Java Reference
In-Depth Information
If the fi rst version is used or the second version is used with an argument of
true
, then the server returns the current session if there is one; otherwise, it creates
a new session object. For example:
HttpSession cart = request.getSession();
If the second version is used with an argument of
false
, then the current session
is returned if there is one, but
null
is returned otherwise.
A session object contains a set of name-value pairs. Each name is of type
String
and each value is of type
Object
. Note that
objects added to a session must imple-
ment the
Serializable
interface
. (This is true for the
String
class and for the type
wrapper classes such as
Integer
.) A servlet may add information to a session object
via the following method:
void setAttribute(String <name>, Object <value>)
Example
String currentProduct = request.getParameter("Product");
HttpSession cart = request.getSession();
cart.setAttribute("currentProd",currentProduct);
The method to remove an item is
removeAttribute
, which has the following signature:
Object removeAttribute(String <name>)
For example:
cart.removeAttribute(currentProduct);
To retrieve a value, use:
Object getAttribute(String <name>)
Note that a
typecast
will usually be necessary after retrieval. For example:
String product =
(String)cart.getAttribute("currentProd");
To get a list of all named values held, use:
String[] getAttributeNames()
For example:
String[] prodName = cart.getAttributeNames();
It's now time to put these individual pieces together into a full example
application…
Example
This example involves a simplifi ed shopping cart into which the user may place a
specifi ed weight of apples and/or a specifi ed weight of pears. Three servlets are
used, for the following purposes:
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