How To Get Started Web Scraping With Java

So, you’ve decided to take advantage of web scraping to gather data, and now you need to build a bot to do it. Even cursory research into building web scrapers will tell you several different programming languages exist that could help you accomplish that goal.

Which one is the “right” one? It depends. Many web scrapers are built on the Python programming language, but runtime environments like Node.js allow scrapers to be built with Javascript (Java).

Web scraping with Java offers multiple benefits, including:

  • Greater speed
  • The ability to handle static and dynamic web pages
  • Integrated with useful application programming interfaces (APIs) and node modules

In this blog, we’ll go over what tools you’ll need to build a Java web scraper, what makes Java unique when it comes to web scraping, the best way to use proxies with the web scraper you build, and more.

What You’ll Need to Get Started‌ Java Web Scraping

java web scraping

First off, you’ll need a working knowledge of Javascript, as well as an understanding of HTML and how to select elements within HTML code. There are a few ways to build a Java scraper, so depending on which you choose, you’ll need any of the following:

JSoup and HtmlUnity are both class libraries — commonly just referred to as “libraries” — you can use with Javascript. In Java terms, a library is basically a set of classes that someone else has already written that you can download and plug into your crawler.

Once you download the library, your computer will be able to recognize and work with that code. Libraries are useful because they’re ready-made code that people have already tested that you can simply download and use to expand the functionality of Java on your own device. JSoup and HtmlUnit are two of the more popular libraries out there, but many more exist.

Maven is a tool made by Apache that allows you to automate Java projects. It’s open-source and free to download from Apache’s website. Maven can work with plugins that expand its functionality, letting it generate a PDF display of your project or a list of recent changes from your source code management (SCM).

Choose which library you want to use, download the necessary programs, and you’re ready to get started building your web scraper.

Web Scraping With Java Using Asynchronous Code‌

web scraping in java with jsoup

The very definition of web scraping is retrieving data, and large amounts of it. So, the way your scraper handles that data is worth considering. If it can’t handle large amounts of data, well, it could slow your scraper down.

Javascript handles data synchronously, meaning it executes events line by line and waits for one to finish before it starts the next. The process of fetching data from a website, however, is asynchronous — it involves code separate from the regular synchronous order of events.

You can combine these two types of code using Java to scrape data from the web, using two keywords: async and await. These keywords allow asynchronous code to look much cleaner and closer to regular synchronous Java code. Here’s an example of how that syntax looks:

/* Async/Await Syntax */

(async () => {

try {

  const result = await doSomething();

  const newResult = await doSomethingElse(result);

  const finalResult = await doThirdThing(newResult);

  console.log(finalResult);

} catch(err) {

  console.log(err);

})();

And an example of how that would’ve looked before these keywords were introduced:

/* Passed-in Callbacks */

doSomething(function(result) {

doSomethingElse(result, function(newResult) {

  doThirdThing(newResult, function(finalResult) {

    console.log(finalResult);

  }, failureCallback);

}, failureCallback);

}, failureCallback);

Building Your Web Scraper‌: Scraping With Java In Jsoup

web scraping using java Jsoup

Now, you can learn how to build your Java web scraper using the Jsoup library. You’ll need that and Maven, so be sure to download both before you start.

You’ll follow three broad steps to scrape using Java with Jsoup:

  • Get the Jsoup library
  • Get and parse the HTML code from the web
  • Query the HTML code

We’ll start with step one.

Getting Jsoup‌

Download the library from the page linked earlier in this blog. After that, you’ll want to set up Maven to work with your chosen library, which in this case is Jsoup. To set that up you can use any Java integrated developer environment (IDE) and create a new Maven project.

In the project object model (POM) file, called the pom.xml file, you’ll add a new section for dependencies. Then, add a new dependency for Jsoup. That will look something like this:

<dependencies>

  <dependency>

      <groupId>org.jsoup</groupId>

      <artifactId>jsoup</artifactId>

      <version>1.14.1</version>

  </dependency>

</dependencies>

Once this is done, you’re primed to build your Java web scraper.

