httpsurlconnection - How do the Java classes CookieHandler and CookieManager work? -

the way can code programmatically login url using cookiehandler.setdefault(new cookiemanager);. fine, want understand how cookie being maintained between each new httpsurlconnection.

can please show how make code below log gmail account without having use cookiehandler.setdefault(new cookiemanager);? thanks.

**notes:
- substitute own email , password.
-cookiehandler.setdefault(new cookiemanager); commented out in code below.

public class gmailapp {      private list<string> cookies;     private httpsurlconnection conn;      public static void main(string[] args) throws exception {          string url = "https://accounts.google.com/serviceloginauth";         string gmail = "https://mail.google.com/mail/";          gmailapp http = new gmailapp();          // cookiehandler.setdefault(new cookiemanager());          string page = http.getpagecontent(url);         string postparams = http.getformparams(page, "myemail@gmail.com", "mypassword");         http.sendpost(url, postparams);          string result = http.getpagecontent(gmail);         system.out.println(result);     }      private void sendpost(string url, string postparams) throws exception {          url obj = new url(url);         conn = (httpsurlconnection) obj.openconnection();         conn.setdooutput(true);         dataoutputstream wr = new dataoutputstream(conn.getoutputstream());         wr.writebytes(postparams);         wr.flush();         wr.close();          int responsecode = conn.getresponsecode();         system.out.println("\nsending 'post' request url : " + url);         system.out.println("post parameters : " + postparams);         system.out.println("response code : " + responsecode);          bufferedreader in =                 new bufferedreader(new inputstreamreader(conn.getinputstream()));         string inputline;         stringbuffer response = new stringbuffer();          while ((inputline = in.readline()) != null) {             response.append(inputline);         }         in.close();     }      private string getpagecontent(string url) throws exception {          url obj = new url(url);         conn = (httpsurlconnection) obj.openconnection();         conn.setrequestmethod("get");         conn.setusecaches(false);         if (cookies != null) {             (string cookie : this.cookies) {                 conn.addrequestproperty("cookie", cookie.split(";", 1)[0]);             }         }         int responsecode = conn.getresponsecode();         system.out.println("\nsending 'get' request url : " + url);         system.out.println("response code : " + responsecode);          bufferedreader in =                 new bufferedreader(new inputstreamreader(conn.getinputstream()));         string inputline;         stringbuffer response = new stringbuffer();          while ((inputline = in.readline()) != null) {             response.append(inputline);         }         in.close();         setcookies(conn.getheaderfields().get("set-cookie"));         return response.tostring();     }      public string getformparams(string html, string username, string password)             throws unsupportedencodingexception {          system.out.println("extracting form's data...");          document doc = jsoup.parse(html);          element loginform = doc.getelementbyid("gaia_loginform");         elements inputelements = loginform.getelementsbytag("input");         list<string> paramlist = new arraylist<string>();         (element inputelement : inputelements) {             string key = inputelement.attr("name");             string value = inputelement.attr("value");              if (key.equals("email"))                 value = username;             else if (key.equals("passwd"))                 value = password;             paramlist.add(key + "=" + urlencoder.encode(value, "utf-8"));         }          stringbuilder result = new stringbuilder();         (string param : paramlist) {             if (result.length() == 0) {                 result.append(param);             } else {                 result.append("&" + param);             }         }         return result.tostring();     }      public void setcookies(list<string> cookies) {         this.cookies = cookies;     }  }  

when set default cookiehandler statically via java.net.cookiehandler.setdefault(), current , futute httpurlconnections (via underlying http client classes) check existence of default cookie handler, , finding use retrieve cookies requests, , store new cookies set/returned. provides static cookie-jar long want maintain cookies across requests. sure set desired cookiepolicy, or java.net.cookiepolicy.accept_original_server default.

note there's few issues code:

cookie.split(";", 1)[0] 

this split won't anything, want cookie.split(";", 2)[0] (1->2) if want truncate string first semicolon onwards.

also, calling setcookies after requests - need capture cookies in response post login.