【正文】 以分配一個 100 個元素的數(shù)組，然后向第 999 個 “ 元素 “ 寫入數(shù)據(jù) —— 實際上是程序內存的隨機部分，這完全合法。當然，數(shù)組邊界的檢查以及其他內存包含特性是 java 編程語言的核心部分。 當然，僅僅是流行并不能證明技術的優(yōu)越性。s Job Servlets are Java programs that run on Web or application servers, acting as a middle layer between requests ing from Web browsers or other HTTP clients and databases or applications on the HTTP server. Their job is to perform the following tasks, as illustrated in Figure 11. Figure 11 1． Read the explicit data sent by the client. The end user normally enters this data in an HTML form on a Web page. However, the data could also e from an applet or a custom HTTP client program. 2． Read the implicit HTTP request data sent by the browser. Figure 11 shows a single arrow going from the client to the Web server (the layer where servlets and JSP execute), but there are really two varieties of data: the explicit data that the end user enters in a form and the behindthescenes HTTP information. Both varieties are critical. The HTTP information includes cookies, information about media types and pression schemes the browser understands, and so on. 3． Generate the results. This process may require talking to a database, executing an RMI or EJB call, invoking a Web service, or puting the response directly. Your real data may be in a relational database. Fine. But your database probably doesn39。 you need to talk to the database. Going from the client to the Web tier to the database (a threetier approach) instead of from an applet directly to a database (a twotier approach) provides increased flexibility and security with little or no performance penalty. After all, the database call is usually the ratelimiting step, so going through the Web server does not slow things down. In fact, a threetier approach is often faster because the middle tier can perform caching and connection pooling. In principle, servlets are not restricted to Web or application servers that handle HTTP requests but can be used for other types of servers as well. For example, servlets could be embedded in FTP or mail servers to extend their functionality. And, a servlet API for SIP (Session Initiation Protocol) servers was recently standardized (see In practice, however, this use of servlets has not caught on, and we39。t support them and developers don39。re already convinced that Java technology 11 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。t talk directly to the database. Even if it could, for security reasons, you probably would not want it to. The same argument applies to most other need the Web middle layer to extract the results inside a document. 4． Send the explicit data (., the document) to the client