Getting and parsing the HTML‌ in Java

Part two of this process is retrieving the HTML from your target website and parsing it into a Java object. You can use the following import code to get the HTML:

import org.jsoup.Connection;

import org.jsoup.Jsoup;

import org.jsoup.nodes.Document;

import org.jsoup.nodes.Element;

import org.jsoup.select.Elements;

There are other import commands you can use, so you should be sure to only use the ones that will get you the data you need. A good rule of thumb to follow when web scraping with Java is: If you don’t need to grab everything, don’t.

JSoup will use the “connect” function to take the website’s URL and return a document to you with all the data it retrieved. Say you wanted to scrape the Wikipedia entry on JSoup, for example. You would use the following command to grab that page’s HTML code:

Document doc = Jsoup.connect(“https://en.wikipedia.org/wiki/Jsoup”).get();

You could also create a function to retrieve that same data which uses your target website URL as a parameter. This is less likely to return an error than the “.get()” method displayed above. That function would look like this:

public static Document getDocument(String url) {

  Connection conn = Jsoup.connect(url);

  Document document = null;

  try {

      document = conn.get();

  } catch (IOException e) {

      e.printStackTrace();

  // handle error

  }

  return document;

Another best practice to avoid common errors when web scraping this way is to send the user agent string to the userAgent() function before calling the get() function. Doing that helps you get past a custom user agent, and the code would look like this:

Connection conn = Jsoup.connect(url);

conn.userAgent(“custom user agent”);

document = conn.get();

Querying the HTML code‌

Now comes the point of the entire exercise: getting the information you want. That’s done by having your Java scraper query the HTML ”document” object for the data you need. It’s probably the most labor-intensive part of writing your Java web scraper.

JSoup gives you multiple methods to extract the data you want from the HTML code. You’ll usually do it by using elements like “getElementByID,” or “getElementsByTag” to query the document object model (DOM) of your target URL.

Pay attention to whether the commands you use are singular or plural. Using “getElement” will return one element, while “getElements” will return an array list of “element” objects.

While some elements available to you will be specific to JSoup, others can be used more widely. It’s good practice to get familiar with those elements in case you want to work with another library like HtmlUnit in the future.

The “select” method, for example, lets you select a certain object from a list. The “parent” and “child” elements let you traverse up a page. And those are just a couple of examples. For a comprehensive list of document navigation elements, browse here.

Which elements you use and how specific you get with your queries will depend on the data you’re trying to retrieve, and that will determine how your Java scraper gets written.

Java Web Scraping With Proxies

java web scraping with proxy

Once your Java web scraper is built to your specifications, you’ll need to pair it with proxies to get the most out of it. You probably already know why proxies are important, but may not be sure of the best ones to use for web scraping.

Proxies largely come in two varieties: data center proxies and residential proxies. Data center proxies switch out your device’s IP address but identify themselves as coming from a data center. They aren’t associated with an internet service provider (ISP). They’re pretty good for web scraping, but don’t provide as much anonymity as residential proxies.

Residential proxies are associated with an ISP. They use the IP addresses of regular devices, like smartphones or laptops, to make it seem as though a page request is being made by an everyday person. This makes it less likely that you’ll be banned, as site owners want to avoid unnecessarily banning regular people.

Blazing SEO uses high-quality residential proxies that are always ethically sourced, and each use case is carefully reviewed before being sold. It’s easy to find proxies online, but if you’re serious about web scraping — and doing it ethically — our proxies are the way to go.

Rotating residential proxies offer the highest degree of anonymity when web scraping. Paired with your Java web scraper, you’re much less likely to be banned, blocked, or hit with a CAPTCHA. We review each purchase of rotating residential proxies to be sure they aren’t used for anything illegal.

The Takeaway‌

web scraping with java

As long as you’ve got a little programming knowledge, building your own web scraper with Java is definitely doable. All the tools you need are free to download and open-source, and there are a multitude of options to choose from.

We’ve gone over how to web scrape with JSoup here, but feel free to investigate other libraries to see what fit is right for you once you’ve mastered it. Figure out your data needs, what you like to work with, and build a web scraper that runs like a well-oiled machine.

The information contained within this article, including information posted by official staff, guest-submitted material, message board postings, or other third-party material is presented solely for the purposes of education and furtherance of the knowledge of the reader. All trademarks used in this publication are hereby acknowledged as the property of their respective owners.

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