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This article mainly introduces the use of Cookies in Jsp, has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, the following let the editor take you to understand it.

1. Cookie is added to the Set-Cookie response header through HttpServletResponse's addCookie method.

For example:

Cookie userCookie = new Cookie ("user", "admin"); response.addCookie (userCookie)

There are two important methods that are related to setup.

1.setMaxAge

Sets the time, in seconds, before the Cookie expires. If you do not set this value, the Cookie is valid only within the current session, and these Cookie are not saved to disk.

Note: deleting cookie is achieved through this method. The deletion of the cookie can be achieved by specifying a time of 0 before the expiration of the cookie to be deleted.

2.setPath

Sets the path that Cookie applies to. If you do not specify a path, Cookie will return to all pages under the directory where the current page (jsp (* for SUN enterprise applications) or Servlet mapping) is located and its subdirectories.

Note:

A: all cookie have paths

B: the path set by this method is the client path, that is, "/" represents the server root directory, not the WEB application root directory.

C: when setting the path in this method, "/ myWeb/" is different from "/ myWeb"; the former can be associated to the server's myWeb directory, while the latter cannot.

D: when this method sets the path, there is no relative directory to speak of, that is, no matter which directory you set setPath ("/ myWeb/"), the cookie will be associated to the server's myWeb directory (setPath ("/ myWeb") is not allowed), rather than a subdirectory of the myWeb of the current directory; similarly, setting setPath ("myWeb/") and setPath ("myWeb") cannot be associated to the subdirectory of the myWeb of the current directory.

Here is a strange example, that is, the cookie set under one web application can be obtained under another web application (both web applications are on the same server)

Directory structure: there are web1 and web2 directories on the server root directory, setcookie.jsp (SUN enterprise applications * *) and getcookie.jsp (SUN enterprise applications * *) under web1, and getcookie.jsp (SUN enterprise applications *) under web2

Setcookie.jsp under web1 (* for SUN enterprise applications)

Getcookie.jsp under web1 (* for SUN enterprise applications)

Getcookie.jsp under web2 (* for SUN enterprise applications)

First visit setcookie.jsp under web1 (* for SUN enterprise applications), and then visit the getcookie.jsp (* for SUN enterprise applications) files under web1 and web2 respectively. You will find a strange phenomenon. In getcookie.jsp (* for SUN enterprise applications) under web1, user is empty, while in getcookie.jsp (* for SUN enterprise applications), user is valuable. This enables the cookie set from one web application to be obtained under another web application.

Most people do not succeed in deleting cookie because of directory reasons. A typical reason is to set cookie in one directory (without calling the setPath method) but delete the cookie in another directory (actually calling the setMaxAge method)

3. The method of sharing cookie across domains: setting

Cookie.setDomain (".jszx.com")

Domain where computer An is located: home.langchao.com,A has application cas

Domain where the B machine is located: jszx.com,B has application webapp_b

1) when you set cookie under cas, add cookie.setDomain (".jszx.com"); so that you can get cookie under webapp_b.

2) this parameter must be "." Start.

3) when entering url to access webapp_b, you must enter a domain name before it can be resolved. For example, if you enter: http://lc-bsp.jszx.com:8080/webapp_b, on A machine, you can get the cookie set by cas on the client side, while B machine accesses the local application, and typing: http://localhost:8080/webapp_b does not get cookie.

4) cookie.setDomain (".jszx.com") is set, and can also be shared under the default home.langchao.com.

Second, read

The getCookies method of HttpServletRequest is called when the Cookie is read from the client. This method returns an array of Cookie objects corresponding to the contents in the HTTP request header. After you get this array, you usually iterate through the elements and call getName to check the names of each Cookie until you find the target Cookie. Then call getValue on the target Cookie and do other processing based on the results obtained.

Note: if the parent directory of jsp (* * of SUN enterprise applications) and Servlet (Servlet is its mapping directory) has the same name cookie, then the Cookie array obtained by the request.getCookie () method holds the information of cookie in its parent directory.

III. Explanation

We know that for request and response in a page, it is generated by a http request, and request is all the parameters in the http request, so it contains the value of cookie when issuing this http request, and response is the response to this http request webapplication, so it can write the value of cookie. From this point of view, the value of cookie obtained by request is completely different from the value of cookie to be written by response.

To put it simply, the value of cookie obtained by request is the value of cookie before this http request, while the value of response is the value of cookie after this http request. Therefore, in the same request and response, if a new cookie,request is added to the response, it is not available.

Thank you for reading this article carefully. I hope the article "what is the use of Cookies in Jsp" shared by the editor will be helpful to you. At the same time, I also hope you will support us and pay attention to the industry information channel. More related knowledge is waiting for you to learn!

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