org.eclipse.rdf4j.common.iteration.ExceptionConvertingIteration Maven / Gradle / Ivy

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/*******************************************************************************
 * Copyright (c) 2015 Eclipse RDF4J contributors, Aduna, and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Distribution License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *******************************************************************************/

package org.eclipse.rdf4j.common.iteration;

import java.util.NoSuchElementException;

/**
 * A CloseableIteration that converts an arbitrary iteration to an iteration with exceptions of type
 * X. Subclasses need to override {@link #convert(Exception)} to do the conversion.
 */
public abstract class ExceptionConvertingIteration
		extends AbstractCloseableIteration
{

	/*-----------*
	 * Variables *
	 *-----------*/

	/**
	 * The underlying Iteration.
	 */
	private final Iteration iter;

	/*--------------*
	 * Constructors *
	 *--------------*/

	/**
	 * Creates a new ExceptionConvertingIteration that operates on the supplied iteration.
	 * 
	 * @param iter
	 *        The Iteration that this ExceptionConvertingIteration operates on, must not be
	 *        null.
	 */
	public ExceptionConvertingIteration(Iteration iter) {
		assert iter != null;
		this.iter = iter;
	}

	/*---------*
	 * Methods *
	 *---------*/

	/**
	 * Converts an exception from the underlying iteration to an exception of type X.
	 */
	protected abstract X convert(Exception e);

	/**
	 * Checks whether the underlying Iteration contains more elements.
	 * 
	 * @return true if the underlying Iteration contains more elements, false otherwise.
	 * @throws X
	 */
	public boolean hasNext()
		throws X
	{
		try {
			return iter.hasNext();
		}
		catch (Exception e) {
			throw convert(e);
		}
	}

	/**
	 * Returns the next element from the wrapped Iteration.
	 * 
	 * @throws X
	 * @throws java.util.NoSuchElementException
	 *         If all elements have been returned.
	 * @throws IllegalStateException
	 *         If the Iteration has been closed.
	 */
	public E next()
		throws X
	{
		try {
			return iter.next();
		}
		catch (NoSuchElementException e) {
			throw e;
		}
		catch (IllegalStateException e) {
			throw e;
		}
		catch (Exception e) {
			throw convert(e);
		}
	}

	/**
	 * Calls remove() on the underlying Iteration.
	 * 
	 * @throws UnsupportedOperationException
	 *         If the wrapped Iteration does not support the remove operation.
	 * @throws IllegalStateException
	 *         If the Iteration has been closed, or if {@link #next} has not yet been called, or
	 *         {@link #remove} has already been called after the last call to {@link #next}.
	 */
	public void remove()
		throws X
	{
		try {
			iter.remove();
		}
		catch (UnsupportedOperationException e) {
			throw e;
		}
		catch (IllegalStateException e) {
			throw e;
		}
		catch (Exception e) {
			throw convert(e);
		}
	}

	/**
	 * Closes this Iteration as well as the wrapped Iteration if it happens to be a {@link CloseableIteration}
	 * .
	 */
	@Override
	protected void handleClose()
		throws X
	{
		super.handleClose();

		try {
			Iterations.closeCloseable(iter);
		}
		catch (Exception e) {
			throw convert(e);
		}
	}
}