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GenericServlet vs HttpServlet

 
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Hello everyone,

What are the differences between GenericServlet and HttpServlet?

Why we can't use session and cookies while GenericServlet is protocol independent (so it can handle any type of protocol)?

What GenericServlet can do and HttpServlet can't?

Thank you.



 
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HttpServlet IS A GenericServlet. GenericServlet doesn't expose cookies because not all protocols use cookies.
 
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As you have mentioned, GenericServlet is for protocol-independent servlets, and is a base class for protocol-specific servlet classes.

For servlets which deal with HTTP protocol, HttpServlet extends GenericServlet with HTTP-specific functionality.
Similarly for SIP protocol, SipServlet extends GenericServlet with SIP-specific functionality.
 
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Julio leopard banderas wrote:GenericServlet is protocol independent (so it can handle any type of protocol)


It's quite the opposite: GenericServlet handles no type of protocol. That is for the extending classes to provide.
 
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J2EE doesn't actually assume that the only way to do servlets is via an HTTP server. The GenericServlet is the base class for any sort of server that works in a request/response paradigm. For example, long before Java was invented, IBM had a lightweight interactive application system called CICS. Actually, still, has, but back before PCs, TCP/IP, HTTP and the entire Internet, you needed something like that or be stuck juggling tapes and punched cards.

So GenericServlet could be used as a base class for a CICS application. And for all I know, it has been, although I got out of the mainframe-only world before Java came along, so I'm no longer in touch with IBM-specific products.

For webapps, you'l almost always want to use HttpServlet, since it affords the extra amenities that HTTP has to offer.

Note that this isn't the only case where Sun has distanced itself from specific frameworks. JavaServer Faces was also designed with the idea that HTML would not be the only possible form framework. And in fact, back then, WAP was used on many phones. Only when smartphones became the norm did WAP get pushed aside by HTML/CSS/JavaScript.
 
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Also see https://coderanch.com/wiki/659865/Servlets-Faq#otherProtocols
 
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The main difference is that, HttpServlet is a protocol dependent whereas GenericServlet is protocol independent. So GenericServlet can handle all types of protocols, but HttpServlet handle only HTTP specific protocols.
 
Stephan van Hulst
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Wrong. As Bear has said, GenericServlet handles NO protocol.
 
Tim Moores
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I think that's a question of semantics: GenericServlet handles no protocol specifically, but it handles all protocols because all protocol-dependent classes that extend it inherit its (admittedly rudimentary) code - which is thus used to handle all those protocols.

So I would say GenericServlet implements no protocol, but it handles all of them.
 
Tim Holloway
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I'm going to split the difference. GenericServlet handles no protocols. That's done elsewhere, out of sight. It could be said to support all request/response protocols, and that includes those that are entirely internal to the application, with no networking whatsoever.

That is, if I wanted to build an application framework where the applications were processing modules that were fed input from a single source and produced output to a single response point, I could make those applications "pluggable" by basing them on GenericServlet.
 
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