How to get content type of a given url inside Java

问题:

I want to know the content type of a given url input by the user inside my Javascript code. Actually, I have a drop-down list (html,csv,xls etc.) and I want to make it so when the user inputs an url, I want to detect the type of the content of the url and based on this type I want to set the value of my drop-down list (html,csv,xls etc.). I know, I can get the content type using Ruby like this :

require 'open-uri'
str = open('http://example.com')
str.content_type #=> "text/html"

or, also, I could use curl to get the content and then parse it to know the content type. But, I need to do this inside my Javascript code because of my need explained above. Any thought ?

EDIT_1 :

I tried this code in my javascript :

    $("#wiki_form_url").change(function(){
        $.ajax({
            type: "GET",
            url: "content.rb",
            data: {
//                input_url: $("#wiki_form_url").val()
            },
            dataType: "html"
        }).done(function (data) {
                    // `data` contains the content-type
                    alert('Success !!!');
                }).fail(function () {
                    alert("failed AJAX call");
                });
    });

I have a ruby script content.rb inside which I do :

require 'open-uri'

str = open('http://www.ofdp.org/benchmark_indices/25')
str.content_type

But, it does not seem to work. I am getting Ajax failure. May be it's because of url path of the script content.rb ? How should I specify a script path here ? (Relative or absolute)

回答1:

The same origin policy prevents you from using client side JavaScript to directly discover information about arbitrary URIs (URIs you control are a different story).

You'll need to get that information with another technology, such as your server side Ruby.

You could do this by simply submitting a form to the server and returning a new webpage to the browser.

If you don't want to leave the page, then you can pass the data using Ajax. There are no shortage of Ajax tutorials out there, here is a good one from MDN.

回答2:

Here's an example of an AJAX call:

$(document).ready(function () {
    $("#button_check").on("click", function () {
        $.ajax({
            type: "GET",
            url: "Your URL",
            data: {
                input_url: $("#textbox_id").val()
            },
            dataType: "html"
        }).done(function (data) {
            // `data` contains the content-type
            alert(data);
        }).fail(function () {
            alert("failed AJAX call");
        });
    });
});

Where your HTML is something like:

<input type="text" id="textbox_id" />
<input type="button" id="button_check" value="Submit" />

And your Ruby code would be something like:

require 'open-uri'
class TestController < ApplicationController
  def index
    req = open(params[:input_url])
    render :text => req.content_type
  end
end

I have never used RoR before, so I have no idea if this is right or works in the slightest. But it's what I could quickly conjure up when scrambling through several tutorials. It's simply the concept you seem to be looking for. You'll need to figure out how to map a URL to this method, and then update the AJAX option url to use that.

So in the Javascript code - in the done method, that means the whole AJAX request was successful and the data variable should contain the result from the Ruby code req.content_type.

回答3:

Atlast I could figure out the whole thing with the great help of @Ian. Here is my completed code : In javascript file :

    $("#wiki_form_url").change(function () {
        $.ajax({
            type: "GET",
            url: "/wiki_forms/content",
            data: {
                input_url: $("#wiki_form_url").val()
            },
            dataType: "text"
        }).done(function (data) {
                    // `data` contains the content-type
                    alert('Success');
                    console.log(data);
//                    alert(data);
                }).fail(function () {
                    alert("failed AJAX call");
                });
    });

Inside my wiki_forms controller I created a new method named content :

  def content 
    req = open(params[:input_url])
    render :text => req.content_type 
  end

Then added a new route in routes.rb file :

  get "/wiki_forms/content" => 'wiki_forms#content'

and used /wiki_forms/content as the ajax request url. And, everything is working nicely now.