Java-Based Web Scraping: Learn The Basics!

When we scrape the web, a question frequently appears: Can we scrape with Java? Read on to find out the process of scraping using Java!

There is a lot of information on the web, which you can use for your own benefit. But gathering the data can be a bit of a hassle. With scraping, you can quickly get those data on hand and ready for use.

With Java tools such as jsoup and HtmlUnit, you can simply collect and parse data from web pages. Then you can embed it into your personal use case for tracking statistics, doing analytics, or delivering a service that uses third-party data.

This article discusses how to scrape the web using Java.

What Is Java?

Java is a platform-independent, object-oriented, and network-centric programming language. Considered one of the fastest, most secure, and most trustworthy languages, it is one of the most widely used in the industry. With fewer implementation requirements, Java is also a platform for building languages.

But can you scrape using Java? The short answer is: Yes, you can!

What Is Web Scraping?

Web scraping is the process of automatically collecting structured web data from websites. It is also known as web data extraction. Some common uses of web scraping include price monitoring, market research, and lead creation, among other things.

For the most part, web scraping is used by individuals and enterprises that wish to make better judgments based on the large quantity of publicly accessible web data.

Web scraping can be done manually, but automated methods are often preferable since they are less expensive and operate more quickly.

You will need a scraper and crawler for web scraping.

The crawler is an algorithm with artificial intelligence that searches the Internet for specific data by following connections.

In contrast, a scraper is a dedicated tool for extracting data from a website. To collect data fast and correctly, the architecture of a scraper can be tailored to the project’s complexity and breadth.

Web Scraping With Java

You might know that you can use multiple programming languages to scrape. Python, C/C++, Node JS, and PHP are some languages that can scrape websites. Java is another popular programming language to use. 

So, in short, Java web scraping or Java-based web scraping is the process of scraping data from a website using the Java programming language.

Basic Process of Web Scraping

The process of web scraping is often broken down into three stages:

1. Proxy and Web Parsing

A scraper must first proxy all of its queries to a target site to mask a user’s IP address.

Webmasters can simply block requests from IP addresses they do not recognize. Therefore this is crucial information to have.

As a result, the scraper must also parse the HTML code of the target page into its integral components to be readily accessible and retrieved.

2. Data Extraction

The scraper can extract whatever data it wants from its target page by parsing HTML. Data in text, photos, or even tables can be included here.

3. Export

It is time for the last step: to export all of the data from the target website into an easy-to-read CSV file.

Why Do You Need to Scrape?

Here are a few reasons, including benefits and use cases, for you to scrape data.

Benefits:

The web scraping method has various benefits, including the following:

• The time necessary to extract information from a source is significantly reduced instead of manually copying and pasting.
• The extracted data is more precise and consistently structured.
• A web scraper can be connected to a system and immediately fed data, significantly increasing automation.

Use Case:

Web scraping is commonly utilized in the real world by businesses for the following reasons:

• Web scraping is a technique used by search engines such as Google to index web pages that eventually show in search results.
• Scrapers are used by communication and marketing departments in various firms to gather information about their organization from the Internet. This enables them to assess their Internet reputation and seek to improve it.
• Web scraping can also detect and monitor the newest online news and trends.
• Certain firms do market research using web scraping by extracting information about their goods and rivals.

These are just a few ways of web scraping that can be used and how it might impact an organization’s operations.

Web Scraping Frameworks

JSoup, Webmagic, and HtmlUnit are the three most often-used libraries for Java-based web scraping.

JSoup is a robust library that is capable of properly handling faulty HTML. The term “tag soup” refers to a faulty HTML page.

HtmlUnit is a graphical user interface (GUI)-free, or headless, browser for Java programs. It can simulate the fundamental parts, such as obtaining specified items from a website, clicking on such elements, etc. 

This library is often used for unit testing, a method of simulating a browser for testing. HtmlUnit can be used for web scraping.

WebMagic is a framework for building scalable crawlers. It manages the crawler’s whole lifecycle: 

• Downloading, 
• URL management, and 
• Content extraction.

It makes the creation of a specialized crawler much easier.

Web Scraping with Java Using JSOUP

HTML parsing in Java is easier using JSOUP, a free and open-source Java tool. With this library, there are several APIs available for retrieving and modifying data obtained through DOM techniques and query selectors.

Dependencies

To use JSOUP, you will need to include it as a dependency in your pom.xml.

Process

1. First, you must get the desired web page and save it as a document data type.
2. Using a CSS query selector, pick the specific page components.
3. Declare an array list to be used to hold the blog titles.
4. Iterate over the retrieved items, “pageElements,” and store them in an array list using an extended “for loop.”
5. Finally, print the array list’s contents.

Web Scraping with Java Using HTMLUnit

HtmlUnit is a Java package that does not provide a graphical user interface for website access. It is an open-source framework with over 21 active contributors.

Dependencies

You can get HtmlUnit from Sourceforge or include it as a dependency in your pom.xml. Then, in the “pom distributionManagement” section, you must provide the repository code.

Process

1. First, select the URL you are willing to scrape. For example, you can use “https://en.wikipedia.org/wiki/Web_scraping” for web scraping.
2. Then you have to pick a web client/ browser. HtmlUnit can simulate various browsers such as Chrome, Brave, Mozilla, Edge, Safari, etc.
3. Following that, you must configure the web client. Defining several settings enhances scraping performance.
4. Then you must deactivate any Javascript exceptions that can occur during the scraping process.
5. You have to fetch the HTML page after configuring the web client.
6. Use CSS queries to get the DOM elements of interest. Selectors are used to select elements in CSS. Selector references are used to get access to DOM elements on a page to customize them.
7. You can pick all the items and save them in a DomNodeList using HtmlUnit.
8. Since each element is retained inside a DomNode data structure, it is necessary to iterate over the DomNodeList. It will print the process’s output.

Web Scraping with Java Using Webmagic

Webmagic is an open-source, scalable crawler developed by code craft. It is based on Scrapy architecture (a popular Python-based library). Additionally, the developers modeled numerous features after the Jsoup library.

Dependencies

You must include it in your pom.xml file as a dependency to use the library. The groupId, artifactId, and version must all be included in your code.

The “slf4j-log4j12” exclusion code must be included in your pom.xml if you have altered your slf4j implementation.

Process

1. Webmagic specified classes must be implemented in “creating the class.” For example, a class called “PageProcessor” is responsible for handling the page’s processing once you define it.
2. The getSite() function retrieves the whole site, whereas the process() method performs all page-related actions.
3. Class variables are used to store site variables. For example, it is possible to set “sleep time” and “retry time” in this case.
4. Add “return site” code to the override getSite() function after defining the Site variable. As a result, the method now returns the value of the site class variable that was initially specified.
5. The selection components must be fetched and stored in a List before being sent to the “processPage()” function.
6. You can print out the contents of the web scraping process by iterating over the string list like previous library implementations.
7. Add the “spider.create” code to the primary function. Then, create an instance of our class and provide the URL to scrape.

Is Web Scraping Legal?

Web scraping is only legal if you scrape publicly available data. When you scrape confidential information, it is not legal.

Conclusion

For business purposes, especially related to research and marketing, scraping the web using Java is a good option. It helps you get the key industry and market info at your fingertips without much hassle or wasting time. 

As the subject of Java web scraping is vast, it is not easy to cover all the essential points in a single reading. Nonetheless, we believe that this article will assist you in learning the fundamentals and making optimum use of it.