Advanced Internet Technology Lab # 6

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1 Faculty of Engineering Computer Engineering Department Islamic University of Gaza 2011 Advanced Internet Technology Lab # 6 JSP cookies Eng. Doaa Abu Jabal

2 Advanced Internet Technology Lab # 6 JSP cookies Objective: To be familiar with cookies Concepts. Topics what is a cookie? The Java Cookie class. Setting a cookie. handling cookies in JSP pages. Example Using Cookies. what is a cookie? Cookies are short pieces of data sent by web servers to the client browser. The cookies are saved to clients hard disk in the form of small text file. Cookies helps the web servers to identify web users, by this way server tracks the user. Cookies play very important role in the session tracking. The Java Cookie class The Servlet API includes a Cookie class to wrap up the contents of a cookie plus a few attributes. There are generally two stages to using a cookie: 1. first, we will want to ask the client set a cookie. 2. Then, we'll want to read the value of the cookie. Once we ask a client to set a cookie, then the client should send us back that cookie in any request to the domain/path that the cookie is defined for. 2

3 Setting a cookie To ask the client to set a cookie, we create a Cookie object and then add it to the HTTP response that our Servlet sends back: 3 public void doget(httpservletrequest req, HttpServletResponse res) throws ServletException, IOException { // read from the request the uesr's desired result per page Cookie ck = new Cookie("prefResultsPerPage", resperpage); res.addcookie(ck); // now write response as normal... The constructor takes the essential parameters of a cookie: name value There's no absolute limit to the length of either, but the cookie specification only recommends 4K as the minimum requirement for the length of a cookie, and it appears that some browsers have indeed imposed this rather meager limit. According to the specification, the 4K limit includes name, value plus the attributes (in the format sent in the HTTP header). handle cookies in JSP pages you will learn how to add cookies through jsp page and then show the value of the same cookie in another JSP page. Cookie Class In JSP cookie are the object of the class javax.servlet.http.cookie. This class is used to creates a cookie, a small amount of information sent by a servlet to a Web browser, saved by the browser, and later sent back to the server. A cookie's value can uniquely identify a client, so cookies are commonly used for session management. A cookie has a name, a single value, and optional attributes such as a comment, path and domain qualifiers, a maximum age, and a version number. The getcookies() method of the request object returns an array of Cookie objects. Cookies can be constructed using the following code: Cookie(java.lang.String name, java.lang.string value)

4 Cookie objects have the following methods: Method getcomment() getmaxage() getname() getpath() getvalue() setcomment(string) setmaxage(int) setpath(string) setvalue(string) Description Returns the comment describing the purpose of this cookie, or null if no such comment has been defined. Returns the maximum specified age of the cookie. Returns the name of the cookie. Returns the prefix of all URLs for which this cookie is targeted. Returns the value of the cookie. If a web browser presents this cookie to a user, the cookie's purpose will be described using this comment. Sets the maximum age of the cookie. The cookie will expire after that many seconds have passed. Negative values indicate the default behavior: the cookie is not stored persistently, and will be deleted when the user web browser exits. A zero value causes the cookie to be deleted This cookie should be presented only with requests beginning with this URL. Sets the value of the cookie. Values with various special characters (white space, brackets and parentheses, the equals sign, comma, double quote, slashes, question marks, the "at" sign, colon, and semicolon) should be avoided. Empty values may not behave the same way on all browsers. 4

5 Example Using Cookies No we will write code in JSP file to set and then display the cookie. Create Form Here is the code of the form (cookieform.jsp) which prompts the user to enter his/her page language="java" <html> <head> <title>cookie Input Form</title> </head> <body> <form method="post" action="setcookie.jsp"> <p><b>enter Your Name: </b><input type="text" name="username"><br> <input type="submit" value="submit"> </form> </body> Above form prompts the user to enter the user name. User input are posted to the setcookie.jsp file, which sets the cookie. Here is the code of setcookie.jsp page language="java" import="java.util.*" String username=request.getparameter("username"); if(username==null) username=""; Date now = new Date(); String timestamp = now.tostring(); Cookie cookie = new Cookie ("username",username); cookie.setmaxage(365 * 24 * 60 * 60); response.addcookie(cookie); <html> <head> <title>cookie Saved</title> </head> <body> <p><a href="showcookievalue.jsp">next Page to view the cookie value</a><p> </body> 5

6 Above code sets the cookie and then displays a link to view cookie page. Here is the code of display cookie page page language="java" String cookiename = "username"; Cookie cookies [] = request.getcookies (); Cookie mycookie = null; if (cookies!= null) { for (int i = 0; i < cookies.length; i++) { if (cookies [i].getname().equals (cookiename)) { mycookie = cookies[i]; break; <html> <head> <title>show Saved Cookie</title> </head> <body> if (mycookie == null) { No Cookie found with the name =cookiename else { <p>welcome: =mycookie.getvalue(). </body> When user navigates to the above the page, cookie value is displayed. 6

7 7 The output of the program is given below: