Java servlet

A Java servlet is a Java program that extends the capabilities of a server. Although servlets can respond to any types of requests, they most commonly implement applications hosted on Web servers. A Java servlet processes or stores a Java class in Java EE that conforms to the Java Servlet API, a standard for implementing Java classes that respond to requests.

A servlet is a Java programming language class that is used to extend the capabilities of servers that host applications accessed by means of a request-response programming model. Although servlets can respond to any type of request, they are commonly used to extend the applications hosted by web servers.

Servlets could in principle communicate over any client–server protocol, but they are most often used with the HTTP protocol. Thus "servlet" is often used as shorthand for "HTTP servlet". Thus, a software developer may use a servlet to add dynamic content to a web server using the Java platform. The generated content is commonly HTML, but may be other data such as XML. Servlets can maintain state in session variables across many server transactions by using HTTP cookies, or URL rewriting.

Compared with other web application models

The advantages of using servlets are their fast performance and ease of use combined with more power over traditional CGI. Traditional CGI scripts written in Java have a number of performance disadvantages:

● When an HTTP request is made, a new process is created each time the CGI script is called. The overhead associated with process creation can dominate the workload especially when the script does relatively fast operations. Thus, process creation will take more time for CGI script execution. In contrast, for servlets, each request is handled by a separate Java thread within the web server process, thereby avoiding the overhead associated with forking processes within the HTTP daemon. ● Simultaneous CGI requests will load the CGI script to be copied into memory once per request. With servlets, there is only one copy that persists across requests and is shared between threads. Only a single instance answers all requests concurrently. This reduces memory usage and eases the management of persistent data.
● A servlet can be run by a servlet container in a restrictive environment, called a sandbox. This is similar to an applet that runs in the sandbox of the web browser. This enables restricted use of potentially harmful servlets.CGI programs can of course also sandbox themselves, since they are simply OS processes.

Technologies like FastCGI and its derivatives do not exhibit the performance disadvantages of CGI, incurred by the constant process spawning. They are, however, roughly as simple as CGI.

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