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High performace HTML parsing library [duplicate]

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Closed 11 years ago.
I'm working on an app which scrapes data from a website and I was wondering how I should go about getting the data. Specifically I need data contained in a number of div tags which use a specific CSS class - Currently (for testing purposes) I'm just checking for
div class = "classname"
in each line of HTML - This works, but I can't help but feel there is a better solution out there.
Is there any nice way where I could give a class a line of HTML and have some nice methods like:
boolean usesClass(String CSSClassname);
String getText();
String getLink();

Another library that might be useful for HTML processing is jsoup.
Jsoup tries to clean malformed HTML and allows html parsing in Java using jQuery like tag selector syntax.
http://jsoup.org/

The main problem as stated by preceding coments is malformed HTML, so an html cleaner or HTML-XML converter is a must. Once you get the XML code (XHTML) there are plenty of tools to handle it. You could get it with a simple SAX handler that extracts only the data you need or any tree-based method (DOM, JDOM, etc.) that let you even modify original code.
Here is a sample code that uses HTML cleaner to get all DIVs that use a certain class and print out all Text content inside it.
import java.io.IOException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import org.htmlcleaner.HtmlCleaner;
import org.htmlcleaner.TagNode;
/**
* #author Fernando Miguélez Palomo <fernandoDOTmiguelezATgmailDOTcom>
*/
public class TestHtmlParse
{
static final String className = "tags";
static final String url = "http://www.stackoverflow.com";
TagNode rootNode;
public TestHtmlParse(URL htmlPage) throws IOException
{
HtmlCleaner cleaner = new HtmlCleaner();
rootNode = cleaner.clean(htmlPage);
}
List getDivsByClass(String CSSClassname)
{
List divList = new ArrayList();
TagNode divElements[] = rootNode.getElementsByName("div", true);
for (int i = 0; divElements != null && i < divElements.length; i++)
{
String classType = divElements[i].getAttributeByName("class");
if (classType != null && classType.equals(CSSClassname))
{
divList.add(divElements[i]);
}
}
return divList;
}
public static void main(String[] args)
{
try
{
TestHtmlParse thp = new TestHtmlParse(new URL(url));
List divs = thp.getDivsByClass(className);
System.out.println("*** Text of DIVs with class '"+className+"' at '"+url+"' ***");
for (Iterator iterator = divs.iterator(); iterator.hasNext();)
{
TagNode divElement = (TagNode) iterator.next();
System.out.println("Text child nodes of DIV: " + divElement.getText().toString());
}
}
catch(Exception e)
{
e.printStackTrace();
}
}
}

Several years ago I used JTidy for the same purpose:
http://jtidy.sourceforge.net/
"JTidy is a Java port of HTML Tidy, a HTML syntax checker and pretty printer. Like its non-Java cousin, JTidy can be used as a tool for cleaning up malformed and faulty HTML. In addition, JTidy provides a DOM interface to the document that is being processed, which effectively makes you able to use JTidy as a DOM parser for real-world HTML.
JTidy was written by Andy Quick, who later stepped down from the maintainer position. Now JTidy is maintained by a group of volunteers.
More information on JTidy can be found on the JTidy SourceForge project page ."

You might be interested by TagSoup, a Java HTML parser able to handle malformed HTML. XML parsers would work only on well formed XHTML.

The HTMLParser project (http://htmlparser.sourceforge.net/) might be a possibility. It seems to be pretty decent at handling malformed HTML. The following snippet should do what you need:
Parser parser = new Parser(htmlInput);
CssSelectorNodeFilter cssFilter =
new CssSelectorNodeFilter("DIV.targetClassName");
NodeList nodes = parser.parse(cssFilter);

Jericho: http://jericho.htmlparser.net/docs/index.html
Easy to use, supports not well formed HTML, a lot of examples.

