1. What is Cookie?
Cookie is actually a text file written by the Web server on the user's hard disk when the user accesses the website through a browser.
It contains some user information, which is stored in the form of key-value pairs
2. Typical applications using cookies
The following uses Cookie technology, which we often see.
3. Cookie Programming
Setpath is used to set the storage location.
The cookie constructor has two parameters, both of which are of the string type. They are preceded by a "key" and followed by a "value"
Setmaxage: Set the validity period. getmaxage gets the validity period.
Send Response. Add (...), that is, save the cookie object
Read Request. getcookies ()
Cookie. setvalue ()
4. Cookie Defects
5. programming example
Foreground cookieinput.htm
<HTML>
Background
String processing class
Package webbook. util; public class stringutil {/*** determines whether the input string parameter is null. * @ Param ARGs the input string * @ return true/false */public static Boolean validatenull (string ARGs) {If (ARGs = NULL | args. length () = 0) {return true;} else {return false;}/*** determines whether the input string parameter is null or a "null" character, if yes, the target parameter is returned. If not, the source parameter is returned. */Public static string chanagenull (string source, string target) {If (Source = NULL | source. length () = 0 | source. equalsignorecase ("null") {return target;} else {return source ;}/ ***** filter <,>, \ n characters. * @ Param input the character to be filtered * @ return the string to be filtered */public static string filterhtml (string input) {If (input = NULL) {return NULL ;} if (input. length () = 0) {return input;} input = input. replaceall ("&", "&"); input = input. replaceall ("<", "<"); input = input. replaceall (">", ">"); input = input. replaceall ("", ""); input = input. replaceall ("'", "'"); input = input. replaceall ("\" "," "); Return input. replaceall ("\ n", "<br> ");}}
Servlet for Cookie setting
Package webbook. chapter6; import Java. io. ioexception; import Java. io. printwriter; import Java. text. simpledateformat; import Java. util. date; import webbook. util. stringutil; import javax. servlet. servletexception; import javax. servlet. HTTP. cookie; import javax. servlet. HTTP. httpservlet; import javax. servlet. HTTP. httpservletrequest; import javax. servlet. HTTP. httpservletresponse; public class setcookiesservlet exte NDS httpservlet {Private Static final long serialversionuid = response; Public void doget (httpservletrequest request, httpservletresponse response) throws servletexception, ioexception {dopost (request, response );} public void dopost (httpservletrequest request, httpservletresponse response) throws servletexception, ioexception {string output = NULL; string username = request. getparameter (" Username "); If (! Stringutil. validatenull (username) {cookie cookie1 = new cookie ("username", stringutil. filterhtml (username); // The cookie is valid for one month cookie1.setmaxage (24*60*60*30 ); simpledateformat SDF = new simpledateformat ("yyyy-mm-dd"); cookie cookie2 = new cookie ("lasttime", SDF. format (new date (); cookie2.setmaxage (24*60*60*30); response. addcookie (cookie1); response. addcookie (cookie2); Output = "the current Logon Time and user name have been written To the cookie. <Br> <a href = \ "/webproject3/servlet/getcookies \"> View cookies </a> ";} The else {output =" username is blank. Please enter it again. <Br> <a herf = \ "/webproject3/cookieinput.htm \"> enter the user name </a> ";} response. setcontenttype ("text/html; charset = UTF-8"); printwriter out = response. getwriter (); out. println ("<HTML>"); out. println ("
Servlet for obtaining cookie
Package webbook. chapter6; import Java. io. ioexception; import Java. io. printwriter; import javax. servlet. servletexception; import javax. servlet. HTTP. cookie; import javax. servlet. HTTP. httpservlet; import javax. servlet. HTTP. httpservletrequest; import javax. servlet. HTTP. httpservletresponse; public class getcookiesservlet extends httpservlet {Private Static final long serialversionuid = response; Public void doget (httpservletrequest request, response) throws servletexception, ioexception {dopost (request, response );} public void dopost (httpservletrequest request, httpservletresponse response) throws servletexception, ioexception {response. setcontenttype ("text/html; charset = UTF-8"); printwriter out = response. getwriter (); out. println ("<HTML>"); out. println ("
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