Two fatal disadvantages of Servlet (interview questions):
- There are many configuration items in web.xml file: due to the increase of Servlet, a large number of Servlet configurations will be generated
- Servlet has container dependency reason: HttpServletRequest and HttpServletResponse objects are created by the Web container when a servlet processes a get or post request
Implementation steps of ActionServlet:
1. Create Action interface:
public interface Action {
public String execute(HttpServletRequest request,HttpServletResponse response);
}
2. Create an Action to override the Action interface:
public class HelloWorld implements Action{
@Override
public String execute(HttpServletRequest request, HttpServletResponse response) {
System.out.println("action Access succeeded!"); //Prompt the processing method of Action to be executed
return "index.jsp"; //Return the Action address to be redirected
}
}
3. Create ActionFilter (a method to implement Filter interface rewriting Filter life cycle):
public class ActionFilter implements Filter{
private HttpServletRequest request = null; //Create an http request object. Private httpservletresponse = null; / / create an http response object
@Override
public void init(FilterConfig filterConfig) throws ServletException {
// TODO Auto-generated method stub
}
@Override
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
//Get HTTP request and response objects
this.request = (HttpServletRequest)request;
this.response = (HttpServletResponse)response;
/*
Get the uri of the action to be accessed through HttpServletRequest
ServletRequest must be converted to HttpServletRequest to get URI
*/
String uri = this.request.getRequestURI();
String actionName = ActionUtil.getActionName(uri);//Get the name of the Action by parsing the uri string with getActionName()
try {
Action action = (Action)Class.forName("th.action."+actionName).newInstance(); //Create Action object through reflection mechanism
String page = action.execute(this.request, this.response); //Discard the Action processing method and return the request and response back
this.request.getRequestDispatcher(page).forward(this.request, this.response); //Redirect according to the jump page string returned by Action
} catch (InstantiationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
@Override
public void destroy() {
// TODO Auto-generated method stub
}
}
getAction() method to resolve URI:
public class ActionUtil {
public static String getActionName(String uri){
String[] str = uri.split("/");
String result = str[str.length-1].substring(0, str[str.length-1].indexOf("."));
return result;
}
}
4. To configure the Filter filter in Web.xml:
<filter>
<filter-name>ActionFilter</filter-name>
<filter-class>th.filter.ActionFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>ActionFilter</filter-name>
< URL pattern > *. Action < / url pattern > <! -- distinguish whether to access action or servlet according to the address with suffix ending with *. Action -- >
</filter-mapping>
5. Create a test jsp page:
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title></title>
</head>
<body>
<a href="HelloWorld.action" >Request one action</a> //To distinguish whether a servlet or an action is accessed, use the href="*.action"
</body>
</html>