【正文】 s 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 a nd 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 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. Servlets suffer from neither of these problems. Even if a servlet executes a system call (., with or JNI) to invoke a program on the local operating system, it does not use a shell to do so. And, of course, array bounds checking and other memory protection features are a central part of the Java programming language. 7． Mainstream There are a lot of good technologies out there. But if vendors don39。 2. 讀取由瀏覽器發(fā)送的隱式請求數(shù)據(jù)。即使它能夠做到這一 點(diǎn)，為了安全上的考慮，我們也不希望讓它這么做。但是，實(shí)際發(fā)送的數(shù)據(jù)有兩種：文檔本身，以及后臺的 HTTP信息。要記住，用戶提交兩種類型的數(shù)據(jù)：顯示（即 HTML 表單的數(shù)據(jù)）和隱式（即 HTTP請求的報(bào)頭）。 頁面中使用了來自公司數(shù)據(jù)庫或其他數(shù)據(jù)庫斷數(shù)據(jù)源的信息。而且，用于會話啟動協(xié)議服務(wù)器的 servlet API最近已經(jīng)被標(biāo)準(zhǔn)化（參見 servlet的這種用法尚不流行，在此，我們只論述 HTTP Servlet。最后，當(dāng) CGI 程序結(jié)束對請求的處理之后，程序結(jié)束。多個 servlet 還可以共享數(shù)據(jù)，從而易于實(shí)現(xiàn)數(shù)據(jù)庫連接共享和類似的資源共享