example, if we autowire CalendarUtil, it will throw a null pointer exception. What can we do in this case? I just initialized using &quot;new&quot; for now...</p>