Converting HTML pages to PDF in pure Java

There are plenty of commercial HTML to PDF converters for the .NET platform (most of which are based on the Internet Explorer libraries that are available in Windows), but HTML to PDF conversion in Java is not that easy. But not impossible. FlyingSaucer allows to convert properly formatted XHTML and CSS2 to PDF (which is in details described here: http://today.java.net/pub/a/today/2007/06/26/generating-pdfs-with-flying-saucer-and-itext.html). However, unfortunately most of the web pages out there are not designed in XHTML. FlyingSuacer when it has to deal with such pages would simply throw an exception and quit. But there also a solution to this limitation, as the developers of FlyingSaucer suggest, we could use one of the existing HTML code cleaners (for example TagSoup, JTidy or HTMLCleaner) for that purpose. Below I would like to show you an example of using HTMLCleaner, FlyingSaucer and iText to convert the HTML to PDF.

package htmltopdf;

import com.lowagie.text.DocumentException;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URL;
import java.util.logging.Level;
import java.util.logging.Logger;
import org.apache.commons.io.IOUtils;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.htmlcleaner.CleanerProperties;
import org.htmlcleaner.CommentNode;
import org.htmlcleaner.HtmlCleaner;
import org.htmlcleaner.HtmlNode;
import org.htmlcleaner.PrettyXmlSerializer;
import org.htmlcleaner.TagNode;
import org.htmlcleaner.TagNodeVisitor;
import org.htmlcleaner.Utils;
import org.xhtmlrenderer.pdf.ITextRenderer;


public class HTMLtoPDF {

    static int cssCounter = 0;
    
    public static void main(String[] args) {
        try {
            final String site = "http://www.keysurvey.co.za";
            final String page = "/company/";
            final String cssUrl = "http://www.keysurvey.co.za";
            
            URL url = new URL(site+page);

            CleanerProperties props = new CleanerProperties();

// HTMLCleaner part
// set some properties to non-default values
            props.setTranslateSpecialEntities(true);
            props.setTransResCharsToNCR(true);
            props.setOmitComments(true);

// do parsing
            TagNode tagNode = new HtmlCleaner(props).clean(url);
            tagNode.traverse(new TagNodeVisitor() {

                public boolean visit(TagNode tagNode, HtmlNode htmlNode) {
                    if (htmlNode instanceof TagNode) {
                        TagNode tag = (TagNode) htmlNode;
                        String tagName = tag.getName();
                        if ("img".equals(tagName)) {
                            String src = tag.getAttributeByName("src");
                            if (src != null && ! src.startsWith("http")) {
                                tag.setAttribute("src", Utils.fullUrl(site, src));
                            }
                        }
                        if ("link".equals(tagName)) {
                            String rel = tag.getAttributeByName("rel");
                            String href = tag.getAttributeByName("href");
                            if (href != null && "stylesheet".equals(rel)) {
                                try {
                                    HttpClient client = new DefaultHttpClient();
                                    String fullUrl = "";
                                    if (href.startsWith("http")) fullUrl = href;
                                    else fullUrl = Utils.fullUrl(cssUrl, href);
                                    HttpGet get = new HttpGet(fullUrl);
                                    HttpResponse response = client.execute(get);
                                    HttpEntity entity = response.getEntity();
                                    if (entity != null) {
                                        InputStream is = entity.getContent();
                                        href = "css" + cssCounter + ".css";
                                        cssCounter++;
                                        OutputStream os = new FileOutputStream(href);
                                        IOUtils.copy(is, os);
                                    }
                                    tag.setAttribute("href", href);
                                } catch (IOException ex) {
                                    Logger.getLogger(HTMLtoPDF.class.getName()).log(Level.SEVERE, null, ex);
                                }
                            }
                        }
                    } else if (htmlNode instanceof CommentNode) {
                        CommentNode comment = ((CommentNode) htmlNode);
                        comment.getContent().append(" -- By HtmlCleaner");
                    }
                    // tells visitor to continue traversing the DOM tree
                    return true;
                }
            });



// serialize to xml file
            new PrettyXmlSerializer(props).writeToFile(
                    tagNode, "page.xhtml", "utf-8");

// FlyingSaucer and iText part
            String inputFile = "page.xhtml";
            String url2 = new File(inputFile).toURI().toURL().toString();
            String outputFile = "firstdoc.pdf";
            OutputStream os = new FileOutputStream(outputFile);

            ITextRenderer renderer = new ITextRenderer();
            renderer.setDocument(url2);
            renderer.layout();
            renderer.createPDF(os);

            os.close();


        } catch (DocumentException ex) {
            Logger.getLogger(HTMLtoPDF.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IOException ex) {
            Logger.getLogger(HTMLtoPDF.class.getName()).log(Level.SEVERE, null, ex);

        }
    }
}

FlyingSaucer cannot read the CSS files over the web, so we have to save them locally. While parsing the HTML source of the page, for all of the link tags with rel='stylesheet', we need to save a local copy of the css file. Also relative links to the image files need to be replaced with the absolute URLs.

To compile and run the above example you will need the Jars supplied with the FlyingSaucer distribution (it includes XHTMLRenderer and iText), Apache HttpClient, Apache IOUtils and HTMLCleaner.

Overall the code works fairly well on various even poorly formatted pages. There are a few issues that I have noted that may prevent some pages from being rendered to PDF correctly. Here are some of them:
1. Some types of comments (i.e. .ClassName /* some comment */ { ... } ) are not supported by the CSS parser of FlyingSaucer . It simply stops parsing CSS without throwing any exceptions.
2. @import and url() properties of the CSS are not supported.

But overall for many pages the described solution should be goo enough, especially when you need to convert internal pages that you can properly prepare for the PDF conversion.