【正文】 ( 2 ) Cost reduction, it is more to select. All know windows in the puter of top of a table on nearly one Tong world, browser has bee standard disposition, but on server operating system, windows is in absolute dominance position not. Current tendency is the application management software that uses the configuration of B/S all , need to install only in Linux server on , and safety is high. The so server option of operating system is many, no matter choosing those operating system, can let the most of ones use windows in order to the puter of top of a table of operating system does not get influence, this for make most popular free Linux operating system develop fast, Linux except operating system is free besides, it is also free to link database, this kind of option is very pupular. Say, many persons on daily, Sina website s , so long as having installed browser for can , and what need not know the server of Sina website to use is that what operating system, and in fact the most of websites do not use windows operating system really, but the puter of user is most of as installing to be windows operating system. ( 3 ) Application server operation data load value paratively. Servlet 和 Jsp 技術(shù)概要 軟件工程 081 婁文 520813130116 7 Since B/S configures management, software installation in server end ( Server ) on, it is been all right that work administrator need to manage server only, the user interface major logic of general affairs in server ( Server ) end pass through WWW browser pletely realization, lose the logic of general affairs very much in front( Browser) realization, all customer ends has only browser, work administrator need to do hardware maintenance only. But application server operation data load is heavier, once occuring server collapse to wait for problem, consequence is unimaginable. Therefore a lot of units have database to stock server , are ready for any eventuality. 5． Inexpensive A number of free or very inexpensive Web servers are good for development use or deployment of low or mediumvolume Web sites. Thus, with servlets and JSP you can start with a free or inexpensive server and migrate to more expensive servers with highperformance capabilities or advanced administration utilities only after your project meets initial success. This is in contrast to many of the other CGI alternatives, which require a significant initial investment for the purchase of a proprietary package. Price and portability are somewhat connected. For example, Marty tries to keep track of the countries of readers that send him questions by . India was near the top of the list, probably 2 behind the . Marty also taught one of his JSP and servlet training courses (see in Manila, and there was great interest in servlet and JSP technology there. Now, why are India and the Philippines both so interested? We surmise that the answer is twofold. First, both countries have large pools of welleducated software developers. Second, both countries have (or had, at that time) highly unfavorable currency exchange rates against the . dollar. So, buying a specialpurpose Web server from a . pany consumed a large part of early project funds. But, with servlets and JSP, they could start with a free server: Apache Tomcat (either standalone, embedded in the regular Apache Web server, or embedded in Microsoft IIS). Once the project starts to bee successful, they could move to a server like Caucho Resin that had higher performance and easier administration but that is not free. But none of their servlets or JSP pages have to be rewritten. If their project bees even larger, they might want to move to a distributed (clustered) environment. No problem: they could move to Macromedia JRun Professional, which supports distributed applications (Web farms). Again, none of their servlets or JSP pages have to be rewritten. If the project bees quite large and plex, they might Servlet 和 Jsp 技術(shù)概要 軟件工程 081 婁文 520813130116 8 want to use Enterprise JavaBeans (EJB) to encapsulate their business logic. So, they might switch to BEA WebLogic or Oracle9i AS. Again, none of their servlets or JSP pages have to be rewritten. Finally, if their project bees even bigger, they might move it off of their Linux box and onto an IBM mainframe running IBM WebSphere. But once again, none of their servlets or JSP pages have to be rewritten. 6． Secure One of the main sources of vulnerabilities in traditional CGI stems from the fact that the programs are often executed by generalpurpose operating system shells. So, the CGI programmer must be careful to filter out characters such as backquotes and semicolons that are treated specially by the shell. Implementing this precaution is harder than one might think, and weaknesses stemming from this problem are constantly being uncovered in widely used CGI libraries. A second source of problems is the fact that some CGI programs are processed by languages that do not automatically check array or string bounds. For example, in C and C++ it is perfectly legal to allocate a 100element array and then write into the 999th element, which is really some random part of program memory. So, programmers who forget to perform this check open up their system to deliberate or accidental buffer overflow attacks.