HTMLUnit might be of help. It does a lot more stuff too.
http://htmlunit.sourceforge.net/1

Let's not forget Jerry, its jQuery in java: a fast and concise Java Library that simplifies HTML document parsing, traversing and manipulating; includes usage of css3 selectors.
Example:
Jerry doc = jerry(html);
doc.$("div#jodd p.neat").css("color", "red").addClass("ohmy");
Example:
doc.form("#myform", new JerryFormHandler() {
public void onForm(Jerry form, Map<String, String[]> parameters) {
// process form and parameters
}
});
Of course, these are just some quick examples to get the feeling how it all looks like.

The nu.validator project is an excellent, high performance HTML parser that doesn't cut corners correctness-wise.
The Validator.nu HTML Parser is an implementation of the HTML5 parsing algorithm in Java. The parser is designed to work as a drop-in replacement for the XML parser in applications that already support XHTML 1.x content with an XML parser and use SAX, DOM or XOM to interface with the parser. Low-level functionality is provided for applications that wish to perform their own IO and support document.write() with scripting. The parser core compiles on Google Web Toolkit and can be automatically translated into C++. (The C++ translation capability is currently used for porting the parser for use in Gecko.)

You can also use XWiki HTML Cleaner:
It uses HTMLCleaner and extends it to generate valid XHTML 1.1 content.

If your HTML is well-formed, you can easily employ an XML parser to do the job for you... If you're only reading, SAX would be ideal.

Some help scraping a page in Java

I need to scrape a web page using Java and I've read that regex is a pretty inefficient way of doing it and one should put it into a DOM Document to navigate it.
I've tried reading the documentation but it seems too extensive and I don't know where to begin.
Could you show me how to scrape this table in to an array? I can try figuring out my way from there. A snippet/example would do just fine too.
Thanks.

You can try jsoup: Java HTML Parser. It is an excellent library with good sample codes.

Transform the web page you are trying to scrap into an XHTML document. There are several options to do this with Java, such as JTidy and HTMLCleaner. These tools will also automatically fix malformed HTML (e.g., close unclosed tags). Both work very well, but I prefer JTidy because it integrates better with Java's DOM API;
Extract required information using XPath expressions.
Here is a working example using JTidy and the Web Page you provided, used to extract all file names from the table.
public static void main(String[] args) throws Exception {
// Create a new JTidy instance and set options
Tidy tidy = new Tidy();
tidy.setXHTML(true);
// Parse an HTML page into a DOM document
URL url = new URL("http://www.cs.grinnell.edu/~walker/fluency-book/labs/sample-table.html");
Document doc = tidy.parseDOM(url.openStream(), System.out);
// Use XPath to obtain whatever you want from the (X)HTML
XPath xpath = XPathFactory.newInstance().newXPath();
XPathExpression expr = xpath.compile("//td[#valign = 'top']/a/text()");
NodeList nodes = (NodeList)expr.evaluate(doc, XPathConstants.NODESET);
List<String> filenames = new ArrayList<String>();
for (int i = 0; i < nodes.getLength(); i++) {
filenames.add(nodes.item(i).getNodeValue());
}
System.out.println(filenames);
}
The result will be [Integer Processing:, Image Processing:, A Photo Album:, Run-time Experiments:, More Run-time Experiments:] as expected.
Another cool tool that you can use is Web Harvest. It basically does everything I did above but using an XML file to configure the extraction pipeline.

Regex is definitely the way to go. Building a DOM is overly complicated and itself requires a lot of text parsing.

If all you are doing is scraping a table into a datafile, regex will be just fine, and may be even better than using a DOM document. DOM documents will use up a lot of memory (especially for really large data tables) so you probably want a SAX parser for large documents.

