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Cookie Technology & session Technology & ServletContext object
2022-07-06 07:05:00 【aigo-2021】
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
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