Recently, I needed to build a component, that given a URL, would try to extract the summary of the page from it. One of the first things I do when I need to build something about which I don't know much is to check out if there are other people who have built similar things, and have been kind enough to post their code or created a project that I can reuse. While lot of people may consider this mildly unethical, I think it is a good practice because you get to know what's available, and go down paths that have the highest probability of success (based on the theory that if something didn't work out, people won't post articles and blogs about it). I also credit my sources in my code, as well as post code (admittedly of dubious value) myself in the hope it may help someone else.
One of the first results for 'Web Page Summarizer' from Google is Aaron Weiss's article from the Web Developer's Virtual Library (WDVL). Its written in Perl and depends on modules developed earlier in the series.
I work mostly in Java, and I needed to use Java to do the same thing. I have been looking at using the Jericho HTML Parser, and this appeared to be quite a good use case. In this post, I replicate the functionality of Aaron Weiss's Web Page Summarizer in Java. Here is the code:
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93 | // WebPageSummarizer.java
package com.mycompany.myapp.utils;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.apache.commons.httpclient.NameValuePair;
import au.id.jericho.lib.html.CharacterReference;
import au.id.jericho.lib.html.Element;
import au.id.jericho.lib.html.HTMLElementName;
import au.id.jericho.lib.html.Source;
import au.id.jericho.lib.html.StartTag;
public class WebPageSummarizer {
/**
* Return a Map of extracted attributes from the web page identified by url.
* @param url the url of the web page to summarize.
* @return a Map of extracted attributes and their values.
*/
public Map<String,Object> summarize(String url) throws Exception {
Map<String,Object> summary = new HashMap<String,Object>();
Source source = new Source(new URL(url));
source.fullSequentialParse();
summary.put("title", getTitle(source));
summary.put("description", getMetaValue(source, "description"));
summary.put("keywords", getMetaValue(source, "keywords"));
summary.put("images", getElementText(source, HTMLElementName.IMG, "src", "alt"));
summary.put("links", getElementText(source, HTMLElementName.A, "href"));
return summary;
}
public String getTitle(Source source) {
Element titleElement=source.findNextElement(0, HTMLElementName.TITLE);
if (titleElement == null) {
return null;
}
// TITLE element never contains other tags so just decode it collapsing whitespace:
return CharacterReference.decodeCollapseWhiteSpace(titleElement.getContent());
}
private String getMetaValue(Source source, String key) {
for (int pos = 0; pos < source.length(); ) {
StartTag startTag = source.findNextStartTag(pos, "name", key, false);
if (startTag == null) {
return null;
}
if (startTag.getName() == HTMLElementName.META) {
String metaValue = startTag.getAttributeValue("content");
if (metaValue != null) {
metaValue = LcppStringUtils.removeLineBreaks(metaValue);
}
return metaValue;
}
pos = startTag.getEnd();
}
return null;
}
private List<NameValuePair> getElementText(Source source, String tagName,
String urlAttribute) {
return getElementText(source, tagName, urlAttribute, null);
}
@SuppressWarnings("unchecked")
private List<NameValuePair> getElementText(Source source, String tagName,
String urlAttribute, String srcAttribute) {
List<NameValuePair> pairs = new ArrayList<NameValuePair>();
List<Element> elements = source.findAllElements(tagName);
for (Element element : elements) {
String url = element.getAttributeValue(urlAttribute);
if (url == null) {
continue;
}
// A element can contain other tags so need to extract the text from it:
String label = element.getContent().getTextExtractor().toString();
if (label == null) {
// if text content is not available, get info from the srcAttribute
label = element.getAttributeValue(srcAttribute);
}
// if still null, replace label with the url
if (label == null) {
label = url;
}
pairs.add(new NameValuePair(label, url));
}
return pairs;
}
}
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As you can see, its all quite simple. Probably too simple, since there is a lot more I need to do to make this robust enough for general use. If you look at the Jericho site, you will find examples that describe all that I have done above, as well as some other things. However, using Jericho makes it easy to extend the code to cover corner cases, as I no longer have to rely on messy regular expression matching strategies (which I had used till now to parse HTML).
Here is the test case that hits the page that is the inspiration for this summarizer.
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43 | // WebPageSummarizerTest.java
package com.mycompany.myapp.utils;
import java.util.List;
import java.util.Map;
import org.apache.commons.httpclient.NameValuePair;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.junit.Test;
public class WebPageSummarizerTest {
private final Log log = LogFactory.getLog(getClass());
private static final String[] TEST_URLS = {
"http://www.wdvl.com/Authoring/Languages/Perl/PerlfortheWeb/summarizer.html",
};
@Test
public void testGetSummary() throws Exception {
WebPageSummarizer summarizer = new WebPageSummarizer();
for (String testUrl : TEST_URLS) {
System.out.println("==\nSummary for url:" + testUrl);
Map<String,Object> summaryMap = summarizer.summarize(testUrl);
for (String tag : summaryMap.keySet()) {
Object value = summaryMap.get(tag);
if (value == null) {
continue;
}
if (value instanceof String) {
System.out.println(tag + " => " + summaryMap.get(tag));
} else if (value instanceof List) {
List<NameValuePair> pairs = (List<NameValuePair>) value;
System.out.println("#-" + tag + " => " + pairs.size());
} else {
log.warn("Unknown value of class:" + value.getClass().getName());
continue;
}
}
}
}
}
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and the output:
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8 | Summary for url: http://www.wdvl.com/Authoring/Languages/Perl/PerlfortheWeb/summarizer.html
#-images => 58
title => WDVL: The Proof is in the Parsing: A Web Page Summarizer
keywords => Perl, PERL, programming, scripting, CGI, LWP, TokeParser
description => The Web Developer's Virtual Library is a resource for web development, including
a JavaScript tutorial, html tag info, JavaScript events, html special characters, paint shop pro,
database normalization, PHP and more.
#-links => 246
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On a slightly different note, I notice that I have been indulging in a bad practice - that of running my large batch programs using a JUnit test. I recently had a new developer start some of these tests inadvertently and start to wonder what the tests were doing after they cleaned up quite a few database tables :-). In the Ant world, I would use the java target to run my classes using a main() method, but its only recently I found out about the Maven2 exec plugin, so I will look at using that instead for my batch programs.
