java - Javaservlet nullpointerexception -
i'm trying make simple login screen. has check password , username. there default user, set in init(). weird thing is, it's still giving me nullpointerexception on rd.forward();
explain? i'm sorry bad english, let me know if have elaborate more.
package servlets; import java.io.bufferedreader; import java.io.file; import java.io.filereader; import java.io.ioexception; import java.io.printwriter; import java.sql.connection; import java.sql.drivermanager; import java.sql.sqlexception; import java.util.arraylist; import java.util.scanner; import javax.servlet.filterconfig; import javax.servlet.requestdispatcher; import javax.servlet.servletconfig; import javax.servlet.servletexception; import javax.servlet.http.httpservlet; import javax.servlet.http.httpservletrequest; import javax.servlet.http.httpservletresponse; import classes.user; public class loginservlet extends httpservlet { arraylist<user> alleusers = new arraylist<>(); private string defaultuser="", defaultpassword=""; private user userding; public void init(servletconfig config) throws servletexception{ super.init(config); defaultuser = config.getinitparameter("defaultuser"); defaultpassword = config.getinitparameter("defaultpassword"); user userding = new user(defaultuser, defaultpassword); } protected void dopost(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception { string = req.getparameter("back"); string b = req.getparameter("username"); string c = req.getparameter("password"); object o = getservletcontext().getattribute("arraylist"); requestdispatcher rd = null; if (a.equals("register")) { rd = req.getrequestdispatcher("registerscherm.jsp"); } if (a.equals("login")) { system.out.println(b + " "+ c); if(!b.equals(null) && !c.equals(null)){ if (o instanceof arraylist) { alleusers = (arraylist) o; alleusers.add(userding); if (alleusers != null) { (user u : alleusers) { if (b.equals(u.getusername()) && c.equals(u.getpassword())) { getservletcontext().setattribute("naam", b); rd = req.getrequestdispatcher("ingelogdscherm.jsp"); break; } else { rd = req.getrequestdispatcher("loginscherm.jsp"); } } } } }else{ rd = req.getrequestdispatcher("loginscherm.jsp"); } } rd.forward(req, resp); //it gives error on forward } } here's loginscreen jsp page:
<body> <% string username = ""; (cookie c : request.getcookies()) { if (c.getname().equals("username")) { username = c.getvalue(); break; } } %> <div id="account"> <div id="inputbox"> <form action="loginservlet.do" method="post"> <input class="ltf" type="text" name="username" value="<%= username %>" /><br/> <input class="ltf" type="password" name="password" /><br/> <input type="submit" name="back" value="login" /> <input type="submit" name="back" value="register" /> </form> </div>
okay think fixed it. removed of guards, helped. i'm still confused why didnt go through them, works now. thanks!
if value of a not equal "login" or "register" rd remains null rd.forward(req, resp); give nullpointerexception.
can debug printing value of a or can add rd.forward(req, resp); wherever use req.getrequestdispatcher("name.jsp"); below :
package servlets; import java.io.bufferedreader; import java.io.file; import java.io.filereader; import java.io.ioexception; import java.io.printwriter; import java.sql.connection; import java.sql.drivermanager; import java.sql.sqlexception; import java.util.arraylist; import java.util.scanner; import javax.servlet.filterconfig; import javax.servlet.requestdispatcher; import javax.servlet.servletconfig; import javax.servlet.servletexception; import javax.servlet.http.httpservlet; import javax.servlet.http.httpservletrequest; import javax.servlet.http.httpservletresponse; import classes.user; public class loginservlet extends httpservlet { arraylist<user> alleusers = new arraylist<>(); private string defaultuser="", defaultpassword=""; private user userding; public void init(servletconfig config) throws servletexception{ super.init(config); defaultuser = config.getinitparameter("defaultuser"); defaultpassword = config.getinitparameter("defaultpassword"); user userding = new user(defaultuser, defaultpassword); } protected void dopost(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception { string = req.getparameter("back"); string b = req.getparameter("username"); string c = req.getparameter("password"); object o = getservletcontext().getattribute("arraylist"); requestdispatcher rd = null; if (a.equals("register")) { rd = req.getrequestdispatcher("registerscherm.jsp"); rd.forward(req, resp); } if (a.equals("login")) { system.out.println(b + " "+ c); if(!b.equals(null) && !c.equals(null)){ if (o instanceof arraylist) { alleusers = (arraylist) o; alleusers.add(userding); if (alleusers != null) { (user u : alleusers) { if (b.equals(u.getusername()) && c.equals(u.getpassword())) { getservletcontext().setattribute("naam", b); rd = req.getrequestdispatcher("ingelogdscherm.jsp"); rd.forward(req, resp); break; } else { rd = req.getrequestdispatcher("loginscherm.jsp"); rd.forward(req, resp); } } } } }else{ rd = req.getrequestdispatcher("loginscherm.jsp"); rd.forward(req, resp); } } } }
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