A Complete Guide on Web Scraping Using Java

by · Published · Updated

Wondering how to scrape the web? Java is the answer. Read this article to get a clear idea of how to use Java for web scraping.

In this day and age, data is everything. The amount of data we use or refer to every single day is staggering, and something we have little idea about. The value of data is vast and limitless, ranging from a primary school student reading writings online to a rich entrepreneur receiving information from different websites.

Effective and ineffective data can make or break an organization respectively. Company owners leave no stone unturned to establish benchmarks, set targets, and project predicted outcomes – all based on data. So how is all this data collected? This is where the concept of web scraping comes into play.

In today’s rapidly evolving digital landscape, it’s imperative for individuals and businesses alike to watchout for malware that can infiltrate systems without a trace. Often, cybercriminals deploy these malicious software pieces through seemingly harmless activities, such as web scraping, which involves automatically extracting information from websites. While web scraping itself can serve legitimate purposes, when misused, it can act as a gateway for malware, putting sensitive data and system integrity at risk. Hence, staying vigilant and informed is crucial in this interconnected world.

The purpose of this article is to explain what web scraping is, as well as guide you on how to set up your web scraper with the use of Java – a renowned programming language.

What is Web Scraping

In simple terms, web scraping is similar to a person manually copying text from a source. However, the difference lies in the speed of operation as scraping can extract mammoth chunks of data in the blink of an eye. Many websites refuse to provide the data they contain through public APIs. This means, to extract data from these sites, something different needs to be done.

Web scraping does just that, as scrapers can extract data straight from the browser. Many, upon the first introduction, find this process of data accumulation to be ineffective. However, if you think about it, more information is never a bad thing.

The more well-informed company owners are, the better the decisions taken by them. As the internet is growing at an exponential rate these days, opting for manual methods of data collection is not an option anymore. Automated methods are mandatory to keep up with all the data being generated each day. Thus, web scraping is the way to go.

What Is Java and Why Is a Java API Needed for Web Scraping?

Java is a programming language that is regarded as one of the pioneering endeavors in programming in general. It is completely open-source and object-oriented, which adds to its fame and utility.

Over the years, a lot of changes have been made in the core language to decrease the dependencies of code implementation. This has contributed to a rise in the number of Java developers over the years which, in turn, has made the language more viable to be used in a lot of sectors, including scraping the web.

When it comes to web scraping in Java, a whole lot can be done, ranging from creating productive APIs to implementing external APIs using the language.

Java web scraping methodologies not only deal with hurdles like IP-blocking, geo-blocking, honeypots, and CAPTCHAs but also collect data with extreme efficiency, compared to other languages. While there is nothing wrong with building an “okay” scraper using some other language, the quality of the scraper does make a difference in terms of accessibility and speed. Thus, Java is a recommended programming language for web scraping purposes.

How to Build a Web Scraper Using Java?

To build a web scraper in Java from scratch, you would need specific information regarding how to initiate the whole Java-development setup, and then go on adding the necessary codes into the program. The following sections explain all the steps that you would need to take.

Set Up the Java Runtime Environment

There are certain prerequisites to building a Java program of any sort. Below is a list of systems that you would need to integrate to be able to start writing code in Java.

  • Java 8: Despite the release of versions as high as 11, established developers still prefer using version 8, simply because of the ease of creating web scrapers in it.
  • IDE: Although anything can be used, IntelliJ IDEA is arguably the best of the lot, due to its easy integration with Gradle.
  • Gradle: It is a build automation tool that can manage dependencies.
  • HtmlUnit: It is a browser for Java programs, without a GUI. It can

To check if all the systems are properly integrated, try opening a terminal and running the commands listed below.

> java -version

> gradle -v

If everything is up and running, these commands would display the existing versions of Java and Gradle in the system.

Create a Project

Once all the prerequisites are active, it is time to install HtmlUnit in the project. Open the file called “build.gradle”. Here, the following line of code needs to be added in the “dependencies” section.

implementation(‘net.sourceforge.htmlunit:htmlunit:2.51.0’)

If the code is entered the right way, HtmlUnit should be installed in your program.

Inspect the Targeted Page

Visit the page you intend to scrape. Right-click anywhere on the page, and click on “Inspect”. This opens up the developer console of the page, where you would be able to see all the HTML used in it. Do not be overwhelmed by all the complex tags and class declarations. You would not need to understand the functionalities of most of it during the process of developing the web scraper.

Transmit an HTTP Request to Initiate the Data Extraction

Now that all the necessary HTML is located and identified, it is time to bring a copy to your local device. An HTTP request needs to be sent by using HtmlUnit. This calls the code and fetches a document where all the Html is written.

To initiate the functions of HtmlUnit, certain Java libraries need to be imported, which includes IOException and List. HtmlUnit also needs to import again for the new codes to compile and run according to the standards set by the browser.

A WebClient is then initialized to send the HTTP request to the targeted page for fetching an HtmlPage. Make sure you stop the process right after you finish extracting your intended data. If not, the program will continue running until no data remains to be scraped.

Handle the Errors

The moment you initiate HtmlUnit, you will be bombarded with a handful of error messages displayed on the console. Do not be perturbed. This is very common when using HtmlUnit, and about 98% of the errors can simply be ignored without any notable consequences.

However, the ones that are significant errors do need to be handled. Check the syntaxes, method calls, library imports, and run a complete debug to identify the errors and fix them.

Scrape the Desired Data

As it stands, you have an HTML document that is not human-readable. However, you need data that you can read and understand. To achieve that, you would need to write some more code.

To extract the title of the website, Java’s getTitleText method can be used. For all the links, the getAnchors and getHrefAttribute methods are ideal. Upon extraction, the information can be displayed on the screen by using the println method in Java.

You can use all the aforementioned methods courtesy of HtmlUnit. You can adopt completely manual methods and write all the code on your own. However, that would take significantly more time and is a problem that is effectively solved by HtmlUnit.

In this manner, you can extract seemingly anything that exists on the page. All you need is to identify the tags in which the desired data lie. After that, you can simply call the relevant method and obtain the data.

Transfer the Data to a CSV File

Onto the last stage where you would transfer the extracted information to a CSV file. To create the document, start by importing the FileWriter library. This builds the CSV in “append” mode, which is what you need for making edits.

Afterward, the head or first line of the CSV needs to be created, which you can either do by calling a method or manually writing on your own. The rest of the data can then be called according to their locations and tags (just like the title), and entered in the CSV by using the .write method in Java. Close the file by using the .close method, which would mark the end of the entire process.

You should be left with a CSV file full of data from the targeted page or website. The data should be categorically classified if you called and executed the Java methods by following a plan.

Final Words

Although web scraping can be done using Python tools, the same can be done with Java, and quite remarkably with shorter lengths of code. We believe this article has been able to provide you with a clear idea regarding the method of implementing Java codes to build an effective web scraper from absolute scratch. Make sure you play with the codes and learn more as you dig deeper into the world of Java and web scraping.