To achieve this task, you will need to scan all the reference links in the HTML document for additional assets such as images and scripts. Once identified, download these assets locally and then update the HTML document to reference the local copies. You can accomplish this using a library like Jsoup:
Identify and extract all img elements present on the page,
Retrieve the URL of the image file from the src attribute of each img element (using .attr("abs:src")),
Download these images to a designated local directory,
Update the src attributes of the image elements to point to the location of the downloaded image files, relative to where the main HTML file is stored e.g., with
.attr("src", "assets/imagefilename.png")
.Repeat this process for other required assets like CSS, scripts, HTML5 videos, etc. Additionally, handling background image references and other elements found in CSS through regex operations may also be necessary. Webpages often include linked items such as favicons and RSS feeds that should be considered as well.
Save the modified Jsoup document (with updated URLs pointing to the locally saved assets) by converting it to a string with .toString() and saving the output to a file.
You can then view the updated HTML file in a webview, ensuring that all images and assets are displayed correctly even when offline.
An Android app I developed performs these exact tasks by saving a complete HTML file along with CSS, images, and other assets locally using Jsoup.
For more information, visit https://github.com/UniqueApp/, particularly SaveService.java for the code related to saving and downloading HTML pages.
Kindly note that this app is GPL licensed, so adherence to the license terms is mandatory if utilizing any part of it.
Also, please be aware that the app handles various functionalities and may appear disorganized without proper comments or documentation. However, it can still be beneficial for your needs.