Cookie Technology & session Technology & ServletContext object

One 、Cookie technology

Http The agreement has one feature , Namely No state , The data of each request response is not persisted . But I'm doing something Web When needed , It is necessary to record the user's status .

Cookie Technology can record some user information on the client . adopt ServletAPI Provided in Cookie class , Data can be stored in the client cookie In file , When sending a request ,cookie The contents of the file are contained in http In request .

Realize data passing Cookie Store on client , Create on the server side Cookie Class object , Encapsulate data into Cookie In the object , adopt response Object will Cookie Object responds back to the client , The client will automatically Cookie The data of is stored in the folder specified by the client Cookie In file .

for example ： Visit one TestServlet1 Send a name Store to client ：

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebServlet("/text1.do")
public class TestServlet1 extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // take tom name   Store to access this Servlet On the client side of 
        Cookie cookie = new Cookie("name1","tom");
        cookie.setMaxAge(60*60*24);
        resp.addCookie(cookie);
        Cookie cookie1 = new Cookie("name2","jack");
        cookie1.setMaxAge(60*60*24);
        resp.addCookie(cookie1);
        Cookie cookie2 = new Cookie("password","123");
        cookie2.setMaxAge(60*60*24);
        resp.addCookie(cookie2);
    }
}

Access in browser http:localhost:8080/emp/text1.do    View the stored Cookie data

You can visit a site , Get the... Of this site in the request Cookie data （ Client's ）

@WebServlet("/text2.do")
public class TestServlet2 extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse resp) throws
ServletException, IOException {
    // get   Client stored Cookie
        Cookie[] cookies = request.getCookies();
        for(Cookie cookie:cookies){
            System.out.println(cookie.getName()+","+cookie.getValue());
        }
    }
}

Two 、Session technology

Session Is the meaning of conversation , A session object representing the client and server , An object stored on the server .

When the client accesses the server , A session object will be created on the server , When the client accesses the server again , This session object is still used , No request response is generated within the validity of the session object , The session object will be destroyed ,tomcat Of session The default validity period of is 20 minute

There is a hash table storing session objects on the server （ Hashtable ）, When the browser accesses the server , The server reads the browser Cookie Zhongcun Stored session id.

3、 ... and 、Session Object lifecycle

because Session It has a long life cycle , Can be directed to Session Store some data in , Then the life cycle of these data is equivalent to session Life week of period , For example, how long does the login status need to be saved ？ As long as there is a request response operation , You need to save the login status .

How to talk to Session Medium storage data ：

HttpSession The interface provides setAttribute Method , Can be directed to Session Object to store data .

Store the data

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.io.IOException;
@WebServlet("/text1.do")
public class TestServlet1 extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse resp) throws ServletException, IOException {
        // towards Session Object   full name tom
        // First, get session object 
        HttpSession session = request.getSession();
        //session Object encapsulates a Map object , Stored data in Map in , Generally speaking, it is stored in Session Properties of 
        session.setAttribute("name1","tom");//key,value Form storage of 
    }
}

get data

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.io.IOException;
@WebServlet("/text2.do")
public class TestServlet2 extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse resp) throws
ServletException, IOException {
        // obtain Session Data in 
        HttpSession session = request.getSession();
        System.out.println(session.getAttribute("name1"));
    }
}

 get Session data , First visit text1.do, Revisit text2.do

Four 、 Set up Session The period of validity

stay web.xml in , Set up session The period of validity , The unit is minutes

<session-config>
    <session-timeout>1</session-timeout><!-- Set to 1 minute -->
</session-config>

Is there any request response within the validity period ,Session Be destroyed

Of course , You can also call HttpSession Methods , Give Way Session Object invalidation

// Give Way session invalid 
session.invalidate();

session Invalidation and destruction are different ,session The attribute value cannot be obtained after expiration , Nor can it fail again , Can't do these operations , but session Object still exists ;session The destruction of objects is Session The object doesn't exist , wipe out .

5、 ... and 、ServletContext object

ServletContext yes Servlet Context object , Also called application context object . stay Web The server （tomcat） Startup time ServletContext Object created ,Web When the server is destroyed ,ServletContext Object destroyed .

ServletContext Object lifecycle Longer than Session

Can be directed to ServletContext Object to store some data , The life cycle of data is related to ServletContext The life cycle is the same . through setAttribute and getAttribute Method to store and obtain

reflection ：

What kind of data exists Session in ？ What kind of data exists ServletContext in ？

The data shared by each page is stored in Session in ; Data shared by all users is stored in ServletContext in