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JSP implicit object -- scope

2022-07-26 07:58:00 【Super Qi】

jsp Implicit objects - Scope

session object ：

1. Definition ：

​ a. session Object is a session between client and server （ Connect to the server and start , Until the client is disconnected from the server ）

​ b. javax.serlvet.http.HttpSession Interface instance of

2. effect ：

​ session Object is used to save the information of each customer , Used to detect the usage status of each user （ Operation state ）

3. perform ：

​ session Object will give the new user a unique identifier session id And save it in the client's cookie in , Used to distinguish other customers

​ *session The information is stored in the client container ,session id Saved in the client's cookie in

4. Valid time ：（session Validity period of space ）

​ a. The user closes the browser program he is browsing

​ b. Shut down the web server

​ c. The user did not make a request to the server for more than the preset time ,Tomcat The server defaults to 30 minute

​ d. End of run session The program

5. session The common method of

​ getAttribute（String name）： Gets the property associated with the specified name .

​ getAttributeNames()： return session The object of every attribute stored in the object

​ getCreateTime()： Back to create session Time of object , The unit is millisecond

​ getId()： return session The object is on the server side id Number

​ getLastAccessedTime()： return session The request time when the object last sent the request

​ getMaxInactiveInterval()： return session The lifetime of the object , The unit is in seconds

​ setMaxInactiveInterval( int interval)： Set up session The lifetime of the object , The unit is in seconds

​ setAttribute(String name, java.lang.Object value)： Set the attribute value of the specified name attribute , And store it in session In the object

​ invalidate()： The destruction session object , Make the objects bound to it invalid

6. visit session Data in

a. establish session Variable ：

session.setAttribute(" Variable name ", Variable content （String type ）);

b. return session Data in （ obtain session The data in ）：

session.getAttribute(" Variable name "); // The type of return is Object type

c. eliminate session The variables in the ：

session.removeAttribute(" Variable name "); // Eliminate the named session Object's data

d. end session：

session.invalidate();   // take session end , The destruction session object

7.session Object instances ：

a. establish session Object and get session Object's data 

/***Demo1.jsp***/
<%@ page contentType="text/html;charset=UTF-8" language="java" pageEncoding="UTF-8" %>
<html>
<head>
    <title>session</title>
</head>
<body>
<%
    session.setAttribute("information"," towards session Save data in ");
    response.sendRedirect("Demo1_to.jsp");
%>
</body>
</html>

/***Demo1_to.jsp***/
<%@ page contentType="text/html;charset=UTF-8" language="java" pageEncoding="UTF-8" %>
<html>
<head>
    <title>session Save the information page </title>
</head>
<body>
<%
    out.print(session.getAttribute("information"));
%>
</body>
</html>

b. Set up session Object lifetime and cleanup assignments session Data of object name

​

/***Demo1_to.jsp***/
<%@ page contentType="text/html;charset=UTF-8" language="java" pageEncoding="UTF-8" %>
<html>
<head>
    <title>session Save the information page </title>
</head>
<body>
<%
    out.print(session.getAttribute("information"));
%>
<%
    session.setMaxInactiveInterval(30);
%>
<%
    session.removeAttribute("information");
    if (session.getAttribute("information")== null){
        out.print("session object information non-existent ！");
    }
%>
</body>
</html>

8. session Three methods of timeout setting

a. stay java Set... In the code ：

session.setMaxInactiveInterval(300);  //session Without operation 300 Seconds out

b. In the project web.xml Set in ：

<!--  Set the value to 0、-1 It means never timeout , In minutes  -->
<session-config>
	<session-timeout>1</session-timeout>
</session-config>

c. Set in the application server

​ priority ：a > b > c

Code instance ：

<%@ page contentType="text/html;charset=UTF-8" language="java" pageEncoding="UTF-8" %>
<html>
<head>
    <title>Title</title>
</head>
<body style="font-size: 40px">
    <%! int number = 1;  // Login times of initialization interface %>
    <%
        Object obj = session.getAttribute("number"); //  obtain session Inside number Value 
        if (obj == null){   // Set up number Pair value of   // Set up session The value of the object 
            session.setAttribute("number",String.valueOf(number));
        }else{
            number = Integer.parseInt(obj.toString());
            number++;    // Count the number of visits 
            session.setAttribute("number",number);
        }
        session.setMaxInactiveInterval(2);
    %>
     You visit the... Of this website <%=number %> Users , welcome ！
</body>
</html>

