Javaweb Learn what a servlet is, how to use a servlet, why this is used, the virtual path of the servlet (2)

 1. What is a servlet?    * Server-side Java programs, Servlets need to be handed to the server to run. * Java program related to Javax.servlet.Servlet interface 2, how to use servlet? "Must" * Create a WEB project * Create a class and implement a servlet interface * to the server to run/web-inf/web.xml<!--Register Servlets <servlet> Tags: servlet registration <servlet-class> Tags: determining where a servlet class is located                        * Content: The full pathname <servlet-name> tag of the servlet class that needs to be registered: an alias for the servlet, provided for use by other programs * Content: Custom * required, must be unique -        <servlet>            <Servlet-name>HelloWorld</Servlet-name>            <Servlet-class>Com.yxl.HelloWorld</Servlet-class>        </servlet>        <!--servlet Mappings <servlet-mapping> Tags: mapping an existing servlet <servlet-name> tag: determining the Used The name of the servlet * content: From the previously configured <servlet><servlet-name> content <url-pattern> Tags: ok Browser Access Path * Content: Custom * Requirements: Must start with "/", name unique -        <servlet-mapping>            <Servlet-name>HelloWorld</Servlet-name>            <Url-pattern>/hello</Url-pattern>        </servlet-mapping>* Test: Http://localhost:8080/day05/hello 3, why use this?            * Javax.servlet.Servlet life cycle: * init (servletconfig servletconfig) * Servlet initialization method, number of executions: 1 times * Javax.servlet.ServletConfig Description of configuration information for current servlet * SERVLETCONFIG.GETSERVLETNAME (): Returns the name of the current servlet: <servlet><Servlet-name>contents of configuration * Servletconfig.getinitparameter ("paramname"): Returns the value of the specified initialization parameter name, reading the configuration file Web. XML * <servlet>                            <Servlet-name>helloWorld222</Servlet-name>                            <Servlet-class>Cn.itcast.HelloWorld2</Servlet-class>                            <!--Configuring the initialization parameter list -                            <Init-param>                                <!--the name of the initialization parameter -                                <Param-name>Gf</Param-name>                                <!--Initialize the value of the parameter -                                <Param-value>Fengjie</Param-value>                            </Init-param>                        </servlet>                * Servletconfig.getinitparameternames (): Returns the name of all initialization parameters of the current servlet * return value: Java.util.Enumera tion-hasmoreelements (), nextelement () *servletcontext ServletContext = Servletconfig.getservletconte XT (): ServletConfig save ServletContext Reference to current Web project [suspense] *service (servletrequest,servletresponse) "* *" * Current Ser  Vlet method called on request and Response * ServletRequest: Store all user's request information * Servletresponse: Store all information that the server responds to the user * Summary * Request * Interface: Javax.servlet.ServletRequest * Implementation class: Org.apache.cata Lina.connector.RequestFacade * Relationship: * Public class Requestfacade implements HttpS  Ervletrequest {* Public interface HttpServletRequest extends ServletRequest {* Summary: Requestfacade--HttpServletRequest--ServletRequest * Results: Javax.servlet.http.HttpServlet Request Request = (HttpSErvletrequest) req; * Response * Interface: Javax.servlet.ServletResponse * Implementation class: Org.apache.catalina.connector.Re Sponsefacade * Relationship: * Public class Responsefacade implements HttpServletResponse {* Public interface HttpServletResponse extends Servletresponse {* Summary: respons Efacade--HttpServletResponse-Servletresponse * Results: Javax.servlet.http.HttpServletResponse        Response = (httpservletresponse) resp;         * Destroy () * Current servlet destruction method, Recycle resource * Javax.servlet.GenericServlet class "See" This,super * generic Servlet implementation class, Protocol Independent * This class is abstract class, with abstract method service (servletrequest,servletresponse) * Public abstract Void Service (ServletRequest re        Q, Servletresponse Res) throws Servletexception, IOException; * This class implements the Servlet interface, which also implements the ServletConfig interface * Public abstract class Genericservlet implements Servlet, ServletconFig * This class caches the values of the actual parameters of the Init method. (ServletConfig instance object is cached) * public void init (ServletConfig config) throws servletexception {This                . config = config;              This.init ();            } * This class is recommended to overwrite this method in the absence of a parametric Init method that all servlet initialization works.            * Otherwise, overriding the Init method with parameters requires adding Super.init (config) to the first line of the method;                * public void init (ServletConfig config) throws servletexception {super.init (config);//This line code must exist            Then it's your own content} * Javax.servlet.http.HttpServlet class * This class is an abstract class, but there is no abstract method.            * Abstract class for reasons that require subclasses to make HttpServlet class method overrides * There is no reason for abstract methods: when subclasses override the corresponding way of the parent class, there is no mandatory requirement * This class is an implementation class for a servlet related to Protocol (HTTP)              * Request = (httpservletrequest) req;        Response = (httpservletresponse) res; * Request.getmethod () method, which returns the request method of the current servlet, facilitates and handles different requests * Summary: "* *" * Create a class that inherits the HttpServlet class * Based on requirements, Cover Dopost and Doget method * need to be configured in Web. * Test * NOTE: * If initialization work is required: overwriteInit () method * If the initialization work takes a lot of time, you need to set the servlet to initialize when the server starts.  *<servlet><Load-on-startup>2</Load-on-startup>* Configure current servlet load order at server startup, value: 0-6, lower value, priority load 4, servlet virtual path refers to<servlet-mapping>            <Servlet-name>HelloWorld</Servlet-name>            <Url-pattern>/hello</Url-pattern>        </servlet-mapping>in<Url-pattern>Path 1, only use/or * start 2,/and *. Cannot exist at the same time 3,/or/* indicates any 4, only *. To indicate a wildcard character

Javaweb Learn what a servlet is, how to use a servlet, why this is used, the virtual path of the servlet (2)