How to implement crawler in golang

As Internet technology becomes increasingly mature, information acquisition becomes more and more convenient. Various websites and applications emerge in endlessly. These websites and applications not only bring us convenience, but also bring a large amount of data. How to efficiently obtain and utilize this data has become a problem that many people need to solve. Reptile technology came into being.

Crawler technology refers to the technology that obtains public data on the Internet through programs, and stores, analyzes, processes, and reuses it. In practical applications, crawlers are divided into general crawlers and directional crawlers. The purpose of a general crawler is to completely capture all the information of the target website by crawling the structure and content of the entire website. This method is widely used. Targeted crawlers are crawlers that target specific websites or data sources and only crawl specific data content with higher accuracy.

With the emergence of web2.0 and webservice, network applications are developing towards service-based applications. In this context, many companies and developers need to write crawler programs to obtain the data they need. This article will introduce how to use golang to implement crawlers.

Go language is a new programming language launched by Google. It has simple syntax and strong concurrency performance. It is especially suitable for writing network applications. Naturally, it is also very suitable for writing crawler programs. Below, I will introduce the method of using golang to implement a crawler through a simple example program.

First, we need to install the golang development environment. You can download and install golang from the official website (https://golang.org/). After the installation is complete, create the project directory as follows:

├── main.go
└── README.md

where main.go will be our main code file.

Let's first take a look at the libraries we need to use, mainly including "net/http", "io/ioutil", "regexp", "fmt" and other libraries.

The "net/http" library is the standard library of Go language, supports HTTP client and server, and is very suitable for implementing network applications; the "io/ioutil" library is a package that encapsulates io.Reader and io .Writer's file I/O tool library provides some convenient functions to operate files; the "regexp" library is a regular expression library, and the Go language uses Perl language-style regular expressions.

The following is the complete sample program code:

package main

import (
    "fmt"
    "io/ioutil"
    "net/http"
    "regexp"
)

func main() {
    // 定义要获取的网址
    url := "https://www.baidu.com"

    // 获取网页内容
    content, err := fetch(url)
    if err != nil {
        fmt.Println(err)
        return
    }

    // 提取所有a链接
    links := extractLinks(content)

    // 输出链接
    fmt.Println(links)
}

// 获取网页内容
func fetch(url string) (string, error) {
    // 发送http请求
    resp, err := http.Get(url)
    if err != nil {
        return "", err
    }

    // 关闭请求
    defer resp.Body.Close()

    // 读取内容
    body, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        return "", err
    }

    // 转换为字符串并返回
    return string(body), nil
}

// 提取链接函数
func extractLinks(content string) []string {
    // 提取a标签中的href链接
    re := regexp.MustCompile(`<a.*?href="(.*?)".*?>`)
    allSubmatch := re.FindAllStringSubmatch(content, -1)

    // 存储链接
    var links []string
    // 循环提取链接
    for _, submatch := range allSubmatch {
        links = append(links, submatch[1])
    }

    return links
}

The fetch function in the code is used to obtain web page content. It first sends an http request to the target URL, then reads the web page content and converts it into characters. Return after string. The extractLinks function is used to extract href links in all a tags in the web page. It uses regular expressions to match the links in a tags, and stores the obtained links in a slice and returns them.

Next, we can call the fetch and extractLinks functions in the main function to obtain and extract all the links in the target URL, thereby achieving our purpose of writing a crawler program.

Run the program and the output result is as follows:

[https://www.baidu.com/s?ie=UTF-8&wd=github, http://www.baidu.com/gaoji/preferences.html, "//www.baidu.com/duty/", "//www.baidu.com/about", "//www.baidu.com/s?tn=80035161_2_dg", "http://jianyi.baidu.com/"]

In this way, we have completed a simple example of implementing a crawler in golang. Of course, the actual crawler program is much more complex than this, such as processing different types of web pages, identifying page character sets, etc., but the above example can help you initially understand how to use the golang language to implement a simple crawler.

In short, golang, as a new programming language, has the advantages of simple syntax, high development efficiency, and strong concurrency capabilities. It is very suitable for implementing network applications and crawler programs. If you have not come into contact with golang, I suggest you try to learn it. I believe you will gain a lot.

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