【正文】 servlets. The Advantages of Servlets Over Traditional CGI Java servlets are more efficient, easier to use, more powerful, more portable, safer, and cheaper than traditional CGI and many alternative CGIlike technologies. 1． Efficient With traditional CGI, a new process is started 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 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。t know how to use them, what good are they? Servlet and JSP technology is supported by servers from Apache, Oracle, IBM, Sybase, BEA, Macromedia, Caucho, Sun/iPla, New Atlanta, ATG, Fujitsu, Lutris, Silverstream, the World Wide Web Consortium (W3C), and many others. Several lowcost plugins add support to Microsoft IIS and Zeus as well. They run on Windows, Unix/Linux, MacOS, VMS, and IBM mainframe operating systems. They are the single most popular application of the Java programming language. They are arguably the most popular choice for developing medium to large Web applications. They are used by the airline industry (most United Airlines and Delta Airlines Web sites), emerce (), online banking (First USA Bank, Banco Popular de Puerto Rico), Web search engines/portals (), large financial sites (American Century Investments), and hundreds of other sites that you visit every day. Of course, popularity alone is no proof of good technology. Numerous counterexamples abound. But our point is that you are not experimenting with a new and unproven technology when you work with serverside Java. Servlet 和 JSP 技術簡述 Nagle and Wiegley， Aug. 2020， 953 – 958. 摘要： Servlet 程序在服務器端運行，動態(tài)地生成 Web 頁面與傳統的 CGI 和許多其他類似 CGI 的技術相比， Java Servlet 具有更高的效率，更容易使用，功能更強大，具有更好的可移植性，更節(jié)省投 資。 最終用戶一般在頁面的 HTML 表單中輸入這些數據。兩種數據都很重要。實際的數據可能存儲在關系型數據庫中。因此，我們需要 Web 中間層從 HTTP流中提取輸入數據，與應用程序會話，并將結果嵌入到文檔中。 （ 5） 發(fā)送隱式的 HTTP 響應數據。 HTTP 響應數據的發(fā)送過程涉及告知瀏覽器或其他客戶程序所返回文檔的類型（如 HTML），設置 cookie 和緩存參數，以及其他類似的任務。 例如，搜索引擎生成的頁面，以及在線商店的訂單確認頁面，都要針對特定的用戶請求而產生?；?cookie 值針對具體用戶構建頁面的情況尤其普遍。具體應該采用哪種方式要根據具體情況而定，但后一種方式常常更為方便，因為它只需簡單地等待用戶的請求。想象以下，如果一個搜索引擎網站完全使用 applet，那么用戶將會看到： “正在下載 50TB 的 applet，請等待！ ”。 理論上講， servelt 并非只用于處理 HTTP 請求的 Web 服務器或應用服務器，它同樣可以用于其他類型的服務器。 效率 應用傳統的 CGI，針對每個 HTTP 請求都用啟動一個新的進程。同樣的情況，如果使用 servlet 則啟動 N 個線程，單僅僅載入 servlet 類的單一副本。然而， servelt 會一直停留在內存中（即使請求處理完畢），因而可以直接存儲客戶請求之間的任意復雜數據。 Servlet 能夠直接于Web 服務器對話，而常規(guī)的 CGI 程序做不到這一點，至少在不使用服務器專有 API的情況下是這樣。 可移植性 Servelt 使用 Java 編程語言，并且遵循標準的 API。為 Macromedia JRun編寫的 servlet，可以不經過任何修改地在 Apache Tomcat， Microsoft Inter Information Server， IBM WebSphere 。 廉價