SEVERE: Exception occurred during processing request: null java.lang.NullPointerException

Question

I am trying to create a basic Login/Registration in Struts2 in eclipse. I am getting exceptions that I am unable to solve, I am trying it for last few hours:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC
   "-//Apache Software Foundation//DTD Struts Configuration 2.5//EN"
   "http://struts.apache.org/dtds/struts-2.5.dtd">

<struts>
    <include file="struts-default.xml"/>
    <package name="a" extends="struts-default">
        <action name="loginauth" class="com.project.loginreg.LoginAction" method="execute" >
           <result name="SUCCESS" type="redirect">
        <param name="location">/welcome.jsp</param>
        </result>
            <result name="ERROR">/login.jsp</result>
        </action>
    </package>
</struts>

Web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>Login_Reg</display-name>

<filter>
    <filter-name>struts2</filter-name>
<filter-class>
       org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter                
</filter-class>
</filter>

<filter-mapping>
    <filter-name>struts2</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

<welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>

Here is the problem details I am geting

Sep 17, 2015 4:54:41 PM org.apache.struts2.dispatcher.DefaultDispatcherErrorHandler error
SEVERE: Exception occurred during processing request: null
java.lang.NullPointerException
    at com.project.loginreg.LoginAction.execute(LoginAction.java:14)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at ognl.OgnlRuntime.invokeMethod(OgnlRuntime.java:870)
    at ognl.OgnlRuntime.callAppropriateMethod(OgnlRuntime.java:1293)
    at ognl.ObjectMethodAccessor.callMethod(ObjectMethodAccessor.java:68)
    at com.opensymphony.xwork2.ognl.accessor.XWorkMethodAccessor.callMethodWithDebugInfo(XWorkMethodAccessor.java:117)
    at com.opensymphony.xwork2.ognl.accessor.XWorkMethodAccessor.callMethod(XWorkMethodAccessor.java:108)
    at ognl.OgnlRuntime.callMethod(OgnlRuntime.java:1369)
    at ognl.ASTMethod.getValueBody(ASTMethod.java:90)
    at ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:212)
    at ognl.SimpleNode.getValue(SimpleNode.java:258)
    at ognl.Ognl.getValue(Ognl.java:494)
    at ognl.Ognl.getValue(Ognl.java:458)
    at com.opensymphony.xwork2.ognl.OgnlUtil$2.execute(OgnlUtil.java:309)
    at com.opensymphony.xwork2.ognl.OgnlUtil.compileAndExecute(OgnlUtil.java:340)
    at com.opensymphony.xwork2.ognl.OgnlUtil.getValue(OgnlUtil.java:307)
    at com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:423)
    at com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:287)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:250)
    at org.apache.struts2.interceptor.DeprecationInterceptor.intercept(DeprecationInterceptor.java:41)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:256)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:167)
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:265)
    at org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:76)
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:138)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:229)
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:229)
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:191)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:73)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at org.apache.struts2.interceptor.DateTextFieldInterceptor.intercept(DateTextFieldInterceptor.java:125)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:91)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:253)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:100)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:145)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:171)
    at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:139)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:193)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:189)
    at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
    at org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:54)
    at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:564)
    at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:81)
    at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:99)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:462)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:562)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:395)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:250)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:188)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:302)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

Heres the LoginAction:

package com.project.loginreg;

import com.opensymphony.xwork2.ActionSupport;

public class LoginAction extends ActionSupport{

    private static final long serialVersionUID = 1L;
    private String userId;
    private String password;

    private Boolean error;

    public String execute(){
        if (userId.equals("")) {
            addActionError("Please Enter user id.");
            error = true;
        }
        else if(password.equals("")){
            addActionError("Please Enter Password.");
            error = true;
        }
         else if(!userId.equalsIgnoreCase(password)) {
             addActionError("Invalid userid or password.");
             error = true;
         } else {
             error = false;
         }
        if (error) {
            return ERROR;
        } else {
            return SUCCESS;
        }   
    }

