Of course! Converting a DOCX file to HTML in Java is a common requirement for web applications, document processing, or content management systems. Here’s a comprehensive guide covering the most popular and robust libraries, with complete code examples.

Summary of Options

Method 1: Using Apache POI (Recommended & Powerful)

Apache POI is the go-to library for all things Microsoft Office in Java. While it's not a dedicated DOCX-to-HTML converter, its XWPF package has a built-in converter that is surprisingly good for most use cases.

Step 1: Add Dependencies

You'll need the Apache POI core library and the OOXML (Office Open XML) support.

If you're using Maven, add this to your pom.xml:

<dependencies>
    <!-- Apache POI Core -->
    <dependency>
        <groupId>org.apache.poi</groupId>
        <artifactId>poi</artifactId>
        <version>5.2.4</version>
    </dependency>
    <!-- Apache POI for Office Open XML formats (like .docx) -->
    <dependency>
        <groupId>org.apache.poi</groupId>
        <artifactId>poi-ooxml</artifactId>
        <version>5.2.4</version>
    </dependency>
</dependencies>

If you're using Gradle, add this to your build.gradle:

implementation 'org.apache.poi:poi:5.2.4'
implementation 'org.apache.poi:poi-ooxml:5.2.4'

Step 2: Write the Java Code

The XWPFDocument class has a convenient method getAllPictures() to handle images and a method to write the document to an OutputStream as HTML.

Here is a complete, runnable example:

import org.apache.poi.xwpf.converter.core.XWPFConverterException;
import org.apache.poi.xwpf.converter.html.XHTMLConverter;
import org.apache.poi.xwpf.converter.html.XHTMLOptions;
import org.apache.poi.xwpf.usermodel.XWPFDocument;
import org.apache.poi.xwpf.usermodel.XWPFParagraph;
import org.apache.poi.xwpf.usermodel.XWPFRun;
import org.apache.poi.xwpf.usermodel.XWPFTable;
import org.apache.poi.xwpf.usermodel.XWPFTableCell;
import org.apache.poi.xwpf.usermodel.XWPFTableRow;
import java.io.*;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.List;
public class DocxToHtmlConverter {
    public static void main(String[] args) {
        // 1. Define input and output paths
        Path docxPath = Paths.get("input.docx");
        Path htmlPath = Paths.get("output.html");
        Path imageDir = Paths.get("images");
        try {
            // 2. Create directories if they don't exist
            if (!Files.exists(imageDir)) {
                Files.createDirectories(imageDir);
            }
            // 3. Load the DOCX file
            try (InputStream docxInputStream = Files.newInputStream(docxPath);
                 XWPFDocument document = new XWPFDocument(docxInputStream)) {
                // 4. Configure HTML conversion options
                XHTMLOptions options = XHTMLOptions.create();
                // Set a directory to save images extracted from the DOCX
                options.setIgnoreIfMissingPicture(true);
                options.setExtractImageToFolder(imageDir.toFile());
                // 5. Perform the conversion
                try (OutputStream htmlOutputStream = Files.newOutputStream(htmlPath)) {
                    XHTMLConverter.getInstance().convert(document, htmlOutputStream, options);
                }
                System.out.println("Conversion successful! HTML saved to: " + htmlPath);
                System.out.println("Images saved to: " + imageDir);
            } catch (XWPFConverterException e) {
                System.err.println("Error during DOCX to HTML conversion: " + e.getMessage());
            }
        } catch (IOException e) {
            System.err.println("Error reading DOCX file or writing HTML file: " + e.getMessage());
        }
    }
}

Explanation:

1. Paths: We define the path for the input .docx file and the output .html file. We also create a directory (images) to store any images embedded in the document.
2. Load Document: new XWPFDocument(docxInputStream) loads the DOCX file into memory.
3. XHTMLOptions: This class is crucial for customizing the conversion.
   • XHTMLOptions.create() creates a default set of options.
   • options.setExtractImageToFolder(imageDir.toFile()) tells POI to extract all images from the DOCX and save them into the specified directory. The HTML will then reference these images using relative paths (e.g., images/image1.png).
4. XHTMLConverter: This is the core class that performs the conversion. Its convert method takes the XWPFDocument, the output stream for the HTML, and the options.

Method 2: Using docx4j (Excellent Alternative)

docx4j is another powerful library, often praised for its high-fidelity conversion, especially with complex documents. It also handles headers, footers, and other document parts very well.

Step 1: Add Dependencies

Maven (pom.xml):

<dependencies>
    <!-- docx4j Core Library -->
    <dependency>
        <groupId>org.docx4j</groupId>
        <artifactId>docx4j-core</artifactId>
        <version>11.4.4</version>
    </dependency>
    <!-- docx4j Exporter for HTML -->
    <dependency>
        <groupId>org.docx4j</groupId>
        <artifactId>docx4j-export-fo</artifactId>
        <version>11.4.4</version>
    </dependency>
    <!-- For SVG support, sometimes needed for complex shapes -->
    <dependency>
        <groupId>org.apache.xmlgraphics</groupId>
        <artifactId>batik-all</artifactId>
        <version>1.14</version>
        <type>pom</type>
    </dependency>
</dependencies>

Step 2: Write the Java Code

docx4j's conversion process involves transforming the DOCX into an intermediate format (XSL-FO) and then converting that to HTML.

