HTML is a widely used markup language that has a simple structure. With a parser generator, one can quickly build a parser for HTML. Alternatively, you can use a popular parser generator as there is various ready-to-use grammar available. You can also use a library for parsing HTML.
This method is more accessible and better as it usually provides more options such as easier navigation or a more accessible easier way to build an HTML document. For instance, it usually comes with the feature, CSS/jQuery-like selector, to locate nodes according to their hierarchy.
This article will discuss practical ways to get the correct library to process HTML using C#, Java, Python, and Javascript.
C# Library to Process HTML
There are many C# libraries to process HTML. The most used ones are discussed in the following.
AngleSharp
For a C# project, you need a modern HTML parser. You can use AngleSharp, an angle brackets parser library. Besides HTML5, it also parses SVG and CSS. It also has an extension that integrates scripting in the competition of parsing HTML documents. Both C# and JavaScript parse HTML based on Jint can be combined with AngleSharp.
This means, after being modified by JavaScript, you can parse HTML documents. It can be done with the JavaScript included in a script you added yourself or on the page. For easy-to-use manipulation, modern conventions like jQuery-like constructs and CSS selectors are fully supported by AngleSharp. Moreover, with support for LINQ for DOM elements.
HTMLAgilityPack
Alternatively, you can opt for HTMLAgilityPack for HTML parsing with C#. Many individuals avoid it as they consider the quality of the code is low. It improved significantly after being revived by ZZZ Projects. This improved version provided accessible documentation. However, it does not support CSS selectors. It only supports XPath and XSLT. HTMLAgilityPack is the best option if you need XPath.
Java Libraries to Process HTML
There are many Java libraries to parse HTML. The widely used ones are discussed in the following.
Lagarto and Jerry
Lagarto is a Jodd component that also functions as an HTML parser. Jerry is another Jodd component that is also known as jQuery in Java. Other components have other functions. For example, CSSelly is a parser for CSS-selectors powers and strings Jerry, whereas StripHtml reduces the size of HTML documents.
Rather than a typical library, Lagarto operates like a traditional parser. You have to create a visitor, and then each time a tag is encountered, the parser will call the proper function. The interface is quite simple; you have to build a visitor called upon each piece of text and each tag. Lagarto only carries out parsing. The DOMBuilder is an extension that creates the DOM tree.
HTMLCleaner
For further HTML processing, you can use HTMLCleaner. It is an open-source HTML parser written in Java. It is developed to clean HTML. It is imperative to clean up the messy ill-formed HTML found on the web for better processing.
For any HTML document, HTMLCleaner puts individual elements and tags in order along with producing well-formed XML. It follows similar rules that most web browsers use to build the Document Object Model by default. For tag balance and filtering, you can provide custom rule sets and tags.
The main drawback of using HTMLCleaner is that its interface is outdated and complex when manipulating HTML. The main advantage is that it operates well on all HTML documents, even the old ones. It can also write the documents in XML besides Pretty HTML. You can opt for HTMLCleaner if you need JDOM and products that support XML and XPath.
JSoup
Jsoup is a Java library designed for working with real-world HTML. Besides working with HTML5, it can deal with both old and bad HTML. With CSS selectors support and DOM Traversal, it possesses a firm license for manipulation. You can also implement removal or addition of HTML quickly with this library.
It can protect the document from XSS attacks or any ransomware attack. It also cleans HTML. Hence, it can improve the formatting and structure of the document. Besides HTML parsing, it can also clean HTML documents and can be very concise.
Python Libraries to Process HTML
There are many Python libraries to parse HTML. The most common ones are discussed in the following.
Standard Python Library HTML Parser
This library is quite rich. Its parser operates like a traditional and simple parser. There are no advanced features. This parser makes a visitor available with essential functions for handling the data at the beginning, inside, and the ending of the tags. It works, but it does not offer any better service than a parser generated by ANTLR and other similar typical parser generators.
Html5lib
Html5lib is an entirely Python-based library for processing HTML. Like all major web browsers, it is developed to conform to the WHATWG HTML specification. Html5lib can take a considerable time, but it is considered an excellent library to process HTML5.
It has a slow process mainly because it is written in Python and not in C. It yields an ElementTree tree by default. Based on xml.dom.minidom, it can also be set to build a DOM tree. It simplifies the serializers and traversing of the tree.
Html5-parser
This parser is written in C, but it is for Python. It is also the kind of parser that only builds a tree. It takes out one function named parse literally. Compared to Html5lib, it operates about 30 times faster. By default, it relies on the library lxml to build the output tree. The same library enables pretty-printing the output. To explain how to move to the resulting tree, Html5-parser refers to the documentation of that library.
Lxml
For processing HTML and XML in Python language, lxml is the easiest-to-use library with the most features. Due to its reliability, speed, and features, it is the most used low-level library for parsing. As it is written in Cython, it relies mainly on the C libraries libxml and libxml2.
It is not limited to a low-level library; other HTML libraries also implement it. The library is developed to operate with the ElementTree API. This API is a container used for storing XML documents in the memory. You can consider it as an old way of managing (X)HTML. With XPath, you are going to search and then operate it like the old-school XML.
Luckily, there is a specific lxml.html that offers few features specifically for HTML parsing. The most important part is that it supports CSS selectors to find the elements easily. There are numerous other features. Some of them are stated in the following:
- It provides an internal DSL for creating HTML documents.
- Forms can be submitted by it.
- It can eliminate unwanted elements from the input, such as CSS style annotations and script content.
AdvancedHTMLParser
This is a Python parser that has the goal to reproduce the behavior of JavaScript in Python. It has to be raw JavaScript, meaning it has no CSS selector syntax or jQuery. Hence, the AdvancedHTMLParser builds an interactive DOM-like representation.
It should operate on an Advanced Tag element with Python if it works in HTML JavaScript. The parser will also require a few additional features. For example, instead of utilizing the JavaScript-like syntax, it supports the direct modification of elements. It can also carry out a basic validation of an HTML document and gives out a prettified HTML output.
The most crucial addition is the support for filtering methods for tags and advanced search. The method finds attributes and search values. The filter is also very advanced. The second one relies on QueryableList, another library. This method is described as ORM-style filtering to any list of items
It does not implement a familiar syntax for HTML manipulation. It is also not as powerful as CSS selectors and XPath. However, when compared to a raw parser, it makes your operation more manageable.
JavaScript Libraries to Process HTML
There are many JavaScript libraries to parse HTML. The most common ones are discussed in the following.
Plain JavaScript or jQuery in Browser
A parser is always included in a browser. Hence, the browser parses the current HTML document by default. HTML parsing is an integral part of JavaScript as it was developed to manipulate the DOM. The browser automatically processes HTML and makes it accessible in the form of DOM.
By parsing the HTML in a new element of the present document, you can use the same functionality. You can choose between the jQuery library and plain JavaScript. To find the DOM elements easily, jQuery provides excellent support for CSS selectors and a few of its selectors. You need a single function, parse HTML, to quickly process the HTML.
Final Thoughts
There are various ways one can parse HTML. Using the appropriate libraries for the necessary programming languages is the main objective of processing HTML.
