Adding a Search Service to a Java Application

Finally, we alert jPetStore to the new controller’s existence. If jPetStoreis not coded for extensibility, we have to modify the application code in order to get it to work. For instance, if there are methods ofjPetStorethat create instances ofSearchProductsControllerdirectly, we must change each of those lines to create aSearchPagesControllerinstead.

It turns out, however, thatjPetStoreis quite ready for extensibility—partly because it is based on the Spring framework. In order to telljPetStoreabout our new controller, we modify a single configuration file (petstore-servlets.xml). This file tells Spring what objects to create and how to wire them together to make a sensible application. Now, we just need to find the configuration setting used to launch theSearchProductsControllerand point it to our newSearchPagesControllerinstead.

  <bean name="/shop/searchProducts.do"
      class="org.springframework.samples. jpetstore.web.spring.SearchPagesController">
      <property name="petStore"><ref bean="petStore"/></property>
  </bean>

We’re telling the application to map requests for “/shop/searchProducts.do” to a new instance ofSearchPagesController. At the same time, we tell it, provide theSearchPagesControllerwith the current instance ofpetStore(in a property calledpetStore).

1. Keep it simple: the controller logic is a simple invocation of Spider; the controller interface is very simple (one method)
   
2. Choose the right tools: Spring and the Spider
   
3. Do one thing and do it well: since the Spider is so well-encapsulated, it’s easy to add to an existing service; the controller deals with invoking the Spider and the JSP only needs to display the results—MVC pattern well-demonstrated
   
4. Strive for transparency: the site doesn’t care how it is indexed; it can easily switch between data-driven and HTML-driven search technologies
   
5. Allow for extension: we quickly expanded our search capabilities by adding a new tool with minimal code; the configuration abilities of jPetStore allow for no-code recognition of new service

Please check back next week for the continuation of this article.