servlet development

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servlet

Development initial

Servlet is an application technology in the Java language in the web server, and future servlets will thoroughly replace CGI. This lecture will specifically introduce the concept, development, commissioning, and corresponding application examples of servlets.

First, what is servlet?

· Servlet is a Java application that is independent of the platform and protocol, which can generate a dynamic web page.

· Servlet is a Java application located within the server side within the web server. Unlike the traditional Java application launched from the command line, the servlet is loaded by the web server, which must contain Java virtual machines that support servlet.

• The relationship between servlet and web server is similar to the relationship between Applet and web browsers (this is why servlet technology is called servlet), we can imagine servlets to do not have an APPLET without front-end interface (Faceless). Unlike Applets, because servlet runs in the web server side, it is a trusted program that is not limited by Java security, with the same permissions as ordinary Java applications.

· Servlet is an alternative technology for CGI Script, because servlet has a significant advantage over the performance, portability, code reuse, etc., so servlets may completely replace CGI during future technology development.

Second, write the development environment required by servlet

The basic environment required for servlet development is JSDK and a web server that supports servlet.

1.JSDK (Java Servlet Development Kit)

JSDK contains the Java class libraries that compile the servlet application and related documents. For users developed using Java 1.1, JSDK must be installed. JSDK has been integrated into the Java 1.2 Beta, so if you develop using Java 1.2, you don't have to install JSDK.

JSDK can download free download of JavaSoft's site, its address is

http://jserv.javasoft.com/products/java-server/downloads/index.html

2. Support the WEB server for servlet

Servlet needs to run on a web server that supports servlet. Currently supporting the WEB server of Servlet to push Sun's Java Web Server. If the existing web server does not support servlet, you can use some third-party manufacturers' server add-up (add-ons) to enable the web server to support servlet, where Live Software (http://www.livesoftware) is available. A product called JRUN allows Microsoft IIS and Netscape Web Server to support servlet by installing the corresponding version of JRUN.

Third, the process of developing a servlet

This article will describe the process of developing a servlet with a simple servlet (we call HelloServlet).

Write a servlet code

The Java Servlet API is a standard Java extension package that contains two packages :javax.servlets and javax.servlet.http. For developers who want to develop customer-defined protocols, you should use the class and interface in the Javax.Servlet package; for developers with the HTTP protocol to interact with the client, just need to use javax.servlet.http package The class can be developed with the interface.

Below is a typical servlet program code:

Import javax.servlet. *;

Import javax.servlet.http. *;

Import java.io. *; import java.util. *;

Public class helloservlet extends httpservlet {

Public void init (servletconfig config) throws servletexception {

Super.init (config);

}

Public Void Service (httpservletRequest Req, httpservletResponse res)

Throws servletexception, ioException {

String clientipaddress = req.getRemoteAddr ();

Res.SetContentType ("text / html");

ServletOutputStream out = res. maxOutputStream ();

Out.println ("");

Out.println ("