The Top 25 Jsoup Interview Questions To Prepare For Your Next Tech Interview

Jsoup has become an essential Java library for web scraping, cleaning user-submitted content, and testing HTML validity. As one of the most popular HTML parsers for Java, knowledge of Jsoup is a highly sought-after skill for developers and test automation engineers.

Whether you have an upcoming interview or simply want to expand your Jsoup skills, this comprehensive guide on Jsoup interview questions will take your technical preparation to the next level. We’ve compiled a list of the top 25 questions frequently asked about Jsoup during job interviews, complete with example responses to help you formulate your own winning answers

Let’s dive in and start prepping for your next Jsoup discussion!

Getting Started with Jsoup

Jsoup is open source Java HTML parser designed for fetching, parsing, manipulating and cleaning HTML. It provides idiomatic Java API for handling real-world messy HTML.

Here are some key aspects of Jsoup:

• Parses HTML from URL, file or string
• Finds and extracts data using DOM traversal or CSS selectors
• Manipulates HTML elements, attributes, text
• Handles malformed HTML
• Clean user-submitted content against whitelist

Q1. What are the key benefits of using Jsoup over other HTML parsers in Java?

Some major advantages of using Jsoup are:

• Simple and intuitive API
• DOM traversal using jQuery-like methods
• Tolerant of malformed HTML
• Flexibility to parse HTML from URL, file or string
• Built-in methods for cleaning untrusted content
• Good performance for large documents
• Active community support

Compared to parsers like JDOM and DOM4J, Jsoup provides a much friendlier API and ability to handle real-world HTML soup.

Q2. How does Jsoup handle malformed HTML documents?

Jsoup uses a tolerant HTML parser that balances tag structure even when the original HTML is malformed. It applies a tag balancing algorithm to ensure every start tag has a corresponding end tag.

This can sometimes lead to unexpected parsing results compared to browser DOM, especially with unclosed tags and improper nesting. Script and style elements are also ignored syntactically by Jsoup.

So while Jsoup tries to clean up and make sense of malformed markup, it can misinterpret implicit structure leading to parsing differences from browser DOM.

Q3. What is the difference between Jsoup.connect() and Jsoup.parse() methods?

• Jsoup.connect() – Creates a new connection to fetch and parse HTML from a URL. Requires network call.

• Jsoup.parse() – Parses HTML from a String or File. No network call, direct parsing.

So connect() is used for fetching HTML from web, while parse() works without network directly on a String or File input.

Extracting Data with Jsoup Selectors

One of Jsoup’s most powerful features is the use of CSS selectors for extracting data out of HTML documents. Here are some common Jsoup selector questions you may encounter:

Q4. How can we select an element by ID in Jsoup?

Use the CSS selector #id to select element by ID.

For example:

Document doc = Jsoup.parse(html);Element content = doc.select("#main-content").first();

This selects the element with id “main-content”.

Q5. How to select all hyperlinks in a Jsoup document?

To select all hyperlink elements <a> in a Jsoup document, use the selector:

a[href]

For example:

Elements links = doc.select("a[href]");

This will select <a> elements with an href attribute i.e. hyperlinks.

Q6. How can we get text content of all <p> elements?

To extract text content of all paragraph <p> elements:

Elements paragraphs = doc.select("p");for (Element p : paragraphs) {  String paraText = p.text();}

The text() method on an Element returns inner text recursively.

Manipulating HTML with Jsoup

Jsoup allows modifying and manipulating HTML elements, attributes, text etc. Here are some common interview questions on how to manipulate HTML with Jsoup:

Q7. How to change the text inside an element in Jsoup?

Use the text() method on the Element, passing the new text as parameter.

For example:

Element heading = doc.select(".heading").first();heading.text("New heading text");

This will replace existing text inside <h1 class="heading"> with “New heading text”.

Q8. How can we add attributes to an element in Jsoup?

Call the attr() method on Element, passing attribute key and value to set.

For example:

Element link = doc.select("a").first();link.attr("target", "_blank"); // add target="_blank" 

Q9. How to modify inner HTML of an element in Jsoup?

Use the html() method on Element, pass the new HTML as String:

Element div = doc.select("#content").first();div.html("<p>New HTML</p>");

This will replace existing HTML inside <div id="content">

Cleaning HTML with Jsoup

Jsoup comes with a built-in HTML cleaner to sanitize untrusted user content. Here are some key interview questions on cleaning HTML with Jsoup:

Q10. How can we remove all attributes from elements in Jsoup?

To remove all attributes from elements:

doc.getAllElements().removeAttr("style"); // remove style attr

We can also remove specific attributes:

doc.select("img").removeAttr("width"); //remove width attr from images

Q11. How to whitelist only safe tags and attributes in Jsoup?

• Use Jsoup Cleaner and configure a Whitelist containing only safe tags/attributes.

• Clean user submitted HTML against whitelist:

String unsafe = ...; Whitelist whitelist = Whitelist.basic();String safe = Jsoup.clean(unsafe, whitelist); 

This removes all tags/attributes not in basic whitelist.

Q12. How can we strip all tags from an HTML document in Jsoup?

Use Jsoup’s text() method on Document to get plaintext with all tags stripped:

String text = doc.text(); // strip all HTML tags

To select an element and get just its text content:

String divText = doc.select("div").first().text();

Jsoup Tips and Tricks

Here are some advanced Jsoup interview questions to demonstrate your expertise:

Q13. How to get full absolute URL from a relative anchor href?

Use absHref() method:

String fullUrl = link.attr("abs:href"); 

abs: prefix resolves relative URL to absolute.

Q14. How can we get request response headers and status in Jsoup?

After Connection.execute():

int status = response.statusCode();Map<String, String> headers = response.headers();

Q15. How to submit a form with Jsoup?

• Fetch and parse form page
• Select form using doc.select("#myForm")
• Populate form data using form.getElement("#username").val("bob")
• Submit form using form.submit()

This will handle form submission automatically.

Q16. How can we log Jsoup debug messages?

Enable Jsoup debug logging:

Jsoup.log(LogLevel.DEBUG, "jsoup");

This prints debug info like request URL, response headers etc.

Common Jsoup Interview Questions

Here are some additional popular Jsoup interview questions:

Q17. Can you explain how Jsoup handles cookies and maintains sessions?

Jsoup handles cookies via the Connection interface. Use Connection.cookie(name, value) to set request cookies for maintaining sessions.

Q18. How does Jsoup handle HTTP requests and responses?

Jsoup provides Connection interface to handle HTTP requests. Use methods like get() and post() to send requests and get response HTML. Internally it uses HttpURLConnection.

Q19. How can we parse XML documents using Jsoup?

Jsoup can parse XML using the Jsoup.parse(stringOrFile, baseUrl) method. This returns a Document which can be traversed like HTML DOM via Jsoup APIs.

Q20. What are some limitations of using Jsoup you’ve faced?

Some limitations are:

• Handling large documents can cause memory issues