- Web scraping with Java using Webmagic Webmagic is an open-source, scalable crawler framework developed by code craft. The framework boasts developer support of 40+ contributors — the developers based this framework on Scrapy architecture, the python scraping library. Moreover, the team has based several features on Jsoup library.
- The basic idea of web scraping is that we are taking existing HTML data, using a web scraper to identify the data, and convert it into a useful format. The end stage is to have this data stored as either JSON, or in another useful format.
- See full list on scrapingbee.com.
Apache Nutch is one of the most efficient and popular open source web crawler. CloudflareIuamSolver is the Java library for breaking through the Cloudflare's 'I am Under Attack Mode'. Webscraper scrapy-spider webscraping scrapy-crawler.
8 Most Popular Java Web Crawling & Scraping Libraries
Article originally posted on Data Science Central. Visit Data Science Central
Introduction :
Web scraping or crawling is the process of extracting data from any website. The data does not necessarily have to be in the form of text, it could be images, tables, audio or video. It requires downloading and parsing the HTML code in order to scrape the data that you require.
Since data is growing at a fast clip on the web, it is not possible to manually copy and paste it. At times, it is not possible for technical reasons. In any case, web scraping and crawling enables this process of fetching the data in an easy and automated fashion. As it is automated, there’s no upper limit to how much data you can extract. In other words, you can extract large quantities of data from disparate sources.
Data has always been important but of late, businesses have begun to use data in order to make business decisions. As businesses rely heavily on data for decision making, web scraping has, in turn, grown in significance. However, as data needs to be collated from different sources, it is even more important to leverage web scraping as it can make this entire exercise quite easy and hassle-free.
As information is scattered all over the digital space in the form of news, social media posts, images on Instagram, articles, e-commerce sites etc., web scraping is the most efficient way to keep an eye on the big picture and derive business insights that can propel your enterprise. In this context, java web scraping/crawling libraries can come in quite handy. Here’s a list of best java web scraping/crawling libraries which can help you to crawl and scrape the data you want from the Internet.
1. Apache Nutch
Apache Nutch is one of the most efficient and popular open source web crawler software projects. It’s great to use because it offers varied extensible interfaces such as Parse, Index and Scoring Filter’s custom implementations such as Apache Tika for parsing. Moreover, it is also possible to use pluggable indexing for Apache Solr, Elastic Search etc.
Pros:
- Highly scalable and relatively feature rich crawler.
- Features like politeness, which obeys robots.txt rules.
- Robust and scalable – Nutch can run on a cluster of up to 100 machines.
Resources:
- Learn More:Apache Nutch – Step by Step
2. StormCrawler
StormCrawler stands out as it serves a library and collection of resources that developers can use for building their own crawlers. StormCrawler is also preferred by many for use cases in which the URL to fetch and parse come as streams. However, you can also use it for large scale recursive crawls particularly where low latency is needed.
Pros:
- scalable
- resilient
- low latency
- easy to extend
- polite yet efficient
Resources:
- Learn More:Getting Started with StormCrawler
3. Jsoup
jsoupis great as a Java library which helps you navigate the real-world HTML. Developers love it because offers quite a convenient API for extracting and manipulating data, making use of the best of DOM, CSS and jquery-like methods.
Pros:
- Fully supports CSS selectors
- Sanitize HTML
- Built-in proxy support
- Provides a slick API to traverse the HTML DOM tree to get the elements of interest.
Resources:
- Learn More:Jsoup HTML parser – Tutorial & examples
4. Jaunt
Jauntis a unique Java library that helps you in processes pertaining to web scraping, web automation and JSON querying. When it comes to a browser, it does provide web scraping functionality, access to DOM, and control over each HTTP Request/Response but does not support JavaScript. Since Jaunt is a commercial library, it offers diverse kinds of versions, paid as well as free for a monthly download.
Pros:
- The library provides a fast, ultra-light headless browser
- Web pagination discovery
- Customizable caching & content handlers
Resources :
- Learn More:Jaunt Web Scraping Tutorial – Quickstart
5. Norconex HTTP Collector
If you are looking for open source web crawlers related to enterprise needs, Norconex is what you need.
Norconexis a great tool because it enables you to crawl any kind of web content that you need. You can use it as you wish- as a full-featured collector or embed it in your own application. Moreover, it works well on any operating system. It can crawl millions of pages on a single server of median capacity.