9. session Object instances 

/***buy.jsp***/
<%@ page contentType="text/html;charset=UTF-8" language="java" pageEncoding="UTF-8" %>
<html>
<head>
    <title> customer </title>
</head>
<body>
<form action="goods.jsp">
    <b> Enter your name to connect to the first department store </b><br>
    <input type="text" name="name">
    <input type="submit" value=" Submit name ">
</form>
</body>
</html>


/***goods.jsp***/
<%@ page contentType="text/html;charset=UTF-8" language="java" pageEncoding="UTF-8" %>
<html>
<head>
    <title> The supermarket </title>
</head>
<body>
<%
    request.setCharacterEncoding("UTF-8");
    Object name = request.getParameter("name");
    session.setAttribute("name",name);
%>
<form action="account.jsp">
    <b> Please enter the goods you want to buy and connect to the checkout </b><br>
    <input type="text" name="goods">
    <input type="submit" value=" Submit goods ">
</form>
</body>
</html>


/***account.jsp***/
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> Settle accounts </title>
</head>
<body>
<%
    request.setCharacterEncoding("UTF-8");
    Object goods = request.getParameter("goods");
    session.setAttribute("goods",goods);
%>
<b> This is the checkout </b><br>
<b> The customer's name is ：</b><%=session.getAttribute("name") %><br>
<b> What products do customers buy ：</b><%=session.getAttribute("goods") %>
</body>
</html>

application object

1. Definition

​ Application It is a data access area shared by all online users . Server startup application The object is created , Until the web server shuts down or exceeds the scheduled time application The object will disappear automatically . Customers browse various web pages ,application It's all the same .

2. session And application The difference between

​ session The object is dedicated to each customer , Private , Store private variables

​ application The object is a shared data access area , Public storage of global variables

3. Method 

1. setAttribute(String name,Object o);// Set up application Object's attribute name and its attribute value 
2. getAttribute(String name);// Get the attribute value of the specified attribute name 
3. getAttributeNames();// obtain Enumeration Type of application An initial value of an object 
4. getServerInfo();// obtain servlet Current version information of the compiler 
5. getContext(String uripath);// Get the specified WebApplication Of application object 
6. getMimeType(String file);// obtain application Object specifies the MIME type 
7. getResource(String path);// obtain application Object specifies the url route 
8. getServlet(String name);// obtain application Object specified Servlet

4. access application Data in

1. establish application object 

application.setAttribute(" Variable name "," Variable content ")

2. obtain application The object is worth 

application.getAttribute(" Variable name ");
application.getAttributeNames();// The return is application The collection object of all object names in , The data type is array

3. Delete application object 

application.removeAttribute(" Variable name ");

example 1: Message board 

/***inputMessage.jsp***/
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> Input information </title>
</head>
<body>
<form action="checkMessage.jsp" method="post">
     Please enter a name ：<input type="text" name="name"><br>
     Please enter a title ：<input type="text" name="title"><br>
     Please enter the content ：<textarea name="message" cols="40" rows="10"></textarea><br>
    <input type="submit" value=" Leaving a message. ">
</form>
<form action="showMessage.jsp" method="post" id="form2">
    <input type="submit" value=" Check the message board ">
</form>
</body>
</html>


