GroupDocs Viewer Java – Auto-Detect File Format and Render

Overview

This showcase project demonstrates how to use GroupDocs Viewer (Java) to detect a document format from a file stream and render it to HTML. It is a minimal, runnable Maven project that helps developers understand how to open a document when the format is not taken from the file path.

Prerequisites

• Java Development Kit (JDK) 8 or higher
• Apache Maven 3.5+ installed and added to your PATH
• An Internet connection for Maven to download dependencies

License

GroupDocs Viewer requires a license file to work without evaluation limitations (watermarks, page limits, etc.).

1. Obtain a temporary license – Visit https://purchase.groupdocs.com/temporary-license/ to get a free 30‑day temporary license.
2. Place the license file – Save the downloaded GroupDocs.Viewer.Java.lic file in the project root directory (the same level where pom.xml resides).
3. Without a license – The library will run in evaluation mode which adds watermarks to rendered pages and may impose other restrictions.

Project Structure

auto-detect-file-format-render-groupdocs-viewer-java/
│   pom.xml
│   README.md
│   GroupDocs.Viewer.Java.lic   (optional – place your license here)
│
├───src
│   └───main
│       └───java
│           └───com
│               └───groupdocs
│                   └───viewer
│                       └───examples
│                           └───AutoDetectFileFormatRenderExample.java
│
├───resources
│   ├───input
│   │   └───sample.pdf           (sample PDF – replace with your own)
│   └───output                   (generated HTML pages will be saved here)

Setup & Run

1. Clone or copy the project

   git clone https://github.com/your-repo/auto-detect-file-format-render-groupdocs-viewer-java.git
   cd auto-detect-file-format-render-groupdocs-viewer-java

2. Add your license file (optional but recommended) – copy GroupDocs.Viewer.Java.lic into the project root.
3. Place a document you want to render inside resources/input/. The project already contains sample.pdf, which you can replace.
4. Build the project

   mvn clean compile

5. Run the example
   • Using Maven Exec plugin:

     mvn exec:java

What Happens When You Run It?

• The program loads the license (if present).
• It checks resources/input/sample.pdf. If the file is missing, execution stops with an error message.
• An output directory resources/output/ is created if it does not already exist.
• The file is opened as a stream. FileType.fromStream reads the file signature and prints the detected type.
• The detected type is passed to LoadOptions, and the same bytes are rendered to HTML with names like page_1.html, page_2.html, and so on.
• Console output informs you about the progress and any possible errors.

Customization

• Change output format – replace HtmlViewOptions with PdfViewOptions or PngViewOptions and adjust the output file name.
• Render another document – replace resources/input/sample.pdf with another supported file, or change INPUT_FILE in the source.
• Render a page range – call viewer.view(options, 1, 2) to render the first two pages instead of the whole document.

Notes

• The included sample.pdf is a real PDF document, so format detection and HTML rendering can be checked immediately.
• Detection uses a separate stream from rendering. FileType.fromStream reads the signature and does not rewind the stream.
• Ensure the resources/input/ and resources/output/ directories are at the same level as pom.xml as shown in the structure above.

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This is a showcase project for GroupDocs Viewer. It is intended for demonstration and educational purposes.