import org.docx4j.Docx4J;
import org.docx4j.openpackaging.packages.WordprocessingMLPackage;
import org.docx4j.openpackaging.parts.WordprocessingML.MainDocumentPart;
import java.io.File;
import java.io.FileOutputStream;
import java.io.OutputStream;
public class Docx4jConverter {
    public static void main(String[] args) {
        // 1. Define input and output paths
        String docxPath = "input.docx";
        String htmlPath = "output_docx4j.html";
        String imageDir = "images_docx4j";
        // Create image directory
        new File(imageDir).mkdirs();
        try {
            // 2. Load the DOCX package
            WordprocessingMLPackage wordMLPackage = WordprocessingMLPackage.load(new File(docxPath));
            // 3. Configure conversion options
            // You can set options here, like image handling.
            // Docx4j handles image extraction automatically.
            Docx4J.setHyperlinkStyle("Hyperlink"); // Optional: set a style for hyperlinks
            // 4. Perform the conversion
            // Docx4j converts DOCX -> XSL-FO -> HTML
            OutputStream htmlOutputStream = new FileOutputStream(htmlPath);
            Docx4J.convert(wordMLPackage, htmlOutputStream, Docx4J.HTML);
            System.out.println("Conversion successful! HTML saved to: " + htmlPath);
            System.out.println("Images should be in a sub-folder of the document's location.");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Explanation:

1. Load Package: WordprocessingMLPackage.load() is the entry point for docx4j.
2. Docx4J.convert(): This is the main method. It's smart enough to know you want HTML. It will:
   • Extract images and save them in a folder named _rels or similar, relative to your output HTML file.
   • Convert the document content, preserving styles, tables, and lists.
   • The conversion is very accurate but can produce more complex HTML than Apache POI.

Method 3: The Two-Step Process (POI + jsoup)

Sometimes, the HTML generated by POI or docx4j is good but not perfectly clean. You might want to remove unnecessary <span> tags, fix attributes, or simplify the structure. This is where jsoup shines.

Step 1: Add jsoup Dependency

Maven (pom.xml):

<dependency>
    <groupId>org.jsoup</groupId>
    <artifactId>jsoup</artifactId>
    <version>1.15.4</version>
</dependency>

Step 2: Write the Java Code

This example first converts the DOCX to HTML using Apache POI, then cleans it up using jsoup.

import org.apache.poi.xwpf.converter.core.XWPFConverterException;
import org.apache.poi.xwpf.converter.html.XHTMLConverter;
import org.apache.poi.xwpf.converter.html.XHTMLOptions;
import org.apache.poi.xwpf.usermodel.XWPFDocument;
import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;
import org.jsoup.safety.Safelist;
import java.io.*;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
public class DocxToHtmlWithJsoup {
    public static void main(String[] args) {
        Path docxPath = Paths.get("input.docx");
        Path rawHtmlPath = Paths.get("raw_output.html");
        Path cleanHtmlPath = Paths.get("clean_output.html");
        try {
            // Step 1: Convert DOCX to HTML using Apache POI
            try (InputStream docxInputStream = Files.newInputStream(docxPath);
                 XWPFDocument document = new XWPFDocument(docxInputStream);
                 OutputStream htmlOutputStream = Files.newOutputStream(rawHtmlPath)) {
                XHTMLOptions options = XHTMLOptions.create();
                XHTMLConverter.getInstance().convert(document, htmlOutputStream, options);
            }
            System.out.println("Raw HTML generated by POI.");
            // Step 2: Clean the HTML using jsoup
            String rawHtml = new String(Files.readAllBytes(rawHtmlPath));
            // Safelist allows only specific tags and attributes.
            // This is a good starting point to remove inline styles and other clutter.
            Safelist cleanList = Safelist.relaxed()
                    .addTags("p", "h1", "h2", "h3", "h4", "h5", "h6", "ul", "ol", "li", 
                             "strong", "em", "u", "br", "hr", "a", "img", "table", "thead", 
                             "tbody", "tr", "th", "td", "div", "span");
            // Jsoup's .clean() method sanitizes the HTML based on the safelist.
            // For cleaning instead of sanitizing, you can use Jsoup's other methods like .select().
            // A more common approach is to remove unwanted elements:
            Document doc = Jsoup.parse(rawHtml);
            // Remove all <span> tags, keeping their content
            doc.select("span").unwrap();
            // Remove all style attributes
            doc.select("style").remove();
            doc.select("[style]").removeAttr("style");
            String cleanHtml = doc.html();
            // Save the cleaned HTML
            Files.write(cleanHtmlPath, cleanHtml.getBytes());
            System.out.println("HTML cleaned and saved to: " + cleanHtmlPath);
        } catch (IOException | XWPFConverterException e) {
            e.printStackTrace();
        }
    }
}

Which One Should You Choose?

• For most projects: Start with Apache POI. It's widely used, well-documented, and the built-in HTML converter is sufficient for many standard documents. The code is straightforward.
• For high-fidelity, complex documents: Use docx4j. If your DOCX files have complex headers, footers, or intricate formatting that POI struggles with, docx4j will likely produce a more accurate result.
• For clean, simple HTML: Use the POI + jsoup combination. This gives you the power of POI to extract content and the elegance of jsoup to produce clean, web-ready HTML. This is often the best approach for content that will be displayed on a website.