    public String getUserId() {
        return userId;
    }

    public void setUserId(String userId) {
        this.userId = userId;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

can you post the LoginAction.java and what's on the line#14? — Karthik R, Sep 17 '15 at 11:38
Please post your JSP as well. The userId you are mapping is not being received. — Karthik R, Sep 17 '15 at 11:51
Your NPE is coz of your null userName. This can be avoided by initializing but that's not your problem I suppose — Karthik R, Sep 17 '15 at 11:54
@KarthikR After doing as u said,that exception has been removed but I am getting another one.... – Sourav 48 secs ago edit org.apache.struts2.dispatcher.Dispatcher warn WARNING: Could not find action or result: /Login_Reg/loginAuth.action There is no Action mapped for namespace [/] and action name [loginAuth] associated with context path [/Login_Reg]. - [unknown location] — Sourav, Sep 17 '15 at 11:57
@KarthikR Yes ... I mean "Login_Reg" as project name.. and then action mapping "loginauth.action" — Sourav, Sep 17 '15 at 12:04
@KarthikR No result defined for action com.project.loginreg.LoginAction and result error- what may be the reason for this prob? — Sourav, Sep 17 '15 at 12:04
`I am trying it for last few years` duude, you really need some help then :| — Andrea Ligios, Sep 17 '15 at 12:06
@AndreaLigios omg!! :D lolz... sorry , I wanted to write Hours. — Sourav, Sep 17 '15 at 12:09
What you should know about nullpointerexception, it tells you that you have something wrong in the code or data supplied into it that doesn't work and if you prevent it in the code using some techniques then it will not throw the exception but the program does not become working. — Roman C, Sep 24 '15 at 11:59

score 2 · Accepted Answer · answered Sep 17 '15 at 11:50

2

Your

private String userId

is not initialized. It's NULL. If you want to match against an empty string you'd have to initialize it first.

so change it to

private String userId = "";

answered Sep 17 '15 at 11:50

12dollar

645
3
17

After doing as u said,that exception has been removed but I am getting another one.... – Sourav Sep 17 '15 at 11:55
org.apache.struts2.dispatcher.Dispatcher warn WARNING: Could not find action or result: /Login_Reg/loginAuth.action There is no Action mapped for namespace [/] and action name [loginAuth] associated with context path [/Login_Reg]. - [unknown location] – Sourav Sep 17 '15 at 11:56

score 2 · Answer 2 · edited Jun 20 '20 at 09:12

You are in deep water... :| By the way, in a nutshell:

Preventing NPE

To prevent NPE when comparing strings, compare them with the known one:

if (userId.equals("")) { // throws NPE
if ("".equals(userId)) { // it's ok

In your code however you should check also null, so both are ok:

if (userId==null || userId.equals("")) {

The right place for this: Validation

Now that they work, remove all this checks and put them in the validate() method, or in a validation.xml file, or use annotations for validating them. Struts supports all of this methods, and returns the INPUT result when things go south.

Never put this kind of checks in an action method, it's the wrong place.

The right Struts2 way to handle authentication: Interceptor

Don't use actions to do this, but create an Authentication Interceptor, applying it to all the actions except the login/logout ones.

There is a full working example here.

score 0 · Answer 3 · edited Nov 20 '17 at 02:36

0

Your private variable userId is not initialized. This comment is correct. However, you should write a set function

public void setUserId(String userId){
    this.userId =userId;
}

to initialize your variable instead of

private String userId = "";

I have the same problem as yours and this my solution.

edited Nov 20 '17 at 02:36

roelofs

2,132
20
25

answered Nov 20 '17 at 01:49

luck930101

1
1

SEVERE: Exception occurred during processing request: null java.lang.NullPointerException

3 Answers3

Preventing NPE

The right place for this: Validation

The right Struts2 way to handle authentication: Interceptor