How to convert PDF to HTML? Brief analysis of methods

With the advent of the digital age, more and more information is being digitized, of which PDF documents are the most common. Although PDF documents have great advantages in cross-platform and formatting standardization, they will encounter great difficulties in web page display and search activities. Therefore, converting PDF documents into HTML format has become a necessary task to make PDF documents easier to display and share on the Internet.

As a widely used programming language, Java provides many application program interfaces (APIs) for converting PDF to HTML. This article will introduce and compare the Java application program interfaces for converting PDF to HTML, and use Taking PDFBox, iText and Apache FOP as examples, we will explain in detail how to use these libraries to convert PDF to HTML.

1. The need to convert PDF to HTML

With the development of Internet culture, Web applications have become more and more an indispensable part of our lives, and converting PDF to HTML Format has obviously become a necessary requirement for Web applications. Here are the main requirements:

1. Searchability: PDF format files do not have the feature of text searchability, and using the PDF to HTML tool can convert the PDF content into HTML format. This will greatly improve text searchability.
2. Reprint and download: HTML is often used to share documents on the Web, so that others can view and download your documents at any time, and converting PDF to HTML format is more portable and easier to use.
3. Editability: For some PDF files that need to be edited, after converting them to HTML format, they can be easily edited using an HTML editor for convenient collaboration.

2. Comparison of PDF to HTML tools

PDF to HTML tools can be implemented based on the following three commonly used frameworks:

1. Apache PDFBox: is a Java-based library for processing PDF raw files. It can be used to extract text and graphic objects, translate some specific tags in PDF, insert and delete pages, etc.
2. iText: is an open source PDF library developed using Java. It can be used to extract or create new documents from existing PDF files. iText can also be used to generate advanced formats for PDF files.
3. Apache FOP: is an open source Java application for converting XML formatted data into PDF files. FOP can convert XSL-FO files to PDF files, supports Unicode and right-to-left text, inserts and moves pages, etc.

3. PDFBox

Apache PDFBox is an open source Java library for operating PDF files. In PDFBox, PDF is stored as plain text, PDFBox parses the PDF into memory and then renders it as plain text. Since PDFBox does not support complex formats and layouts, it is not suitable for processing large, complex PDF files. However, PDFBox supports export of fonts, colors, backgrounds, tables, and links, so converting PDF to HTML is easy.

Code example for PDFBox:

import java.io.IOException;
import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.text.PDFTextStripper;
public class PDFtoHTML {
    public static void main(String[] args) throws IOException {
        PDDocument document = null;
        try {
            document = PDDocument.load(file);
            PDFTextStripper stripper = new PDFTextStripper();
            String text = stripper.getText(document);
            System.out.println(text);
        } finally {
            if (document != null) {
                document.close();
            }
        }
    }
}

In this example code, the PDFTextStripper class is used to extract plain text from a PDF file. On this basis, you can also export PDF elements such as fonts, colors, backgrounds, tables, and links by adding other codes.

4. iText

iText is a free but commercial component Java PDF library that supports the creation, modification and extraction of various PDF files. iText has developed many PDF conversion tools, one of which is to convert PDF files to HTML.

To convert PDF files to HTML, you can use the HTMLWorker class and XMLWorker class provided by iText. The HTMLWorker class provides an HTMLWriter that can extract and convert text, paragraphs, lists, and other HTML elements from PDF documents. The XMLWorker class provides a more flexible way to support processing XML files, including HTML files.

Since iText can read text directly from PDF and save it to HTML file, the conversion process is very simple. However, it only has very good support for basic formatting and typesetting, and poor support for PDF files that are intricate and require complex operations.

Code example for iText:

import java.io.File;
import java.io.FileOutputStream;
import com.itextpdf.text.pdf.PdfReader;
import com.itextpdf.text.pdf.parser.PdfTextExtractor;
public class PDFtoHTML 
{
    public static void main( String[] args )
    {
        try {
            String inputurl="pdf/demo.pdf";
            String outputurl="html/demo.html";
            File file=new File(outputurl);
            if(!file.exists()){
                file.createNewFile();
            }
            PdfReader reader=new PdfReader(inputurl);
            int totalpages=reader.getNumberOfPages();
            StringBuffer buffer=new StringBuffer();
            for(int i=1;i<=totalpages;i++){
                buffer.append(PdfTextExtractor.getTextFromPage(reader,i));
            }
            FileOutputStream fos=new FileOutputStream(outputurl);
            fos.write(buffer.toString().getBytes());
            fos.flush();
            fos.close();
            reader.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

In this example code, the PdfReader class is used to extract text from a PDF file and then save the text directly to an HTML file.

5. Apache FOP

Apache FOP is a Java application for generating PDF files. It can convert XSL-FO files into PDF files. Apache FOP also provides the function of converting HTML files to PDF files as another option for converting PDF to HTML.

Since Apache FOP has good support for HTML and XML, when converting PDF to HTML, you can first convert it to XML and then use Apache FOP to convert it to HTML. Since XML is a simple, structured text format, it is very easy to use a Java parser to parse XML and convert it to HTML. However, using Apache FOP to process PDF to HTML often requires more complex configuration and installation to achieve ideal results.

Code example for Apache FOP:

import java.io.File;
import java.io.FileOutputStream;
import java.io.OutputStream;
import javax.xml.transform.Result;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.sax.SAXResult;
import javax.xml.transform.stream.StreamSource;
import org.apache.fop.apps.FOUserAgent;
import org.apache.fop.apps.Fop;
import org.apache.fop.apps.FopFactory;
import org.apache.fop.apps.MimeConstants;
 
public class PDFtoHTML {
    public static void main(String[] args) throws Exception {
        File xsltFile = new File("myXslt.xslt");
        File xmlFile = new File("myXml.xml");
        File htmlFile = new File("myHtml.html");
        FopFactory fopFactory = FopFactory.newInstance();
        FOUserAgent foUserAgent = fopFactory.newFOUserAgent();
        OutputStream out = new FileOutputStream(htmlFile);
        try {
            Fop fop = fopFactory.newFop(MimeConstants.MIME_HTML, foUserAgent, out);
            TransformerFactory factory = TransformerFactory.newInstance();
            Transformer transformer = factory.newTransformer(new StreamSource(xsltFile));
            Result res = new SAXResult(fop.getDefaultHandler());
            transformer.transform(new StreamSource(xmlFile), res);
        } finally {
            out.close();
        }
    }
}

In this example, FopFactory is used to open a Fop instance, convert the XML input to PDF, and then generate the HTML file. During the conversion process, you can also use an XSL stylesheet to control the HTML output.

6. Conclusion

This article introduces the main framework and related APIs for converting PDF to HTML using Java, including PDFBox, iText and Apache FOP. In practice, choosing a library that suits you requires comprehensive consideration based on your own needs. If you need to extract text individually, PDFBox may be more suitable; if you need to select and export different elements in a PDF, iText is the first choice; if you want to convert PDF to perfect HTML, Apache FOP is a more comprehensive solution.

In practice, if you need to perform more complex operations on PDFs, such as modifying layout, adding comments, or troubleshooting, you need to use more sophisticated tools and techniques, including Adobe Acrobat and fully customized PDF views. device. However, for most PDF to HTML conversion situations, it is very convenient to use the PDF to HTML conversion tool provided by the Java library.

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