检查Cookie是否存在

Question

From a quick search on Stack Overflow I saw people suggesting the following way of checking if a cookie exists:

HttpContext.Current.Response.Cookies["cookie_name"] != null

or (inside a Page class):

this.Response.Cookies["cookie_name"] != null

However, when I try to use the indexer (or the Cookies.Get method) to retrieve a cookie that does not exist it seems to actually create a 'default' cookie with that name and return that, thus no matter what cookie name I use it never returns null. (and even worse - creates an unwanted cookie)

Am I doing something wrong here, or is there a different way of simply checking for the existance of a specific cookie by name?

Answer 1

Sometimes you still need to know if Cookie exists in Response. Then you can check if cookie key exists:

HttpContext.Current.Response.Cookies.AllKeys.Contains("myCookie")

More info can be found here .

In my case I had to modify Response Cookie in Application_EndRequest method in Global.asax. If Cookie doesn't exist I don't touch it:

string name = "myCookie";
HttpContext context = ((HttpApplication)sender).Context;
HttpCookie cookie = null;

if (context.Response.Cookies.AllKeys.Contains(name))
{
    cookie = context.Response.Cookies[name];
}

if (cookie != null)
{
    // update response cookie
}

Answer 2

There are a lot of right answers here depending on what you are trying to accomplish; here's my attempt at providing a comprehensive answer:

Both the Request and Response objects contain Cookies properties, which are HttpCookieCollection objects.

Request.Cookies:

• This collection contains cookies received from the client
• This collection is read-only
• If you attempt to access a non-existent cookie from this collection, you will receive a null value.

Response.Cookies:

• This collection contains only cookies that have been added by the server during the current request.
• This collection is writeable
• If you attempt to access a non-existent cookie from this collection, you will receive a new cookie object; If the cookie that you attempted to access DOES NOT exist in the Request.Cookies collection, it will be added (but if the Request.Cookies object already contains a cookie with the same key, and even if it's value is stale, it will not be updated to reflect the changes from the newly-created cookie in the Response.Cookies collection.

Solutions

---

If you want to check for the existence of a cookie from the client, do one of the following

• Request.Cookies["COOKIE_KEY"] != null
• Request.Cookies.Get("COOKIE_KEY") != null
• Request.Cookies.AllKeys.Contains("COOKIE_KEY")

---

If you want to check for the existence of a cookie that has been added by the server during the current request , do the following:

• Response.Cookies.AllKeys.Contains("COOKIE_KEY") (see here )

Attempting to check for a cookie that has been added by the server during the current request by one of these methods...

• Response.Cookies["COOKIE_KEY"] != null
• Response.Cookies.Get("COOKIE_KEY") != null (see here )

...will result in the creation of a cookie in the Response.Cookies collection and the state will evaluate to true .

Answer 3

You need to use HttpContext.Current.Request.Cookies , not Response.Cookies .

Side note: cookies are copied to Request on Response.Cookies.Add , which makes check on either of them to behave the same for newly added cookies. But incoming cookies are never reflected in Response .

This behavior is documented in HttpResponse.Cookies property:

After you add a cookie by using the HttpResponse.Cookies collection, the cookie is immediately available in the HttpRequest.Cookies collection, even if the response has not been sent to the client.

Answer 4

Response.Cookies contains the cookies that will be sent back to the browser. If you want to know whether a cookie exists, you should probably look into Request.Cookies .

Anyway, to see if a cookie exists, you can check Cookies.Get(string) . However, if you use this method on the Response object and the cookie doesn't exist, then that cookie will be created.

See MSDN Reference for HttpCookieCollection.Get Method (String)

Answer 5

public static class CookieHelper
{
    /// <summary>
    /// Checks whether a cookie exists.
    /// </summary>
    /// <param name="cookieCollection">A CookieCollection, such as Response.Cookies.</param>
    /// <param name="name">The cookie name to delete.</param>
    /// <returns>A bool indicating whether a cookie exists.</returns>
    public static bool Exists(this HttpCookieCollection cookieCollection, string name)
    {
        if (cookieCollection == null)
        {
            throw new ArgumentNullException("cookieCollection");
        }

        return cookieCollection[name] != null;
    }
}

Usage:

Request.Cookies.Exists("MyCookie")

Answer 6

Sorry, not enough rep to add a comment, but from zmbq's answer:

Anyway, to see if a cookie exists, you can check Cookies.Get(string), this will not modify the cookie collection.

is maybe not fully correct, as Cookies.Get(string) will actually create a cookie with that name, if it does not already exist. However, as he said, you need to be looking at Request.Cookies, not Response.Cookies So, something like:

bool cookieExists = HttpContext.Current.Request.Cookies["cookie_name"] != null;

Answer 7

你可以做这样的事情来找出cookies的价值：

Request.Cookies[SESSION_COOKIE_NAME].Value