“As a newbie, I built a web crawler and successfully extracted 20k data from Amazon website.”
Do you also want to know how to make a web crawler and create a database that eventually turns into your asset at no cost? It’s not a difficult thing after you’ve learned the right tool and method. This article will share 3 different ways to help you build a web crawler step by step.
Before the easy steps, you can learn about the definition of a web crawler and how it can help you.
What Is A Web Crawler
A web crawler is an internet bot that indexes the content of websites (read the detailed definition on Wikipedia). It can automatically extract target information and data from websites and export data into structured formats (list/table/database).
You can view a web crawler as a particular program designed to crawl websites in orientation and glean data. However, you are unable to get the URL address of all web pages within a website containing many web pages in advance. Thus, what concerns us is how to fetch all the HTML web pages from a website.
Normally, we could define an entry page: One web page contains URLs of other web pages, and then we could retrieve these URLs from the current page and add all of these affiliated URLs into the crawling queue. Next, we crawl another page and repeat the same process as the first one, recursively. Essentially, we could assume the crawling scheme is a depth-search or breadth-traversal. And as long as we could access the Internet and analyze the web page, we could crawl a website. Fortunately, most programming languages offer HTTP client libraries to crawl web pages, and we can even use regular expressions for HTML analysis.
Some Tips for Crawling
- Crawl Depth – How many clicks from the entry page do you want the crawler to traverse? In most cases, a depth of 5 is enough for crawling from most websites.
- Distributed Crawling – The crawler will attempt to crawl the pages at the same time.
- Pause – The length of time the crawler pauses before crawling to the next page.
- The faster you set the crawler, the harder it will be on the server (At least 5-10 seconds between page clicks).
- URL template – The template will determine which pages the crawler wants data from.
- Save log – A saved log will store which URLs were visited and which were converted into data. It is used for debugging and prevents crawling a visited site repeatedly.
Here is a video that explains the web crawler and the difference between web crawlers and web scrapers.
You may be curious about is web crawler legal or not, well, it depends. But generally speaking, it’s totally legal in most countries to crawl public data on a website.
Why Do You Need A Web Crawler
Imagine a world without Google Search. How long do you think it will take to get a recipe for chicken nuggets from the Internet? There are 2.5 quintillion bytes of data being created online each day. Without search engines like Google, it will be like looking for a needle in a haystack.
From Hackernoon by Ethan Jarrell
A search engine is a unique kind of web crawler that indexes websites and finds web pages for us. Besides search engines, you can also build a customized web crawler to help you achieve:
1. Content aggregation: It works to compile information on niche subjects from various resources into one single platform. As such, it is necessary to crawl popular websites to fuel your platform in time.
2. Sentiment analysis: It is also called opinion mining. As the name indicates, it is the process to analyze public attitudes toward one product or service. It requires a monotonic set of data to evaluate accurately. A web crawler can extract tweets, reviews, and comments for analysis.
3. Lead generation: Every business needs sales leads. That’s how they survive and prosper. Let’s say you plan to make a marketing campaign targeting a specific industry. You can scrape email, phone number, and public profiles from an exhibitor or attendee list of Trade Fairs, like attendees of the 2018 Legal Recruiting Summit.
Method 1: Build A Web Crawler with Coding Script
Writing scripts with computer languages is predominantly used by programmers. It can be as powerful as you create it to be. Here is an example of a snippet of bot code.
From Kashif Aziz
3 steps to create a web crawler using Python
Step 1: Send an HTTP request to the URL of the webpage. It responds to your request by returning the content of web pages.
Step 2: Parse the webpage. A parser will create a tree structure of the HTML as the webpages are intertwined and nested together. A tree structure will help the bot follow the paths that we created and navigate through to get the information.
Step 3: Using the Python library to search the parse tree.
Among the computer languages for a web crawler, Python is an easy-to-implement compared to PHP and Java. It still has a steep learning curve that prevents many non-tech professionals from using it. Even though it is an economic solution to write your own, it’s still not sustainable with regard to the extended learning cycle within a limited time frame.
Method 2: Use No-coding Web Crawler Tool for FREE
If you don’t want to learn to code, you can try to use web scraping tools on the market. Here we recommend Octoparse, which is a free web crawler maker and has no requirements for coding. Octoparse provides auto-detecting mode so that you can crawl data from a website almost automatically. Also, you can customize the crawling workflow by dragging and dropping.
3 steps to build a web crawler without coding
Step 1: Download Octoparse and copy a web page link
Download and install Octoparse on your device, and paste the target web page URL to the main panel. It will begin detecting automatically to build a crawler workflow, or you can select “Advanced Mode” to try more customized options.
Step 2: Customize the web crawler data fields
You can simply preview the data that is detected, and click the “Create workflow” button to set the crawler. You can customize the data field as you need by clicking the target data position with the tips. Octoparse supports setting up pagination by clicking the “Next Page” button so that the crawler can navigate through it.
Step 3: Run the web crawler to extract data and export into Excel files
Once you finish setting up the extraction fields, click the “Run” button to execute the crawler. You can download the data to local devices by Excel or CSV.
If you still have questions, move to the user guide to learn more details. Octoparse also provides Task Templates that cover over 30 websites for starters to grow comfortable at the beginning. These templates allow users to capture the data without task configuration and are extremely beginner-friendly.
Method 3: Choose Preset Data Crawler Template
If you only want to crawl a specific site for data quickly, you can try to use a preset data scraping template. These templates are designed for popular scraped sites and can be used from the web page, which means that you don’t need to download any software to your device. They’re very friendly for beginners as you just need to enter several parameters and start crawling data.
Try the Amazon product data scraping template below.
https://www.octoparse.com/template/amazon-product-details-scraper
Conclusion
Writing scripts can be painful as it has high initial and maintenance costs. No single web page is identical, and we need to write a script for every single site. It is not sustainable if you need to crawl many different websites. Besides, websites tend to change layouts and structures after some time. As a result, we have to debug and adjust the crawler accordingly. A free web crawler like Octoparse or data crawler templates is more practical for beginners with less effort.
