Add some javadoc

src/main/java/org/springframework/samples/petclinic/repository/jdbc/JdbcPetVisitExtractor.java

@@ -16,11 +16,16 @@
 package org.springframework.samples.petclinic.repository.jdbc;
 
 import org.springframework.data.jdbc.core.OneToManyResultSetExtractor;
+import org.springframework.jdbc.core.ResultSetExtractor;
 import org.springframework.samples.petclinic.model.Visit;
 
 import java.sql.ResultSet;
 import java.sql.SQLException;
 
+/**
+ * {@link ResultSetExtractor} implementation by using the
+ * {@link OneToManyResultSetExtractor} of Spring Data Core JDBC Extensions.
+ */
 public class JdbcPetVisitExtractor extends
         OneToManyResultSetExtractor<JdbcPet, Visit, Integer> {
 
@@ -37,8 +42,7 @@ public class JdbcPetVisitExtractor extends
     protected Integer mapForeignKey(ResultSet rs) throws SQLException {
         if (rs.getObject("visits.pet_id") == null) {
             return null;
-        }
+        } else {
-        else {
             return rs.getInt("visits.pet_id");
         }
     }

src/main/java/org/springframework/samples/petclinic/repository/jdbc/JdbcVisitRowMapper.java

@@ -24,6 +24,10 @@ import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.util.Date;
 
+/**
+ * {@link RowMapper} implementation mapping data from a {@link ResultSet} to the corresponding properties
+ * of the {@link Visit} class.
+ */
 class JdbcVisitRowMapper implements RowMapper<Visit> {
 
     @Override