Spring Batch - Spring Enterprise Recipes: A Problem Solution Approach - page 363

public UserRegistration read() throws Exception,UnexpectedInputException,
ParseException {
Date today = new Date();
Collection<UserRegistration> registrations =
userRegistrationService.getOutstandingUserRegistrationBatchForDate(
1, today);
if (registrations!=null && registrations.size() >= 1)
return registrations.iterator().next();
return null;
}
}
As you can see, the interface is trivial. In this case, you defer most work to a remote service to
provide you with the input. The interface requires that you return one record. The interface is
parameterized to the type of object (the “item”) to be returned. All the read items will be aggregated
and then passed to the ItemWriter .
Writing a Custom ItemWriter
The ItemWriter example is also trivial. Imagine wanting to “write” by invoking a remote service using
any of the vast support for remoting that Spring provides. The ItemWriter interface is parameterized
by the type of item you're expecting to write. Here, you expect a UserRegistration object from the
ItemReader . The interface consists of one method, which expects a List of the class's parameterized
type. These are the objects read from ItemReader and aggregated. If your commit-interval were ten, then
you might expect ten or fewer items in the List .
import java.util.List;
import org.apache.commons.lang.builder.ToStringBuilder;
import org.apache.log4j.Logger;
import org.springframework.batch.item.ItemWriter;
import org.springframework.beans.factory.annotation.Autowired;
import com.apress.springenterpriserecipes.springbatch.User;
import com.apress.springenterpriserecipes.springbatch.UserRegistrationService;
import com.apress.springenterpriserecipes.springbatch.solution1.UserRegistration;
/**
*
*
* This class writes the user registration by calling an RPC service (whose
* client interface is wired in using Spring
*/
public class UserRegistrationServiceItemWriter implements
ItemWriter<UserRegistration> {
private static final Logger logger = Logger
.getLogger(UserRegistrationServiceItemWriter.class);