Full text search engines like Apache Lucene™ are a very powerful technology to bring free text/efficient queries to applications. If suffers several mismatches when dealing with an object domain model (keeping the index up to date, mismatch between the index structure and the domain model, querying mismatch...) Hibernate Search indexes your domain model thanks to a few annotations, takes care of the database / index synchronization and brings you back regular managed objects from free text queries. Hibernate Search is using Apache Lucene under the cover.

Hibernate Search has been designed to integrates nicely and as naturally as possible with JPA and Hibernate. As a natural extension, JBoss Seam provides an Hibernate Search integration.

Please refer to the Hibernate Search documentation for information specific to the Hibernate Search project.

Hibernate Search is configured either in the META-INF/persistence.xml or hibernate.cfg.xml file.

Hibernate Search configuration has sensible defaults for most configuration parameters, Here is a description of the minimal configuration to get started.

   <persistence-unit name="sample">
      <jta-data-source>java:/DefaultDS</jta-data-source>
      <properties>
         [...]
         <!-- use a file system based index -->
         <property name="hibernate.search.default.directory_provider" 
                   value="org.hibernate.search.store.FSDirectoryProvider"/>
         <!-- directory where the indexes will be stored -->
         <property name="hibernate.search.default.indexBase" 
                   value="/Users/prod/apps/dvdstore/dvdindexes"/>
      </properties>
   </persistence-unit>

If you plan to target Hibernate Annotations or EntityManager 3.2.x (embedded into JBoss AS 4.2.GA), you also need to configure the appropriate event listeners.

   <persistence-unit name="sample">
      <jta-data-source>java:/DefaultDS</jta-data-source>
      <properties>
         [...]
         <!-- use a file system based index -->
         <property name="hibernate.search.default.directory_provider" 
                   value="org.hibernate.search.store.FSDirectoryProvider"/>
         <!-- directory where the indexes will be stored -->
         <property name="hibernate.search.default.indexBase" 
                   value="/Users/prod/apps/dvdstore/dvdindexes"/>

         <property name="hibernate.ejb.event.post-insert" 
                   value="org.hibernate.search.event.FullTextIndexEventListener"/>
         <property name="hibernate.ejb.event.post-update" 
                   value="org.hibernate.search.event.FullTextIndexEventListener"/>
         <property name="hibernate.ejb.event.post-delete" 
                   value="org.hibernate.search.event.FullTextIndexEventListener"/>

      </properties>
   </persistence-unit>

In addition to the configuration file, the following jars have to be deployed:

Hibernate Search uses annotations to map entities to a Lucene index, check the reference documentation for more informations.

Hibernate Search is fully integrated with the API and semantic of JPA / Hibernate. Switching from a HQL or Criteria based query requires just a few lines of code. The main API the application interacts with is the FullTextSession API (subclass of Hibernate's Session).

When Hibernate Search is present, JBoss Seam injects a FullTextSession.

@Stateful
@Name("search")
public class FullTextSearchAction implements FullTextSearch, Serializable
{   
   @In
   FullTextSession session;

   public void search(String searchString) {
      org.apache.lucene.query.Query luceneQuery = getLuceneQuery();
      org.hibernate.Query query session.createFullTextQuery(luceneQuery, Product.class);
      searchResults = query
            .setMaxResults(pageSize + 1)
            .setFirstResult(pageSize * currentPage)
            .list();
   }
   [...]
}  

If the Java Persistence API is used, a smoother integration is proposed.

@Name("search")
public class FullTextSearchAction implements FullTextSearch, Serializable
{   
   @In
   FullTextEntityManager em;

   public void search(String searchString) {
      org.apache.lucene.query.Query luceneQuery = getLuceneQuery();
      javax.persistence.Query query = em.createFullTextQuery(luceneQuery, Product.class);
      searchResults = query
            .setMaxResults(pageSize + 1)
            .setFirstResult(pageSize * currentPage)
            .getResultList();
   }
   [...]
}  

When Hibernate Search is present, a FulltextEntityManager is injected. FullTextEntityManager extends EntityManager with search specific methods, the same way FullTextSession extends Session.

When an EJB 3.0 Session or Message Driven Bean injection is used (ie Bean using @PersistenceContext), it is not possible to replace the EntityManager interface by the FullTextEntityManager interface in the declaration statement. However, the implementation injected will be a FullTextEntityManager implementation: downcasting is then possible.

@Stateful
@Name("search")
public class FullTextSearchAction implements FullTextSearch, Serializable
{   
   @PersistenceContext
   EntityManager em;

   public void search(String searchString) {
      org.apache.lucene.query.Query luceneQuery = getLuceneQuery();
      FullTextEntityManager ftEm = (FullTextEntityManager) em;
      javax.persistence.Query query = ftEm.createFullTextQuery(luceneQuery, Product.class);
      searchResults = query
            .setMaxResults(pageSize + 1)
            .setFirstResult(pageSize * currentPage)
            .getResultList();
   }
   [...]
}  

Check the DVDStore or the blog examples of the JBoss Seam distribution for a concrete use of Hibernate Search.