由servlet设置的属性存储在哪里? [英] Where are the attributes stored, which are set by servlets?
问题描述
下面是我的servlet:
Below is my servlet:
public class ServletExample extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
if(request.getParameter("firstname") == null || request.getParameter("lastname") == null){
this.getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
return;
}
String firstName = request.getParameter("firstname");
String lastName = request.getParameter("lastname");
request.setAttribute("firstname", firstName);
request.setAttribute("lastname", lastName);
this.getServletContext().getRequestDispatcher("/output.jsp").forward(request, response);
}
}
以下是我的index.jsp:
<?xml version="1.0" encoding="ISO-8859-1" ?>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
<title>Insert title here</title>
</head>
<body>
<form action="servletexample" method="post" >
<table border="0">
<tr>
<td>First Name:</td> <td><input type="text" name="firstname" /></td>
</tr>
<tr>
<td>Last Name:</td> <td><input type="text" name="lastname" /></td>
</tr>
<tr>
<td colspan="2"> <input type="submit" value="Submit" /></td>
</tr>
</table>
</form>
</body>
</html>
以下是我的output.jsp:
<?xml version="1.0" encoding="ISO-8859-1" ?>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
<title>Insert title here</title>
</head>
<body>
<h1>Your first and last name is: </h1>
<%
/*String firstName = (String)request.getAttribute("firstname");
String lastName = (String)request.getAttribute("lastname");*/
String firstName = request.getParameter("firstname");
String lastName = request.getParameter("lastname");
out.print(firstName + " " + lastName);
%>
</body>
</html>
我了解到，当加载Web应用程序时，servlet容器将创建一次ServletContext并将其保留在服务器的内存中. ServletContext是适用于整个Web应用程序的属性和配置的集合
I learnt that, When a webapplication gets loaded, the servletcontainer will create the ServletContext once and keep in server's memory. ServletContext is a collection of attributes and configurations that apply to the entirety of your web application
按照上述servlet示例，request.setattribute用于创建新属性.
As per above servletexample, request.setattribute is used to create a new attribute.
1)
这些属性是否存储在ServletContext中?
Are these attributes stored in ServletContext?
2)
ServletContext中存储的那些属性和配置是什么?
What are those attributes and configurations that is stored in ServletContext?
推荐答案
有三个范围:
- 应用范围(即SevletContext)
- 会话范围(即HttpSession)
- 请求范围(即HttpServletRequest)
获取ServletContext对象:
Getting ServletContext Object:
-
getServletContext().set attribute("name"，"value"); //现在的名字 属性可以从应用程序内的任何Servlet进行访问.
getServletContext().set attribute("name","value"); //now the name attribute will be accessible from any Servlet within the application.
获取HttpSession对象:
Getting HttpSession Object:
request.getSession(true).set attribute("name2"，"value"); //现在可以从当前会话访问name2属性
request.getSession(true).set attribute("name2","value"); //now the name2 attribute will be accessible from current session
request.set attribute("name3"，"value");
request.set attribute("name3","value");
//现在，在将响应发送回客户端之前，可以在Servlet或jsp中的任何位置访问name3属性.
//now the name3 attribute will be accessible anywhere in Servlet or jsp before sending response back to the client.
是:属性存储在哪里?
回答:属性存储在相应范围的Map(名称/值对)中. 即会话映射，请求映射和ServletContext映射.
Ans: Attributes are stored in a Map(in name-value pair) of respective Scope. i.e. Session Map, Request Map and ServletContext Map.
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