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<form name="UserInformation"> <input type="hidden" name="name" value="Stephan Wiesner" /> </form> generate, create none none with none projectspdf-417 generator .net Such fields none for none do not appear in the browser display, but will be sent with the rest of the form data that the user has entered when he or she submits the form. Hidden form fields are far from ideal however: they result in extra data traffic and the user can see them anyway by choosing View Source in their browser. They are one way that malicious users can attempt to mount an attack on your web application.

It is also possible for an unauthorized third party to view the data they contain by intercepting a user"s requests. This last problem can be eliminated with the use of SSL. Cookies are another simple way of identifying users.

They are very short text files stored on the user"s computer. While they are safe to use in updated browsers, their reputation is far from unblemished, and for that reason you can"t rely on all your users having them switched on. Give it a Thought! For a particular project, an entire web interface based on cookies was created.

Then a couple of e-mails were received from users complaining that the site didn"t work for them. The entire site was converted, which took several weeks, reasoning that for each user who complained, hundreds probably never bothered, and simply never came back..

GS1 DataBar bar codes Introduction to Struts The most el none none egant method is the use of a single session. Session is a Java object, much like Map, for storing other objects with a given name (or key). Each user is linked to their session either via a cookie or via URL-rewriting.

You should always use the latter, because subsequent changes are cumbersome to perform. However, if your application will be deployed on a private intranet where the environment can be "dictated", using cookies might be acceptable. The servlet specification advises to store only serializable objects in session.

You can, however, store other objects, but such objects will not be able to be restored in the event of a system failure. Servers such as WebSphere Application Server claim to be able to manage failures without losing such data, although you must be able to buffer the data. Another point to remember is that many servers can release session objects from storage as soon as they are buffered, allowing them to handle more users.

Session length Avoid overusing session; remember that every user will have his or her session on the server. There are projects where the developer allowed the session to grow to 40 MB. Naturally, as more and more users tried to access pages simultaneously, the demand on server memory increased very fast and quickly became unmanageable.

Normally a session should be no more than one or two KB, but the maximum size depends on how many visitors you expect. The following JSP code demonstrates how to store and retrieve items from session. It starts by storing a string value with setAttribute(), and a HashMap containing three further string values.

The code then iterates through an enumeration displaying every session item in the browser, as well as writing it out to a file. Finally it displays the size of the session. Listing 1.

1: SessionStorage.jsp. <%@page import="java.io.*, java.

util.*, javax.servlet.

http.*"%> <html> <body> <pre> <% out.println("Starting.

.."); session.

setAttribute("username", "Stephan"); HashMap map = new HashMap(); map.put("one", "First"); map.put("two", "Second"); map.

put("three", "Third"); session.setAttribute("map", map); ObjectOutput output = null; try { OutputStream file = new FileOutputStream( "test.ser" );.

1 . OutputStrea m buffer = new BufferedOutputStream( file ); output = new ObjectOutputStream( buffer ); Enumeration e = session.getAttributeNames(); while (e.hasMoreElements()) { String name = (String)e.

nextElement(); Object o = session.getAttribute(name); out.println(name + "=" + o); output.

writeObject(o); } output.close(); File f = new File("test.ser"); out.

println("Size:" + f.length()); } catch(IOException ex) { out.println("Error:" + ex); } %> </pre> </body> </html>.

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