使用R提取ASPX页面船舶数据的技术咨询

Hey there! Since you already know standard web scraping methods, let's focus on the unique quirks of ASPX pages here—they rely on hidden form fields and POST requests to handle dynamic actions like clicking that "information" button without changing the URL. Here's a step-by-step approach to pull all the ship details:

1. Inspect the Request with Browser Dev Tools #

First, we need to uncover what happens behind the scenes when you click an "information" button:

• Open your browser's developer tools (press F12), go to the Network tab, and check the "Preserve log" option.
• Click any "information" button on the table. You'll see a new POST request show up (it still targets the same table.aspx URL).
• Click into that POST request, then look at the Form Data section. You'll notice ASPX-specific fields like:
  • __VIEWSTATE: A hidden value the page uses to track user session state
  • __VIEWSTATEGENERATOR & __EVENTVALIDATION: Security tokens the server uses to validate requests
  • __EVENTTARGET & __EVENTARGUMENT: These tell the server exactly which button you clicked (e.g., the unique identifier for that row's "information" button)

2. Extract Initial Hidden Fields #

Before simulating a button click, you need to grab those critical hidden values from the original page:

• Send a GET request to the initial table.aspx URL to fetch the page HTML.
• Parse the HTML to extract the values of __VIEWSTATE, __VIEWSTATEGENERATOR, and __EVENTVALIDATION (libraries like BeautifulSoup in Python make this easy—just locate the hidden input tags by their name attributes).

3. Simulate the POST Request for Each Ship #

For every row in the table:

• Find the unique identifier for that row's "information" button. Check the button's HTML via dev tools—it might have a name attribute like ctl00$ContentPlaceHolder1$gvOSIRIS$ctl02$btnInfo (the ctl02 part changes per row).
• Construct the POST request's Form Data with:
  • All the hidden fields you extracted earlier
  • The __EVENTTARGET set to the button's name value (some pages use __EVENTARGUMENT to pass row identifiers instead)
• Send the POST request to the same table.aspx URL. Use a session object (like requests.Session() in Python) to automatically handle cookies and maintain your session across requests—this avoids being blocked or logged out.
• Parse the response HTML to extract the ship details from the resulting page.

4. Loop Through All Rows #

Repeat steps 2-3 for every row in the initial table. A few pro tips to make this smoother:

• Refresh the hidden fields (__VIEWSTATE, etc.) before each request—some ASPX pages invalidate these tokens after every action, so re-fetching them ensures your requests are valid.
• Add a small delay between requests (1-2 seconds) to avoid overwhelming the server—always respect the website's terms of service.

内容的提问来源于stack exchange，提问作者Kumpelka