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Also, if the user exits and then restarts the browser and calls the servlet, the cookies that have not yet expired will continue to exist andwill be displayed when the server responds to the request. Thus, a session being tracked by cookies with a long maximum age can persist over long periods oftime, even when the computer has been shut down and restarted. (Many web sites will remember you on the same computer using the same browser over days,months, and even years.)
Beginning of the doGet method
Listing 1 shows the beginning of the controlling class and the beginning of the doGet method. You have seen code like this before, so I won't discuss it further in this module.
| Listing 1 - Beginning of the doGetmethod. |
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public class Java4570a extends HttpServlet{
public void doGet(HttpServletRequest request,HttpServletResponse response)
throws ServletException, IOException{ |
Construct a unique session ID
Listing 2 constructs a unique session ID that is later written into a cookie on the browser.
| Listing 2 - Construct a unique session ID. |
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String uid = new java.rmi.server.UID().toString();
String sessionID = java.net.URLEncoder.encode(uid); |
A UID object
The first step is to get a String representation of a UID object. According to the documentation, the UID class is an "Abstraction for creating identifiers that are unique with respect to the host on which it is generated."
Some cleanup is required
The second step is to call the encode method of the URLEncoder class to convert the string into a MIME format called the "x-www-form-urlencoded" format. This ensures that the identifier can be reliably transmitted between the server and the client andthat it will contain only those characters that are acceptable for saving in a cookie (see documentation on the setValue method of the Cookie class for more information) .
To convert the String , each character is examined and modified as follows:
A typical session identifier created by this process might appear as follows:
1cce64%3Ad69878ccf0%3A-7ff9
Get all of the cookies into an array of type Cookie
Listing 3 calls the getCookies method of the incoming HttpServletRequest object to get and save the cookies submitted by the browser. The values of the cookies will be displayed later.
| Listing 3 - Get all of the cookies into an array of type Cookie. |
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Cookie[] cookies = request.getCookies(); |
Get and save submitted value
As in the sample programs in earlier modules, Listing 4 gets and saves the field value submitted by the client.
| Listing 4 - Get and save submitted value. |
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String name = request.getParameter("firstName");
response.setContentType("text/html"); |
Listing 4 also establishes the type of output.
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