If you're using Eclipse to develop a Java web application, you can use Apache Commons FileUpload to handle file uploads in a servlet. Here's how to set up a file upload servlet using Eclipse and Apache Commons FileUpload:

1. First, create a new dynamic web project in Eclipse. Choose "File" > "New" > "Dynamic Web Project" and give your project a name.

2. Add the Apache Commons FileUpload library to your project. You can do this by downloading the library from the Apache website and adding the JAR file to your project's classpath.

3. Create a new servlet in your project. Choose "File" > "New" > "Servlet" and give your servlet a name.

4. In the doPost() method of your servlet, create a ServletFileUpload object and use it to parse the HTTP request.

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // Create a new file upload handler
    ServletFileUpload upload = new ServletFileUpload();

    // Parse the request
    FileItemIterator iter = upload.getItemIterator(request);
    while (iter.hasNext()) {
        FileItemStream item = iter.next();
        String name = item.getFieldName();
        InputStream stream = item.openStream();
        if (!item.isFormField()) {
            // Process the file
        }
    }
}

5. The ServletFileUpload object is used to parse the HTTP request and extract any uploaded files. The FileItemIterator is used to iterate over all the items in the request. For each item, we use the FileItemStream object to obtain the field name and input stream. If the item is a file (as opposed to a regular form field), we can process it as needed.

6. To create a JSP page that includes a file upload form, you can use the following code:

<form action="FileUploadServlet" method="post" enctype="multipart/form-data">
    <input type="file" name="file">
    <input type="submit" value="Upload">
</form>

7. In the JSP page, the enctype attribute of the form element is set to multipart/form-data, which tells the browser to send the data as a multi-part form.

8. When the user submits the form, the FileUploadServlet servlet will handle the file upload as described above.

Overall, Apache Commons FileUpload provides a simple and powerful way to handle file uploads in a servlet-based web application. With a few lines of code, you can easily handle file uploads and integrate them into your application.