How to crawl golang

Golang is a very popular backend programming language that can be used to complete many tasks, one of which is crawling. This article will introduce how to use Golang to write a simple crawler program.

1. Preparation

Before starting to write a crawler, we need to install a Golang web crawler framework called GoScrape. Before using it, we need to install GoScrape first:

go get github.com/yhat/scrape

2. Implementing the crawler

Before implementing the crawler, we need to first determine the goal of the crawler. In this example, we will use Golang to crawl questions related to "Golang" on Zhihu.

First, we need to define a function to send a request to the Zhihu server and obtain the page content. The following code implements a simple function to get the page content:

func getPageContent(url string) ([]byte, error) {
    res, err := http.Get(url)
    if err != nil {
        return nil, err
    }
    defer res.Body.Close()

    body, err := ioutil.ReadAll(res.Body)
    if err != nil {
        return nil, err
    }

    return body, nil
}

This function uses Go's standard libraries "net/http" and "io/ioutil" to perform requests and read responses. After processing is complete, it returns the contents of the response and an error object so that we can get help when handling the error.

Next, we need to process the crawled page content. In this example, we will use GoScrape to parse HTML and extract the information we need. Here is a function to parse the page content:

func extractData(content []byte) {
    root, err := html.Parse(bytes.NewReader(content))
    if err != nil {
        panic(err)
    }

    matcher := func(n *html.Node) bool {
        if n.Type == html.ElementNode && n.Data == "a" {
            for _, attr := range n.Attr {
                if attr.Key == "class" && attr.Val == "question_link" {
                    return true
                }
            }
        }
        return false
    }

    questions := scrape.FindAll(root, matcher)

    for _, q := range questions {
        fmt.Println(scrape.Text(q))
    }
}

This function uses "golang.org/x/net/html" to parse the HTML and uses GoScrape to find the HTML elements in the page that are relevant to the question we need. In this example, we will use the "a" tag and the class name "question_link" as the matcher. If used correctly, this matcher will return HTML elements containing all problematic connections. Finally we will extract them using GoScrape's text extraction feature. Finally output the title of the problem to the console.

Finally, we combine these two functions so that they can be executed continuously. The following code demonstrates how to use these functions to crawl Zhihu:

func main() {
    url := "https://www.zhihu.com/search?type=content&q=golang"

    content, err := getPageContent(url)
    if err != nil {
        panic(err)
    }

    extractData(content)
}

Here we define a "main" function to integrate the two previously mentioned functions. First, we call the “getPageContent” function to obtain Zhihu’s search results page. If any error occurs, we will exit the program, otherwise we will pass the return result to the "extractData" function, which will parse the page content and extract the title of the question, and finally output it to the console.

3. Summary

This article introduces how to use Golang to write a simple crawler program. We learned how to use GoScrape and the standard library to fetch and process HTML content with step-by-step explanations. In practice, these concepts can be extended and optimized to achieve more complex crawler behavior.

The above is the detailed content of How to crawl golang. For more information, please follow other related articles on the PHP Chinese website!