The open source JTidy project does an excellent job of converting HTML files to the newer XHTML standard. The following code shows how to invoke JTidy programmatically from Java:

/*In:  C:Data_Localxmldocs	est.htmlOut: C:Data_Localxmldocs	estXHTML.xml*/import org.w3c.tidy.Tidy;import java.io.FileInputStream;import java.io.FileOutputStream;import org.w3c.dom.Document;public class HTML_to_XHTML{   public static void main(String[] args){      try{         FileInputStream FIS=new FileInputStream("C://Data_Local            //xml//docs//test.html");         FileOutputStream FOS=new FileOutputStream("C://Data_Local            //xml//docs//testXHTML.xml");            Tidy T=new Tidy();         Document D=T.parseDOM(FIS,FOS);         }      catch (java.io.FileNotFoundException e)         {System.out.println(e.getMessage());}         }   }}