Pros:
- Highly scalable – Can crawl millions on a single server of average capacity
- OCR support on images and PDFs
- Configurable crawling speed
- Language detection
Resources:
Web Scraper Javascript Python
- DownloadNorconex HTTP Collector
- Learn More:Getting Started with Norconex HTTP Collector
6. WebSPHINX
WebSPHINX(Website-Specific Processors for HTML INformation eXtraction) is an excellent tool as a Java class library and interactive development environment for web crawlers. WebSPHINX comprises two main parts: the Crawler Workbench and the WebSPHINX class library.
Pros:
- Provide a graphical user interface that lets you configure and control a customizable web crawler
Resources:
- Learn More:Crawling web pages with WebSPHINX
7. HtmlUnit
HtmlUnitis a headless web browser written in Java.
It’s a great tool because it allows high-level manipulation of websites from other Java code, including filling and submitting forms and clicking hyperlinks.
It has also got considerable JavaScript support which continues to improve. It is also equipped to work even with the most complex AJAX libraries, simulating Chrome, Firefox or Internet Explorer depending on the configuration used. It is mostly made use of when it comes to testing purposes in order to fetch information from websites.
Pros:
- Provides high-level API, taking away lower-level details away from the user.
- It can be configured to simulate a specific Browser.
Resources:
- Learn More:Web Scraping with Java and HtmlUnit
8. Gecco
Geccois also a hassle-free lightweight web crawler developed with Java language. Gecco framework is preferred for its remarkable scalability. The framework is based on the principle of open and close design, the provision to modify the closure and the expansion of open.
Pros:
- Support for asynchronous Ajax requests in the page
- Support the download proxy server randomly selected
- Using Redis to realize distributed crawling
Resources:
- Learn More:Teach you to use java crawler gecco to grab all JD product information (1)
Conclusion :
As the applications of web scraping grow, the use of Java web scraping libraries is also set to accelerate. Since there are various libraries, and each one has its own unique features, it will require some study on the part of the end user. However, it will also depend on the respective needs of different end users which will determine which tool would suit better. Once the needs are clear, it would be possible to leverage these tools and power your web scraping endeavours in order to gain a competitive advantage!
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A year or two after I created the dead simple web crawler in Python, I was curious how many lines of code and classes would be required to write it in Java. It turns out I was able to do it in about 150 lines of code spread over two classes. That's it!
How does it work?
You give it a URL to a web page and word to search for. The spider will go to that web page and collect all of the words on the page as well as all of the URLs on the page. If the word isn't found on that page, it will go to the next page and repeat. Pretty simple, right? There are a few small edge cases we need to take care of, like handling HTTP errors, or retrieving something from the web that isn't HTML, and avoid accidentally visiting pages we've already visited, but those turn out to be pretty simple to implement. I'll show you how.
I'll be using Eclipse along the way, but any editor will suffice. There are only two classes, so even a text editor and a command line will work.
Let's fire up Eclipse and start a new workspace.
We'll create a new project.
And finally create our first class that we'll call Spider.java.
We're almost ready to write some code. But first, let's think how we'll separate out the logic and decide which classes are going to do what. Let's think of all the things we need to do:
- Retrieve a web page (we'll call it a document) from a website
- Collect all the links on that document
- Collect all the words on that document
- See if the word we're looking for is contained in the list of words
- Visit the next link
Is that everything? What if we start at Page A and find that it contains links to Page B and Page C. That's fine, we'll go to Page B next if we don't find the word we're looking for on Page A. But what if Page B contains a bunch more links to other pages, and one of those pages links back to Page A?
We'll end up back at the beginning again! So let's add a few more things our crawler needs to do:
- Keep track of pages that we've already visited
- Put a limit on the number of pages to search so this doesn't run for eternity.
Let's sketch out the first draft of our Spider.java class:
Why is pagesVisited a Set? Remember that a set, by definition, contains unique entries. In other words, no duplicates. All the pages we visit will be unique (or at least their URL will be unique). We can enforce this idea by choosing the right data structure, in this case a set.
Why is pagesToVisit a List? This is just storing a bunch of URLs we have to visit next. When the crawler visits a page it collects all the URLs on that page and we just append them to this list. Recall that Lists have special methods that Sets ordinarily do not, such as adding an entry to the end of a list or adding an entry to the beginning of a list. Every time our crawler visits a webpage, we want to collect all the URLs on that page and add them to the end of our big list of pages to visit. Is this necessary? No. But it makes our crawler a little more consistent, in that it'll always crawl sites in a breadth-first approach (as opposed to a depth-first approach).
