Implementing Online Preview of Office Documents in Java Using OpenOffice and JODConverter

Online preview of office documents (Word, Excel, PowerPoint, txt) is a common requirement; this guide shows how to achieve it for free using Apache OpenOffice as a conversion engine and the JODConverter library in a Java backend.

First, download and install Apache OpenOffice from the official site. After installation, add the JODConverter dependency to your Maven pom.xml :

<!--openoffice-->
<dependency>
    <groupId>com.artofsolving</groupId>
    <artifactId>jodconverter</artifactId>
    <version>2.2.1</version>
</dependency>

Next, create a utility class FileConvertUtil that handles conversion of local and remote files to PDF streams. The class establishes a socket connection to the OpenOffice service (default port 8100), uses StreamOpenOfficeDocumentConverter to convert the input stream, and returns the resulting PDF as an InputStream . It also includes a helper method to convert an OutputStream back to an InputStream .

import com.artofsolving.jodconverter.DefaultDocumentFormatRegistry;
import com.artofsolving.jodconverter.DocumentConverter;
import com.artofsolving.jodconverter.DocumentFormat;
import com.artofsolving.jodconverter.openoffice.connection.OpenOfficeConnection;
import com.artofsolving.jodconverter.openoffice.connection.SocketOpenOfficeConnection;
import com.artofsolving.jodconverter.openoffice.converter.StreamOpenOfficeDocumentConverter;
import java.io.*;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;

public class FileConvertUtil {
    private static final String DEFAULT_SUFFIX = "pdf";
    private static final Integer OPENOFFICE_PORT = 8100;

    public static InputStream convertLocaleFile(String sourcePath, String suffix) throws Exception {
        File inputFile = new File(sourcePath);
        InputStream inputStream = new FileInputStream(inputFile);
        return covertCommonByStream(inputStream, suffix);
    }

    public static InputStream convertNetFile(String netFileUrl, String suffix) throws Exception {
        URL url = new URL(netFileUrl);
        URLConnection urlconn = url.openConnection();
        urlconn.connect();
        HttpURLConnection httpconn = (HttpURLConnection) urlconn;
        int httpResult = httpconn.getResponseCode();
        if (httpResult == HttpURLConnection.HTTP_OK) {
            InputStream inputStream = urlconn.getInputStream();
            return covertCommonByStream(inputStream, suffix);
        }
        return null;
    }

    public static InputStream covertCommonByStream(InputStream inputStream, String suffix) throws Exception {
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        OpenOfficeConnection connection = new SocketOpenOfficeConnection(OPENOFFICE_PORT);
        connection.connect();
        DocumentConverter converter = new StreamOpenOfficeDocumentConverter(connection);
        DefaultDocumentFormatRegistry formatReg = new DefaultDocumentFormatRegistry();
        DocumentFormat targetFormat = formatReg.getFormatByFileExtension(DEFAULT_SUFFIX);
        DocumentFormat sourceFormat = formatReg.getFormatByFileExtension(suffix);
        converter.convert(inputStream, sourceFormat, out, targetFormat);
        connection.disconnect();
        return outputStreamConvertInputStream(out);
    }

    public static ByteArrayInputStream outputStreamConvertInputStream(final OutputStream out) throws Exception {
        ByteArrayOutputStream baos = (ByteArrayOutputStream) out;
        return new ByteArrayInputStream(baos.toByteArray());
    }
}

In the service layer, expose a method onlinePreview that validates the file extension, calls FileConvertUtil.convertNetFile to obtain the PDF stream, and writes the stream to the HTTP response.

public void onlinePreview(String url, HttpServletResponse response) throws Exception {
    String[] str = SmartStringUtil.split(url, "\\.");
    if (str.length == 0) {
        throw new Exception("文件格式不正确");
    }
    String suffix = str[str.length - 1];
    if (!suffix.matches("txt|doc|docx|xls|xlsx|ppt|pptx")) {
        throw new Exception("文件格式不支持预览");
    }
    InputStream in = FileConvertUtil.convertNetFile(url, suffix);
    OutputStream outputStream = response.getOutputStream();
    byte[] buff = new byte[1024];
    int n;
    while ((n = in.read(buff)) != -1) {
        outputStream.write(buff, 0, n);
    }
    outputStream.flush();
    outputStream.close();
    in.close();
}

The controller simply forwards the request to the service:

@ApiOperation(value = "系统文件在线预览接口")
@PostMapping("/api/file/onlinePreview")
public void onlinePreview(@RequestParam("url") String url, HttpServletResponse response) throws Exception {
    fileService.onlinePreview(url, response);
}

After deploying the application and ensuring OpenOffice is running on port 8100, accessing the endpoint with a file URL returns a PDF stream that browsers can display directly, providing seamless online preview for various office formats.

Images in the original article demonstrate the preview results for Excel and Word files.