NaturalLanguageDocumentUrl.java

/*
   This file is part of the LarKC platform 
   http://www.larkc.eu/

   Copyright 2010 LarKC project consortium

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
 */
package eu.larkc.core.data;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

/**
 * Implementation of Natural Language Document which is stored as URL and
 * retrieves the content when needed, once retrieved content is cached
 *
 * @author Blaz Fortuna
 *
 */
public class NaturalLanguageDocumentUrl implements NaturalLanguageDocument {

	// link to document
	private String urlStr;
	// retrieved document
	private String documentStr;

	private String convertStreamToString(InputStream is) {
		/*
		 * To convert the InputStream to String we use the
		 * BufferedReader.readLine() method. We iterate until the BufferedReader
		 * return null which means there's no more data to read. Each line will
		 * appended to a StringBuilder and returned as String.
		 */
		BufferedReader reader = new BufferedReader(new InputStreamReader(is));
		StringBuilder sb = new StringBuilder();

		String line = null;
		try {
			while ((line = reader.readLine()) != null) {
				sb.append(line + "\n");
			}
		} catch (IOException e) {
			// handle errors ...
		} finally {
			try {
				is.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}

		return sb.toString();
	}

	// retrieves link stored in urlStr and stores the content in the documentStr
	private void retrieve() {
		try {
			URL url = new URL(urlStr);
			if (url.getProtocol().equals("http")) {
				// connect to the web server
				HttpURLConnection connection = (HttpURLConnection) url
						.openConnection();
				connection.setRequestMethod("GET");
				connection.connect();
				// retrieve the content
				InputStream stream = connection.getInputStream();
				documentStr = convertStreamToString(stream);
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	public NaturalLanguageDocumentUrl(String _urlStr) {
		urlStr = _urlStr;
		documentStr = null;
	}

	public String getText() {
		if (documentStr == null) {
			retrieve();
		}
		return documentStr;
	}

	public String getUrl() {
		return urlStr;
	}

	/* (non-Javadoc)
	 * @see eu.larkc.core.data.InformationSet#toRDF(eu.larkc.core.data.SetOfStatements)
	 */
	@Override
	public SetOfStatements toRDF(SetOfStatements data) {
		throw new RuntimeException("Not implemented!");
	}
}