Java to Find Unclosed HTML Tags

Question 1

I have Two Options for you (I like 2nd one the most.)

1. http://home.ccil.org/~cowan/XML/tagsoup

 instead of parsing well-formed or valid XML, 
 parses HTML as it is found in the wild: 
 poor, nasty and brutish, though quite often far from short.
 TagSoup is designed for
 people who have to process this stuff using 
 some semblance of a rational application   
 design. By providing a SAX interface, 
 it allows standard XML tools to be applied to even the
 worst HTML. TagSoup also includes a command-line processor that reads
 HTML files and can generate either clean HTML or well-formed XML 
 that is a close approximation to XHTML.

This the tool we are using. I mentioned another tool but im not using it.

2. http://htmlcleaner.sourceforge.net/download.php

Just download the jar file and unzip it. and Run the jar file like below.

Go to the Location
java -jar htmlcleaner-2.8.jar src=http://google.com It will correct missing tags and give output.

Eg - I have Html file with following contents

<table>
<tr>
<td>Wrong Table

it gives the out like below

C:\Users\Lasitha Benaragama\Downloads\htmlcleaner-2.8>java -jar htmlcleaner-2.8.
jar src=http://localhost/fun/test.html
Apr 24, 2014 12:23:10 PM org.htmlcleaner.audit.HtmlModificationListenerLogger fi
reHtmlError
INFO: fireHtmlError:RequiredParentMissing(true) at tr
Apr 24, 2014 12:23:10 PM org.htmlcleaner.audit.HtmlModificationListenerLogger fi
reHtmlError
INFO: fireHtmlError:UnclosedTag(true) at table
Apr 24, 2014 12:23:10 PM org.htmlcleaner.audit.HtmlModificationListenerLogger fi
reHtmlError
INFO: fireHtmlError:UnclosedTag(true) at tbody
Apr 24, 2014 12:23:10 PM org.htmlcleaner.audit.HtmlModificationListenerLogger fi
reHtmlError
INFO: fireHtmlError:UnclosedTag(true) at tr
Apr 24, 2014 12:23:10 PM org.htmlcleaner.audit.HtmlModificationListenerLogger fi
reHtmlError
INFO: fireHtmlError:UnclosedTag(true) at td
<?xml version="1.0" encoding="UTF-8"?>
<html>
<head />
<body><table>
<tbody><tr>
<td>Wrong Table</td></tr></tbody></table></body></html>

I tested your html also, The output is

C:\Users\Lasitha Benaragama\Downloads\htmlcleaner-2.8>java -jar htmlcleaner-2.8.
jar src=http://localhost/fun/test.html
<?xml version="1.0" encoding="UTF-8"?>
<html>
<head />
<body>

        <p style="margin-top: 0"> dasa </p>
        <input size="1" type="text" value="a" />

</body></html>
C:\Users\Lasitha Benaragama\Downloads\htmlcleaner-2.8>

Thanks.

Question 2

You could keep a stack of the tags. As you come across an open tag, push it onto the stack. When you come to a closing tag, pop off and make sure it matches the closing tag you are at. If it's not, that is a missing tag.

Question 3

Below code works perfectly for me:

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;

import org.ccil.cowan.tagsoup.Parser;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.io.SAXReader;
import org.dom4j.io.XMLWriter;
import org.xml.sax.SAXException;

public class EmailUtil {

    public static String getValidHtml(String html) throws SAXException, DocumentException, IOException {
        ByteArrayOutputStream baos = null;
        SAXReader reader = new SAXReader(Parser.class.getName());
        Document doc = reader.read(new ByteArrayInputStream(html.getBytes()));
        baos = new ByteArrayOutputStream();
        XMLWriter writer;
        writer = new XMLWriter(baos);
        writer.write(doc);
        return baos == null ? null : baos.toString();
    }
}