Remember how we don't want to visit the same page twice? Assuming we have values in these two data structures, can you think of a way to determine the next site to visit?
...
Okay, here's my method for the Spider.java class:
A little explanation: We get the first entry from pagesToVisit, make sure that URL isn't in our set of URLs we visited, and then return it. If for some reason we've already visited the URL (meaning it's in our set pagesVisited) we keep looping through the list of pagesToVisit and returning the next URL.
Okay, so we can determine the next URL to visit, but then what? We still have to do all the work of HTTP requests, parsing the document, and collecting words and links. But let's leave that for another class and wrap this one up. This is an idea of separating out functionality. Let's assume that we'll write another class (we'll call it SpiderLeg.java) to do that work and this other class provides three public methods:
Assuming we have this other class that's going to do the work listed above, can we write one public method for this Spider.java class? What are our inputs? A word to look for and a starting URL. Let's flesh out that method for the Spider.java class:
That should do the trick. We use all of our three fields in the Spider class as well as our private method to get the next URL. We assume the other class, SpiderLeg, is going to do the work of making HTTP requests and handling responses, as well as parsing the document. This separation of concerns is a big deal for many reasons, but the gist of it is that it makes code more readable, maintainable, testable, and flexible.
Let's look at our complete Spider.java class, with some added comments and javadoc:
}
Okay, one class down, one more to go. Earlier we decided on three public methods that the SpiderLeg class was going to perform. The first was public void crawl(nextURL) that would make an HTTP request for the next URL, retrieve the document, and collect all the text on the document and all of the links or URLs on the document. Unfortunately Java doesn't come with all of the tools to make an HTTP request and parse the page in a super easy way. Fortunately there's a really lightweight and super easy to use package called jsoup that makes this very easy. There's about 700 lines of code to form the HTTP request and the response, and a few thousand lines of code to parse the response. But because this is all neatly bundled up in this package for us, we just have to write a few lines of code ourselves.
For example, here's three lines of code to make an HTTP request, parse the resulting HTML document, and get all of the links:
That could even be condensed into one line of code if we really wanted to. jsoup is a really awesome project. But how do we start using jsoup?
You import the jsoup jar into your project!
Okay, now that we have access to the jsoup jar, let's get back to our crawler. Let's start with the most basic task of making an HTTP request and collecting the links. Later we'll improve this method to handle unexpected HTTP response codes and non HTML pages.
First let's add two private fields to this SpiderLeg.java class:
And now the simple method in the SpiderLeg class that we'll later improve upon
Still following? Nothing too fancy going on here. There are two little tricks in that we have to know how to specify all the URLs on a page such as a[href] and that we want the absolute URL to add to our list of URLs.
Great, and if we remember the other thing we wanted this second class (SpiderLeg.java) to do, it was to search for a word. This turns out to be surprisingly easy:
We'll also improve upon this method later.
Okay, so this second class (SpiderLeg.java) was supposed to do three things:
- Crawl the page (make an HTTP request and parse the page)
- Search for a word
- Return all the links on the page
We've just written methods for the first two actions. Remember that we store the links in a private field in the first method? It's these lines:
So to return all the links on the page we just provide a getter to this field
Done!
Okay, let's look at this code in all its glory. You'll notice I added a few more lines to handle some edge cases and do some defensive coding. Here's the complete SpiderLeg.java class:
Why the USER_AGENT? This is because some web servers get confused when robots visit their page. Some web servers return pages that are formatted for mobile devices if your user agent says that you're requesting the web page from a mobile web browser. If you're on a desktop web browser you get the page formatted for a large screen. If you don't have a user agent, or your user agent is not familiar, some websites won't give you the web page at all! This is rather unfortunate, and just to prevent any troubles, we'll set our user agent to that of Mozilla Firefox.
Ready to try out the crawler? Remember that we wrote the Spider.java class and the SpiderLeg.java class. Inside the Spider.java class we instantiate a spiderLeg object which does all the work of crawling the site. But where do we instantiate a spider object? We can write a simple test class (SpiderTest.java) and method to do this.
Further Reading
My original how-to article on making a web crawler in 50 lines of Python 3 was written in 2011. I also wrote a guide on making a web crawler in Node.js / Javascript. Check those out if you're interested in seeing how to do this in another language.
If Java is your thing, a book is a great investment, such as the following.
I know that the Effective Java book is pretty much required reading at a lot of tech companies using Java (such as Amazon and Google). Joshua Bloch is kind of a big deal in the Java world.
Good luck!