package org.springframework.batch.item.file;
   
   import java.util.Arrays;
   import java.util.concurrent.atomic.AtomicInteger;
   
   import org.springframework.batch.item.ExecutionContext;
   import org.springframework.batch.item.ItemReader;
   import org.springframework.batch.item.ItemStreamException;
   import org.springframework.batch.item.ItemStreamReader;
  import org.springframework.batch.item.util.ExecutionContextUserSupport;
  import org.springframework.core.io.Resource;
  import org.springframework.core.io.support.ResourceArrayPropertyEditor;
  
  /**
   * {@link ItemReader} which produces {@link Resource} instances from an array.
   * This can be used conveniently with a configuration entry that injects a
   * pattern (e.g. <code>mydir/*.txt</code>, which can then be converted by Spring
   * to an array of Resources by the ApplicationContext.
   * 
   * <br/>
   * <br/>
   * 
   * Thread safe between calls to {@link #open(ExecutionContext)}. The
   * {@link ExecutionContext} is not accurate in a multi-threaded environment, so
   * do not rely on that data for restart (i.e. always open with a fresh context).
   * 
   * @author Dave Syer
   * 
   * @see ResourceArrayPropertyEditor
   * 
   * @since 2.1
   */
  public class ResourcesItemReader extends ExecutionContextUserSupport implements ItemStreamReader<Resource> {
  
  	private Resource[] resources = new Resource[0];
  
  	private AtomicInteger counter = new AtomicInteger(0);
  
  	{
  		/*
  		 * Initialize the name for the key in the execution context.
  		 */
  		setName(getClass().getName());
  	}
  
  	/**
  	 * The resources to serve up as items. Hint: use a pattern to configure.
  	 * 
  	 * @param resources the resources
  	 */
  	public void setResources(Resource[] resources) {
  		this.resources = Arrays.asList(resources).toArray(new Resource[resources.length]);
  	}
  
  	/**
  	 * Increments a counter and returns the next {@link Resource} instance from
  	 * the input, or null if none remain.
  	 */
      @Override
  	public synchronized Resource read() throws Exception {
  		int index = counter.incrementAndGet() - 1;
  		if (index >= resources.length) {
  			return null;
  		}
  		return resources[index];
  	}
  
      @Override
  	public void close() throws ItemStreamException {
  	}
  
      @Override
  	public void open(ExecutionContext executionContext) throws ItemStreamException {
  		counter.set(executionContext.getInt(getKey("COUNT"), 0));
  	}
  
      @Override
  	public void update(ExecutionContext executionContext) throws ItemStreamException {
  		executionContext.putInt(getKey("COUNT"), counter.get());
  	}
  
  }