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The main module contains the GeoTools public interfaces that are used by other GeoTools modules (and GeoTools applications). Where possible we make use industry standard terms as provided by OGC and ISO standards. The formal GeoTools public api consists of gt-metadata, jts and the gt-main module. The main module contains the default implementations that are available provided to other GeoTools modules using our factory system. Factories are obtained from an appropriate FactoryFinder, giving applications a chance configure the factory used using the Factory Hints facilities. FilterFactory ff = CommonFactoryFinder.getFilterFactory(); Expression expr = ff.add( expression1, expression2 ); If you find yourself using implementation specific classes chances are you doing it wrong: Expression expr = new AddImpl( expression1, expressiom2 );

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/*
 *    GeoTools - The Open Source Java GIS Toolkit
 *    http://geotools.org
 *
 *    (C) 2008, Open Source Geospatial Foundation (OSGeo)
 *
 *    This library is free software; you can redistribute it and/or
 *    modify it under the terms of the GNU Lesser General Public
 *    License as published by the Free Software Foundation;
 *    version 2.1 of the License.
 *
 *    This library is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *    Lesser General Public License for more details.
 */
package org.geotools.data;

import java.io.Closeable;
import java.io.IOException;
import java.util.NoSuchElementException;
import org.opengis.feature.Feature;
import org.opengis.feature.type.FeatureType;

/**
 * The low-level interface for reading Features. Will use the underlying AttributeReader and the
 * given FeatureType to create new Features.
 *
 * Typical use is as follows:
 *
 * 

 *   FeatureReader reader = null;
 *   try{
 *      for( reader = data.getFeatureReader( filter ); reader.hasNext(); ){
 *          f = reader.next();
 *          ...
 *      }
 *   }
 *   catch (IOException problem){
 *      ...
 *   }
 *   finally {
 *      if( reader != null ){
 *          try {
 *             reader.close();
 *          }
 *          catch( IOException eek){
 *          }
 *      }
 *   }
 * 
 *
 * Questions and Suggestions
 *
 * 
 *   Q: Should FeatureReader provide access to the AttributeReaders it uses? 

 *       A: No, it looks like we will make a lazy Feature in order to cleanly allow for lazy parsing
 *       of attribtues.
 *   
Q:FeatureReader has a close method, but no open method? 

 *       A: This is by design allowing FeatureReader to encapsulate its InputStream or Rowset).
 *       Please assume that FeatureReaders are a single use proposition.
 *   
Q: All that exception handling is a pain! A: Yes it is, we have constructed semi-normal
 *       Java iterators to cut down on the pain. But you *do* still have to close 'em - this is IO
 *       after all.
 *   
Q: Can we include skip(int) - SeanG A: The order of the contents is not "known" or
 *       predicatable to the end user, so skip( int ) would be useless. For random access (a higher
 *       order of abstraction then FeatureReader) please look at FeatureList.
 * 
 *
 * @author Ian Schneider
 * @author Sean Geoghegan, Defence Science and Technology Organisation.
 * @version $Id$
 */
public interface FeatureReader extends Closeable {
    /**
     * Return the FeatureType this reader has been configured to create.
     *
     * @return the FeatureType of the Features this FeatureReader will create.
     */
    T getFeatureType();

    /**
     * Reads the next Feature in the FeatureReader.
     *
     * @return The next feature in the reader.
     * @throws IOException If an error occurs reading the Feature.
     * @throws IllegalAttributeException If the attributes read do not comply with the FeatureType.
     * @throws NoSuchElementException If there are no more Features in the Reader.
     */
    F next() throws IOException, IllegalArgumentException, NoSuchElementException;

    /**
     * Query whether this FeatureReader has another Feature.
     *
     * @return True if there are more Features to be read. In other words, true if calls to next
     *     would return a feature rather than throwing an exception.
     * @throws IOException If an error occurs determining if there are more Features.
     */
    boolean hasNext() throws IOException;

    /**
     * Release the underlying resources associated with this stream.
     *
     * @throws IOException if an I/O error occurs
     */
    void close() throws IOException;
}