【正文】 ted for each HTTP request. If the CGI program itself is relatively short, the overhead of starting the process can dominate the execution time. With servlets, the Java virtual machine stays running and handles each request with a lightweight Java thread, not a heavyweight operating system process. Similarly, in traditional CGI, if there are N requests to the same CGI program, the code for the CGI program is loaded into memory N times. With servlets, however, there would be N threads, but only 9 a single copy of the servlet class would be loaded. This approach reduces server memory requirements and saves time by instantiating fewer objects. Finally, when a CGI program finishes handling a request, the program terminates. This approach makes it difficult to cache putations, keep database connections open, and perform other optimizations that rely on persistent data. Servlets, however, remain in memory even after they plete a response, so it is straightforward to store arbitrarily plex data between client requests. 2． Convenient Servlets have an extensive infrastructure for automatically parsing and decoding HTML form data, reading and setting HTTP headers, handling cookies, tracking sessions, and many other such highlevel utilities. In CGI, you have to do much of this yourself. Besides, if you already know the Java programming language, why learn Perl too? You39。re already convinced that Java technology makes for more reliable and reusable code than does Visual Basic, VBScript, or C++. Why go back to those languages for serverside programming? 3． Powerful Servlets support several capabilities that are difficult or impossible to acplish with regular CGI. Servlets can talk directly to the Web server, whereas regular CGI programs cannot, at least not without using a serverspecific API. Communicating with the Web server makes it easier to translate relative URLs into concrete path names, for instance. Multiple servlets can also share data, making it easy to implement database connection pooling and similar resourcesharing optimizations. Servlets can also maintain information from request to request, simplifying techniques like session tracking and caching of previous putations. 4． Portable Servlets are written in the Java programming language and follow a standard API. Servlets are supported directly or by a plugin on virtually every major Web server. Consequently, servlets written for, say, Macromedia JRun can run virtually unchanged on Apache Tomcat, Microsoft Inter Information Server (with a separate plugin), IBM WebSphere, iPla Enterprise Server, Oracle9i AS, or StarNine WebStar. They are part of the Java 2 Platform, Enterprise Edition (J2EE。 see so industry support for servlets is being even more pervasive. 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 10 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.