What is web crawling?
A web scraper or a web crawler is a tool or a library that performs the process of automatically extracting the selective data from web pages on the Internet. Numerous web scrapers have played significant roles in the rapid increase in big data applications. Due to these tools, developers were able to collect a huge amount of data very easily and quickly that was later used for researches and big data applications.
Java web crawling
Like many other programming languages, Java is one of the most dominating programming languages in the industry also offers a variety of Java web crawlers. These web scrapers allow Java developers to keep coding on their existing Java source code or framework and help in scraping data for various purposes in a fast, simple but extensive way.
Top 10 Java web crawling libraries
We will walk through the top 10 recent Java web crawling libraries and tools that you can easily use to collect the required data in 2021,
First on the list is Heritrix. It is an open-source Java web crawling library with high extensibility and is also designed for web archiving. It also provides a very easy-to-use web-based user interface accessible with any modern web browser that can be used for operational controls and for monitoring the crawls.
Its highlighted features include:
- A variety of replaceable and pluggable modules.
- An easy-to-use web-based interface.
- It also comes with Excellent extensibility.
Web-Harvest is another exceptional open-source java crawling tool. It offers the feature for collecting useful data from selective web pages. To successfully achieve that, it mostly relies on XSLT, XQuery, and Regular Expressions to search and filter content from HTML and XML-based websites. It can also be easily integrated with custom Java libraries to further utilize its extraction capabilities.
Its best features are:
- Powerful XML and text manipulation processors for handling and controlling the flow of Data.
- It also comes with variable context for using and storing variables.
- Other scripting languages are also supported, which can be easily integrated within the scraper configurations.
3. Apache Nutch
Apache Nutch is a unique Java web crawling tool that comes with a highly modular architecture. It allows Java developers to create custom plug-ins for applications like media-type parsing, data retrieval, querying, and clustering. Due to being pluggable and modular, Apache Nutch comes with an extensible interface to adjust all the custom implementations.
Its main advantages are:
- It is a highly extensible and scalable Java web crawler as compared to other tools.
- It follows all the text rules.
- Apache Nutch has an existing huge community and active developers.
- Features like pluggable parsing, protocols, storage, and indexing.
Its highlighting features are:
- It processes every HTTP Request/Responses individually.
- Easy to use interface with REST APIs
- It offers support for HTTP, HTTPS & basic auth
- It also offers RegEx-enabled querying in DOM & JSON
StormCrawler is a full-fledged Java web crawler. It offers a collection of reusable features and components, all of them mostly written in Java. It is one of the most suited tools for building low-latency, scalable and optimized web crawling solutions in Java and also is perfect to serve streams of URLs for crawling.
Its unique features include:
- It is a highly scalable Java web crawler and can be used for big-scale recursive crawls.
- It is easy to extend with additional Java libraries
- It also provides a proper thread management system that reduces the latency of every crawl.
Gecco is a complete framework designed for Java web crawling. It is a lightweight and easy-to-use web crawler completely written in Java language. Gecco framework is preferred mainly for its exceptional scalability. This framework is developed primarily based on the principle of open and close design, the provision to modify the closure, and the expansion of the open.
Gecco’s main pros are:
- Its support for asynchronous Ajax requests in the web pages.
- It also provides support to the download proxy servers that are used to access geographically restricted websites.
- It allows the use of Redis to realize distributed crawling
WebSPHINX (Website-Specific Processors for HTML Information extraction) is an excellent Java web crawling tool as a Java class library and interactive development environment for various other web crawlers. WebSPHINX consists of two main parts: first, the Crawler Workbench and the WebSPHINX class library. It also provides a fully functional graphical user interface that lets the users configure and control a customizable Java web crawler.
Its highlighting feature is:
- WebSPHINX offers a user-friendly GUI.
- An extensive level of customization is also offered.
- It can be a good addition to other web crawlers.
Jsoup is another great option for a Java web crawling library. It allows Java developers to navigate the real-world HTML. It is also preferred by many developers prefer it over many other options because it offers quite a convenient API for extracting and manipulating all the collected data by making use of the best of DOM, CSS, and jquery-like methods.
Its advantages are:
- Jsoup provides complete support for CSS selectors.
- It sanitizes HTML.
- Jsoup comes with built-in proxy support.
- It provides an API to traverse the HTML DOM tree to extract the targeted data from the web.
Its promising features include:
- The support for simulating browser events.
- It offers Xpath based parsing.
- It can also be an alternative for unit testing.
10. Norconex HTTP Collector
Norconex is the most unique Java web crawler among all as it is targets the enterprise needs of a user. It is a great crawling tool as it enables users to crawl any kind of web content that they need. It can even be used as a full-featured collector or users can embed it in their application. It is compatible with almost every operating system. Due to being a large-scale tool, it can crawl up to millions of pages on a single server of medium capacity.
The prominent features by Norconex include:
- It is highly scalable as it can crawl millions of web pages.
- It also offers OCR support to scan data from images and PDF files.
- You can also configure the crawling speed
- Language detection is also supported, allowing users to scrap non- English sites.
As the applications of web scraping are increasing, the use of Java web crawling tools is also set to rapidly grow. As there are many Java crawler libraries now available, and each one offers its unique features, users will have to study some more web crawlers to find the one that suits them best and fulfill all their needs. It will help them easily leverage these tools to power the web scraping task for their data collection.