How to use HTML Parser to get complete information about all tags in the HTML page

I am using HTML Parser to develop an application.
The code below is not able to get the entire set of tags in the page.
There are some tags which are missed out and the attributes and text body of them are also missed out.
Please help me to explain why is this happening.....or suggest me other way....
URL url = new URL("...");
PrintWriter pw=new PrintWriter(new FileWriter("HTMLElements.txt"));
URLConnection connection = url.openConnection();
InputStream is = connection.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
HTMLEditorKit htmlKit = new HTMLEditorKit();
HTMLDocument htmlDoc = (HTMLDocument)htmlKit.createDefaultDocument();
HTMLEditorKit.Parser parser = new ParserDelegator();
HTMLEditorKit.ParserCallback callback = htmlDoc.getReader(0);
parser.parse(br, callback, true);
ElementIterator iterator = new ElementIterator(htmlDoc);
Element element;
while ((element = iterator.next()) != null)
{
AttributeSet attributes = element.getAttributes();
Enumeration e=attributes.getAttributeNames();
pw.println("Element Name :"+element.getName());
while(e.hasMoreElements())
{
Object key=e.nextElement();
Object val=attributes.getAttribute(key);
int startOffset = element.getStartOffset();
int endOffset = element.getEndOffset();
int length = endOffset - startOffset;
String text=htmlDoc.getText(startOffset, length);
pw.println("Key :"+key.toString()+" Value :"+val.toString()+"\r\n"+"Text :"+text+"\r\n");
}
}
}

I am doing this fairly reliably with HTML Parser, (provided that the HTML document does not change its structure). A web service with a stable API is much better, but sometimes we just do not have one.
General idea:
You first have to know in what tags (div, meta, span, etc) the information you want are in, and know the attributes to identify those tags. Example :
<span class="price"> $7.95</span>
if you are looking for this "price", then you are interested in span tags with class "price".
HTML Parser has a filter-by-attribute functionality.
filter = new HasAttributeFilter("class", "price");
When you parse using a filter, you will get a list of Nodes that you can do a instanceof operation on them to determine if they are of the type you are interested in, for span you'd do something like
if (node instanceof Span) // or any other supported element.
See list of supported tags here.
An example with HTML Parser to grab the meta tag that has description about a site:
Tag Sample :
<meta name="description" content="Amazon.com: frankenstein: Books"/>
Code:
import org.htmlparser.Node;
import org.htmlparser.Parser;
import org.htmlparser.util.NodeList;
import org.htmlparser.util.ParserException;
import org.htmlparser.filters.HasAttributeFilter;
import org.htmlparser.tags.MetaTag;
public class HTMLParserTest {
public static void main(String... args) {
Parser parser = new Parser();
//<meta name="description" content="Some texte about the site." />
HasAttributeFilter filter = new HasAttributeFilter("name", "description");
try {
parser.setResource("http://www.youtube.com");
NodeList list = parser.parse(filter);
Node node = list.elementAt(0);
if (node instanceof MetaTag) {
MetaTag meta = (MetaTag) node;
String description = meta.getAttribute("content");
System.out.println(description);
// Prints: "YouTube is a place to discover, watch, upload and share videos."
}
} catch (ParserException e) {
e.printStackTrace();
}
}
}

As per the comments:
actually i want to extract information such as product name,price etc of all products listed in an online shopping site such as amazon.com How should i go about it???
Step 1: read their robots file. It's usually found on the root of the site, for example http://amazon.com/robots.txt. If the URL you're trying to access is covered by a Disallow on an User-Agent of *, then stop here. Contact them, explain them in detail what you're trying to do and ask them for ways/alternatives/webservices which can provide you the information you need. Else you're violating the laws and you may risk to get blacklisted by the site and/or by your ISP or worse. If not, then proceed to step 2.
Step 2: check if the site in question hasn't already a public webservice available which is much more easy to use than parsing a whole HTML page. Using a webservice, you'll get exactly the information you're looking for in a concise format (JSON or XML) based on a simple set of parameters. Look around or contact them for details about any webservices. If there's no way, proceed to step 3.
Step 3: learn how HTML/CSS/JS work, learn how to work with webdeveloper tools like Firebug, learn how to interpret the HTML/CSS/JS source you see by rightclick > View Page Source. My bet that the site in question uses JS/Ajax to load/populate the information you'd like to gather. In that case, you'll need to use a HTML parser which is capable of parsing and executing JS as well (the one you're using namely doesn't do that). This isn't going to be an easy job, so I won't explain it in detail until it's entirely clear what you're trying to achieve and if that is allowed and if there aren't more-easy-to-use webservices available.

