SimpleHTMLTagsFilter.java

/**
 * <a href="http://www.openolat.org">
 * OpenOLAT - Online Learning and Training</a><br>
 * <p>
 * Licensed under the Apache License, Version 2.0 (the "License"); <br>
 * you may not use this file except in compliance with the License.<br>
 * You may obtain a copy of the License at the
 * <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache homepage</a>
 * <p>
 * Unless required by applicable law or agreed to in writing,<br>
 * software distributed under the License is distributed on an "AS IS" BASIS, <br>
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. <br>
 * See the License for the specific language governing permissions and <br>
 * limitations under the License.
 * <p>
 * Initial code contributed and copyrighted by<br>
 * frentix GmbH, http://www.frentix.com
 * <p>
 */
package org.olat.core.util.filter.impl;

import java.io.IOException;
import java.io.StringReader;

import org.cyberneko.html.parsers.SAXParser;
import org.olat.core.logging.OLog;
import org.olat.core.logging.Tracing;
import org.olat.core.util.StringHelper;
import org.olat.core.util.filter.Filter;
import org.olat.core.util.io.LimitedContentWriter;
import org.olat.search.service.document.file.FileDocumentFactory;
import org.xml.sax.Attributes;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

/**
 * Description:<br>
 * The html tags filter takes a string and filters all HTML tags. The filter
 * does not remove the code within the tags, only the tag itself. Example:
 * '<font color="red">hello</font>world' will become 'hello world'
 * <p>
 * The filter might not be perfect, its a simple version. All tag attributes
 * will be removed as well.
 * <p>
 * Use the SimpleHTMLTagsFilterTest to add new testcases that must work with 
 * this filter.
 * 
 * <P>
 * Initial Date: 15.07.2009 <br>
 * 
 * @author gnaegi
 */
public class SimpleHTMLTagsFilter implements Filter {
	private static final OLog log = Tracing.createLoggerFor(SimpleHTMLTagsFilter.class);

	@Override
	public String filter(String original) {
		if(original == null) return null;
		if(original.isEmpty()) return "";
		
		try {
			SAXParser parser = new SAXParser();
			HTMLHandler contentHandler = new HTMLHandler(original.length());
			parser.setContentHandler(contentHandler);
			parser.parse(new InputSource(new StringReader(original)));
			String text = contentHandler.toString();
			text = text.replace('\u00a0', ' ');
			text = StringHelper.escapeHtml(text);
			return text;
		} catch (SAXException e) {
			log.error("", e);
			return null;
		} catch (IOException e) {
			log.error("", e);
			return null;
		} catch (Exception e) {
			log.error("", e);
			return null;
		}
	}
	
	private static class HTMLHandler extends DefaultHandler {
		private boolean collect = true;
		private boolean consumeBlanck = false;
		private final LimitedContentWriter content;
		
		public HTMLHandler(int size) {
			content = new LimitedContentWriter(size, FileDocumentFactory.getMaxFileSize());
		}

		@Override
		public void startElement(String uri, String localName, String qName, Attributes attributes) {
			String elem = localName.toLowerCase();
			if("script".equals(elem)) {
				collect = false;
			// add a single whitespace before each block element but only if not there is not already a whitespace there
			} else if("li".equals(elem)) {
				content.append(" ");
			} else if("br".equals(elem)) {
				content.append(" ");
			} else if(NekoHTMLFilter.blockTags.contains(elem) && content.length() > 0 && content.charAt(content.length() -1) != ' ' ) {
				consumeBlanck = true;
			}
		}
		
		@Override
		public void characters(char[] chars, int offset, int length) {
			if(collect) {
				if(consumeBlanck) {
					if(content.length() > 0 && content.charAt(content.length() -1) != ' ' && length > 0 && chars[offset] != ' ') { 
						content.append(' ');
					}
					consumeBlanck = false;
				}
				content.write(chars, offset, length);
			}
		}

		@Override
		public void endElement(String uri, String localName, String qName) {
			String elem = localName.toLowerCase();
			if("script".equals(elem)) {
				collect = true;
			} else if("li".equals(elem) || "p".equals(elem)) {
				content.append(" ");
			} else if(NekoHTMLFilter.blockTags.contains(elem) && content.length() > 0 && content.charAt(content.length() -1) != ' ' ) {
				consumeBlanck = true;
			}
		}
		
		@Override
		public String toString() {
			return content.toString();
		}
	}

}