How to extract data from HTML page source using Java

There are several ways to extract data from an HTML page source within a webpage using Android Studio and Java. One popular way is to use a library such as Jsoup to parse the HTML and extract the data.

why do we need to extract data from HTML?

There are several reasons why someone might need to extract data from an HTML page:

  1. Data mining: Extracting structured data from a webpage can be useful for data mining and data analysis. This can be used for a variety of purposes, such as for business intelligence, scientific research, or for creating machine learning models.
  2. Web scraping: Extracting data from webpages can be used for web scraping, which is the process of automatically collecting and processing data from the internet. Web scraping can be used for a variety of purposes, such as for price comparison, content aggregation, or for creating a dataset for machine learning.
  3. Automation: Extracting data from webpages can also be used to automate tasks such as filling out forms, logging in to websites, or navigating through a site’s pages.
  4. Creating a web bot: Extracted data can be used to create a web bot, which is a program that can automate tasks on the internet, such as posting comments, filling out forms, or buying items online.
  5. Displaying information: Extracting data from HTML can also be used to create a better user experience by displaying the information in a more appropriate format. For example, a news website may use extracted data from the HTML to display news in a more readable format on their mobile application.

Overall, extracting data from HTML can be useful in various fields, and can automate various tasks and enable the creation of new features and functionalities.

Extract Data with Java (Jsoup).

Jsoup is a Java library that can be used to parse and extract data from an HTML or XML document. You can use it to extract data from a webpage by making a request to the webpage, and then parsing the response. Here is an example of how you can use Jsoup to extract the text of all the <p> elements from a webpage:
// Connect to the webpage
    Document doc = Jsoup.connect("http://example.com").get();
    
    // Find all the <p> elements
    Elements paragraphs = doc.select("p");
    
    // Extract the text of each <p> element
    for (Element p : paragraphs) {
        String text = p.text();
        System.out.println(text);
    }

You can also use css selectors to select specific elements and retrieve specific attributes of elements.

  Elements links = doc.select("a[href]");
    for (Element link : links) {
        String linkHref = link.attr("href");
        String linkText = link.text();
        System.out.println("Href: " + linkHref + " Text: " + linkText);
    }

You can also use Jsoup to modify the HTML and add, remove or edit elements as well.

Please note that You will have to add Jsoup dependency in your build.gradle file.
  implementation 'org.jsoup:jsoup:1.14.3'

Also, you need to handle internet permission in the manifest file.

It’s important to keep in mind that the content of the web page may change, so the data extraction method can break in the future. Always test the extraction on different web pages with different structures.
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