Servlet life cycle

Three ways to use servlet

1. Implement Servlet interface
2. Extends GenericServlet
3. Extends HttpServlet

Servlet Functions:

void	destroy()           Called by the servlet container to indicate to a servlet that the servlet is being taken out of service.
ServletConfig	getServletConfig()           Returns a ServletConfig object, which contains initialization and startup parameters for this servlet.
java.lang.String	getServletInfo()           Returns information about the servlet, such as author, version, and copyright.
void	init(ServletConfig config)           Called by the servlet container to indicate to a servlet that the servlet is being placed into service.
void	service(ServletRequest req, ServletResponse res)           Called by the servlet container to allow the servlet to respond to a request.

init: only run one time when the very first request
destory: only run once when web server stop webapp
service: run once per request



HttpServlet Functions:

doGet
doPost


urlPatterns:

using wildcard '*' character
1: start with "/" ends with "/*"
2. "*.extension" (no "/" at beginning)

url mapping rules:
1. looking for more specific mapping first (only count from left to right)
2. "*.extension" have lower priority than others(based on 1's left to right rule)


HttpServletResponse

setContentType("text/html")
setCharacterEncoding("utf-8")
setCharacterEncoding()


Servlet Config xml
<servlet>
    <init-param>
        <param-name></param-name>
        <param-value></param-value>
    </init-param>
    <load-on-startup>1</load-on-startup> : servlet init() when load, value is call sequence
</servlet>

<context-param> </context-param> :

Or

@WebServlet(name="InitServlet", urlPatterns="/InitServlet", loadOnStartup=1)

To override init or destroy function, for site open/close actions,
remember to set that servlet loadOnStartup, in case that servlet never been called

ServletConfig object

this.getServletConfig().getInitParameter("encoding")
Enumeration<String> names = getServletConfig().getInitParameterNames();
while(names.hasMoreElements()){
    String name = names.nextElement();
    ...
}

Redirection

Sendredirect
request.getRequestDispatcher("/Login").forward(request, response);