/***checkMessage.jsp***/
%@ page import="java.util.List" %>
<%@ page import="java.util.ArrayList" %>
<%@ page import="jdk.nashorn.internal.ir.CallNode" %>
<%@ page import="java.util.logging.SimpleFormatter" %>
<%@ page import="java.util.Calendar" %>
<%@ page import="java.text.SimpleDateFormat" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> Information processing </title>
</head>
<body>
<%!
   List<String> v = new ArrayList<String>();
   int i = 0;
%>
<%
    String datetime = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss").format(Calendar.getInstance().getTime());// Get system time 
%>
<%
    request.setCharacterEncoding("UTF-8");
    String name = request.getParameter("name");
    String title = request.getParameter("title");
    String message = request.getParameter("message");
%>
<%
    if(name == null || "".equals(name.trim())){
        name = " Net friend " + (int)(Math.random()*10000+10000); // When name by null Will output 5 Random number of digits 
    }
    if (title == null || "".equals(title.trim())){
        title = " nothing ";
    }
    if (message == null || "".equals(message.trim())){
        message = " nothing ";
    }
%>
<%
    i++;
    String str = " The first " + i + " floor " + ". Message sender :" + name + ". title :" + title + ". Content :" + message + ". Time :" + datetime + ".<hr>";
    v.add(str);
    application.setAttribute("message",v);
%>
 Message success ：<a href="inputMessage.jsp"> Return to the message board </a>
</body>
</html>

/***showMessage.jsp***/
<%@ page import="java.util.List" %>
<%@ page import="java.util.ArrayList" %>
<%@ page import="java.util.StringTokenizer" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> Message content </title>
</head>
<body>
<%
    Object o = application.getAttribute("message");
    if (o == null) {
        out.print(" No one has left a message yet ");
    } else {
        List<String> v = (ArrayList<String>) o;
        for (int i = v.size() - 1; i >= 0; i--) {
            StringTokenizer st = new StringTokenizer(v.get(i), ".");
            while (st.hasMoreElements()) {
                out.print(st.nextToken() + "<br>");
            }
        }
    }
%>
</body>
</html>

example 2： Page counters （ It needs to be improved ）

<%@ page import="java.util.StringTokenizer" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> Page counters </title>
</head>
<body style="font-size: 40px">
<%
    int i = 0;
    if (application.getAttribute("num") == null) {
        application.setAttribute("num", 1);
    } else {
        if (session.isNew()) { // Determine whether it is a new user 
            String str = application.getAttribute("num").toString();
            i = Integer.parseInt(str);
            i++;
            application.setAttribute("num", i);
        }
    }
%>
 You are the first <%=application.getAttribute("num") %> Visitors 
</body>
</html>

5. session Object and the application The difference between objects

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6. application Object instances 

/***chat.jsp***/
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> Chat </title>
</head>
<body>
<%request.setCharacterEncoding("UTF-8"); %>
<%
    if (application.getAttribute("information") == null) {
        application.setAttribute("information", "Start:");
        out.print((String) application.getAttribute("information"));
    }
    if (request.getParameter("information") != null) {
        if (request.getParameter("information").trim() == "end") { // Judge the end of the conversation , unsuccessful 
            application.removeAttribute("information");
            out.print(" End of conversation ！");
        }
        String information = request.getParameter("information");
        information = (String) application.getAttribute("information") + "<br>" + information; // Copy the previous conversation to application In the object 
        application.setAttribute("information", information);
        out.print((String) application.getAttribute("information"));
    }
%>
<form action="chat.jsp">
    <input type="text" name="information">
    <input type="submit" value=" send out ">
</form>
</body>
</html>

page object

1. Definition

​ a. page Object represents the running by jsp File generated class objects , This object is in jsp It's not often used in English

​ b. java.lang.Object class , have access to Object Class method

2. effect

​ Set to execute the response request of the current page Servlet Class , Only in jsp The page is legal .page The implied object essentially contains the present Servlet Variables referenced by interfaces , Can be seen as this Another name for

3. Method

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