How to check programatically if url of page is redirecting?

Question

I am trying to extract the content of a webpage A. Using groovy I've tried the following

......
String urlStr = "url-of-webpage-A"
String pageText = urlStr.toURL().text
//println pageText
.....

The above code retrieves the text of webPage A as long as it doesn't redirect to an other webpage B. If A redirects to B, the page content of webPage B is retrieved in the pageText variable. Is there a way to code and check if webPage A is redirecting to an other webpage (in groovy or java)?

PS: The above piece of code is not a part of server side logic. I am executing it on the client side within the scope of a desktop appilcation.

Answer 1

In Java you can use URL.openConnection() to get a HttpURLConnection (you'll need to cast). On this you can call setInstanceFollowRedirects(false).

Then you can use getResponseCode() and see if HTTP_MOVED_PERM (301), HTTP_MOVED_TEMP (302) or HTTP_SEE_OTHER (303). They all indicate redirection.

If you need to know where you're being redirected to, then you can use getHeaderField("Location") to get the location header.

Answer 2

In groovy, you could do what Joachim suggests by doing:

String location = "url-of-webpage-A"
boolean wasRedirected = false
String pageContent = null

while( location ) {
  new URL( location ).openConnection().with { con ->
    // We'll do redirects ourselves
    con.instanceFollowRedirects = false

    // Get the response code, and the location to jump to (in case of a redirect)
    location = con.getHeaderField( "Location" )
    if( !wasRedirected && location ) {
      wasRedirected = true
    }

    // Read the HTML and close the inputstream
    pageContent = con.inputStream.withReader { it.text }
  }
}

println "wasRedirected:$wasRedirected contentLength:${pageContent.length()}"

If you don't want to be redirected, and want the contents of the first page, you simply need to do:

String location = "url-of-webpage-A"
String pageContent = new URL( location ).openConnection().with { con ->
  // We'll do redirects ourselves
  con.instanceFollowRedirects = false

  // Get the location to jump to (in case of a redirect)
  location = con.getHeaderField( "Location" )

  // Read the HTML and close the inputstream
  con.inputStream.withReader { it.text }
}

if( location ) { 
  println "Page wanted to redirect to $location"
}
println "Content was:"
println pageContent