You seemed to use the Swing HtmlDocument. It may not be the smartest idea ever.
I believe you would have better results using, as an example, NekoHtml.

Or another simple library you can use is jtidy that can clean up your html before parsing it.
Hope this helps.
http://sourceforge.net/projects/jtidy/
Ciao!

Libs for HTML sanitizing

I'm looking for a html sanitizer which I can call per API to sanitise strings which I get from my webapp. Are there some useful easy to use libs available? Does anyone knows maybe one or two?
I don't need something big it just must be able to find unclosed tags and close them.

https://github.com/OWASP/java-html-sanitizer is now marked ready for production use.
A fast and easy to configure HTML Sanitizer written in Java which lets you include HTML authored by third-parties in your web application while protecting against XSS.
You can use prepackaged policies
Sanitizers.FORMATTING.and(Sanitizers.LINKS)
or the tests show how you can configure your own easily:
new HtmlPolicyBuilder()
.allowElements("a")
.allowUrlProtocols("https")
.allowAttributes("href").onElements("a")
.requireRelNofollowOnLinks()
or write custom policies to do things like changing h1s to divs with a certain class:
new HtmlPolicyBuilder()
.allowElements("h1", "p")
.allowElements(
new ElementPolicy() {
public String apply(String elementName, List<String> attrs) {
attrs.add("class");
attrs.add("header-" + elementName);
return "div";
}
}, "h1"))

JTidy may help you.

The HTML Parser JSoup also supports sanitisation by policy: http://jsoup.org/cookbook/cleaning-html/whitelist-sanitizer

Apart from JTidy you can also take a look at:
Nekohtml
TagSoup
Getting text in HTmL document

http://roberto.open-lab.com/2009/11/05/a-java-html-sanitizer-also-against-xss/

Best method to parse various custom XML documents in Java

What is the best method to parse multiple, discrete, custom XML documents with Java?

I would use Stax to parse XML, it's fast and easy to use. I've been using it on my last project to parse XML files up to 24MB. There's a nice introduction on java.net, which tells you everything you need to know to get started.

Basically, you have two main XML parsing methods in Java :
SAX, where you use an handler to only grab what you want in your XML and ditch the rest
DOM, which parses your file all along, and allows you to grab all elements in a more tree-like fashion.
Another very useful XML parsing method, albeit a little more recent than these ones, and included in the JRE only since Java6, is StAX. StAX was conceived as a medial method between the tree-based of DOM and event-based approach of SAX. It is quite similar to SAX in the fact that parsing very large documents is easy, but in this case the application "pulls" info from the parser, instead of the parsing "pushing" events to the application. You can find more explanation on this subject here.
So, depending on what you want to achieve, you can use one of these approaches.

Use the dom4j library
First read the document
import java.net.URL;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.io.SAXReader;
public class Foo {
public Document parse(URL url) throws DocumentException {
SAXReader reader = new SAXReader();
Document document = reader.read(url);
return document;
}
}
Then use XPATH to get to the values you need
public void get_author(Document document) {
Node node = document.selectSingleNode( "//AppealRequestProcessRequest/author" );
String author = node.getText();
return author;
}

You will want to use org.xml.sax.XMLReader (http://docs.oracle.com/javase/7/docs/api/org/xml/sax/XMLReader.html).

If you only need to parse then I would recommend using XPath library. Here is a nice reference: http://www.ibm.com/developerworks/library/x-javaxpathapi.html
But you may want to consider turning XMLs to objects and then the sky is the limit.
For that you may use XStream, this is a great library which i use alot

Below is the code of extracting some value value using vtd-xml.
import com.ximpleware.*;
public class extractValue{
public static void main(String s[]) throws VTDException, IOException{
VTDGen vg = new VTDGen();
if (!vg.parseFile("input.xml", false));
VTDNav vn = vg.getNav();
AutoPilot ap = new AutoPilot(vn);
ap.selectXPath("/aa/bb[name='k1']/value");
int i=0;
while ((i=ap.evalXPath())!=-1){
System.out.println(" value ===>"+vn.toString(i));
}
}
}