第一篇随笔:用VB.NET搞点简单事情(1)

网络上能搜索到的爬虫文章大多是用python做的,也有少部分是C#做的(小声:所以用VB.NET也可以做爬虫.本文写的是第一步:获取网页)

使用代码前先imports以下内容

Imports System.IO, System.IO.Compression, System.Text, System.Net

写程序前先开浏览器(我用的Chrome),随便上个网页,F12看下header,粘下来useragent备用,也可以粘下accept,cookie等(在本文中用不到

用httpwebrequest建立请求,用httpwebresponse得到响应体.然后考虑下压缩的问题(imports System.IO.Compression就是解决这个的)

最后得到真正的返回流,streamreader读取之,然后网页的http代码就搞下来了.用这种方法可以搞定编码为UTF-8的网页对于编码是GB2312或GBK的需有改动:使用streamreader时第二个参数改为Encoding.GetEncoding("gbk")

下面是代码:

Public Function GetHttpContent(url As String) As String
        Try
            Dim req As HttpWebRequest = HttpWebRequest.CreateHttp(url), resp As HttpWebResponse, sol$
            With req
                .UserAgent = "Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/74.0.3729.169 Safari/537.36"
                .Accept = "*/*"
                .Method = "GET"
                .Timeout = 300000
                .Headers.Add("accept-encoding", " gzip, deflate")
            End With
            resp = req.GetResponse
            Select Case resp.ContentEncoding.ToLower
                Case "gzip"
                    Using z As New GZipStream(resp.GetResponseStream, CompressionMode.Decompress)
                        Using sr As New StreamReader(z, Encoding.UTF8)
                            sol = sr.ReadToEnd
                        End Using
                    End Using
                    Exit Select
                Case "deflate"
                    Using z As New DeflateStream(resp.GetResponseStream, CompressionMode.Decompress)
                        Using sr As New StreamReader(z, Encoding.UTF8)
                            sol = sr.ReadToEnd
                        End Using
                    End Using
                    Exit Select
                Case Else
                    Using sr As New StreamReader(resp.GetResponseStream, Encoding.UTF8)
                        sol = sr.ReadToEnd
                    End Using
                    Exit Select
            End Select
            Return sol
        Catch ex As Exception
            Return ""
        End Try
    End Function

(本人水平有限,代码有不完善的地方欢迎指出