What is golang crawler

Golang crawler refers to a program written in golang. By simulating client requests, accessing designated websites, and analyzing and extracting the content of the website, it can automatically obtain data, analyze competing products, monitor websites, etc. It will be of great help. Learning golang crawler can not only improve your technical level, but also better cope with the growing information needs. Crawler technology is widely used in information capture, data mining, website monitoring, automated testing and other fields.

The operating environment of this tutorial: windows10 system, golang1.20.1 version, DELL G3 computer.

Nowadays, with the continuous development of Internet technology, web crawling has become a very important skill. As an emerging programming language, golang has been widely used. This article will introduce you to how to use golang crawler.

What is golang crawler?

golang crawler refers to a program written in golang, which simulates client requests, accesses specified websites, and performs operations on the content of the website. Analysis and Extraction. This crawler technology is widely used in information capture, data mining, website monitoring, automated testing and other fields.

Advantages of golang crawler

As a static compiled language, golang has the characteristics of fast compilation speed, strong concurrency capability, and high operating efficiency. This gives the golang crawler the advantages of fast speed, good stability, and high scalability.

golang crawler tools

Third-party libraries

golang has a wealth of third-party libraries that can easily perform HTTP requests, HTML parsing, and concurrency Processing and other operations. Some of the important third-party libraries include:

net/http: used to send HTTP requests and process HTTP responses; net/url: used to process URL strings; goquery: a jQuery-based HTML parser, used Used to quickly find and traverse elements in HTML documents; goroutines and channels: used to implement parallel crawling and data flow control. Framework

golang also has some specialized crawler frameworks, such as:

Colly: a fast, flexible, and intelligent crawler framework that supports XPath and regular expression matching methods, and integrates Multiple advanced features, such as domain name limitation, request filtering, request callback, cookie management, etc. Gocrawl: A highly customizable crawler framework that supports URL redirection, page caching, request queuing, link speed limiting and other features. It also provides a comprehensive event callback interface to facilitate secondary development by users.

Golang crawler implementation steps

Sending HTTP requests

In golang, sending HTTP requests is implemented based on the standard library net/http. By creating an http.Client object and using its Do method to send HTTP requests and receive responses. The following is sending HTTP Code example for GET request:

import (
"net/http"
"io/ioutil"
)
func main() {
resp, err := http.Get("http://example.com/")
if err != nil {
// 处理错误
}
defer resp.Body.Close()
body, err := ioutil.ReadAll(resp.Body)
if err != nil {
// 处理错误
}
// 处理返回的内容
}

Parsing HTML

In golang, parsing HTML is implemented based on the third-party library goquery. Using goquery, you can quickly find and traverse HTML elements through CSS selectors and other methods. The following is a code example for parsing HTML:

import (
"github.com/PuerkitoBio/goquery"
"strings"
)
func main() {
html := `
Link 1
Link 2
Link 3
`
doc, err := goquery.NewDocumentFromReader(strings.NewReader(html))
if err != nil {
// 处理错误
}
doc.Find("ul li a").Each(func(i int, s *goquery.Selection) {
// 处理每个a标签
href, _ := s.Attr("href")
text := s.Text()
})
}

Parallel processing

Golang, as a concurrent programming language, has excellent parallel capabilities. In crawlers, parallel processing of multiple requests can be achieved through goroutines and channels. The following is a code example of parallel processing:

import (
"net/http"
"io/ioutil"
"fmt"
)
func fetch(url string, ch chan<- string) {
resp, err := http.Get(url)
if err != nil {
ch <- fmt.Sprintf("%s: %v", url, err)
return
}
defer resp.Body.Close()
body, err := ioutil.ReadAll(resp.Body)
if err != nil {
ch <- fmt.Sprintf("%s: %v", url, err)
return
}
ch <- fmt.Sprintf("%s: %s", url, body)
}
func main() {
urls := []string{"http://example.com/1", "http://example.com/2", 
"http://example.com/3"}
ch := make(chan string)
for _, url := range urls {
go fetch(url, ch)
}
for range urls {
fmt.Println(<-ch)
}
}

Summary

golang crawler is a very promising skill that can bring great benefits to us in automating data acquisition, analyzing competitive products, monitoring websites, etc. s help. Learning golang crawler can not only improve our technical level, but also allow us to better cope with the growing information needs.

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