发信人: crazyjava()
整理人: (1999-11-10 08:57:37), 站内信件
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【 以下文字转载自 SystemAnalysis 讨论区 】
【 原文由 骄傲的中国人 所发表 】
CGI
A second, very popular way of communicating over a computer
network(possibly the most popular way), is via CGI. CGI is
a way to program your Web server so that it can offer more
than the static form of HTML documents. When a client requests
a CGI page, the server runs a program (identified by a special
from of URL) that builds an HTML page on the fly. The server
then transmits page can perform a simple computation, access
a database, access another host, or do almost anything
necessary to acquire the data it includes in the requested
page.
The handy thing about CGI is that it is supported by every Web
browser and essentially every Web server.
Despite its ease of use and popularity, however, CGI has some
serious drawbacks:
1) CGI is slow. Tests reported by Orfali and Harkey(my teachers),
leading authorities on client-server computing, show that CGI
is about 200 times slower than IIOP.
2) CGI can compromise server security. CGI is a jerrybuilt
extension to Web servers. Many sites have been compromised
by hackers who have exploited weaknesses arising from the
inadequate integration between a Web server and the CGI
programs it spawns.
3) CGI cannot store state information. HTTP is a stateless
protocol. This means that Web browsers (and other HTTP
clients) are connected to Web servers only for the duration
of a single request. A browser cannot ask the server to
remember who it is, or anything about its previous requests.
The client must store this information and re-transmit it
with any request that needs it.
The Servlet Alternative
The limitation of CGI architecture led Sun to introduce its
own alternative based on Java, the JavaServer architecture.
JavaServer introduces the servlet, which is a java program
that in many ways resembles an applet, but that runs on the
server rather than on the client. Clients can request that
servlets be started and can obtain results produced by
servlets. Like client-side applets, servlets run under control
of a security manager that monitors their artivities, preventing
them from performing actions that might threaten system security.
Moreover, servlets, though they are written in Java, run more
effeiciently than CGI scripts.
Because servlets are written in Java, they can invoke any of
Java's APIs or facilites. Thus, for example, a servlet could
use RMI to comminicate with a second rmote server, or with the
originally requesting client. This chameleon characteristic
makes it difficult to anticipate the typical ways in which
servlets may someday come to be used, if they gain a permanent
foothold in the computing marketplace.
When might you choose to use CGI as a means of communicating
with a remote server? If performance is not a major concern
and you're concern with providing access to a wide variety of
clients (for example, the public), then CGI has important
strenghts. If, on the other hand, your are creating applications
that will be confined to your own organization, some other
approach will probably serve you better. Servlets are an
interesting alternative because they provide the same strength
as CGI with fewer drawbacks.
/Crazyjava
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※ 修改:．crazyjava 于 Jul 30 17:04:06 修改本文．[FROM: 139.87.93.173]
※ 来源:．月光软件站 http://www.moon-soft.com．[FROM: 139.87.93.173]
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※ 转载:．月光软件站 http://www.moon-soft.com．[FROM: 139.87.93.173]
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