严重：处理请求期间发生异常：null java.lang.NullPointerException
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时间：2020-11-02 20:31:35 来源:igfitidea点击:
SEVERE: Exception occurred during processing request: null java.lang.NullPointerException
提问by Sourav
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:
我正在尝试在 Eclipse 中的 Struts2 中创建一个基本的登录/注册。我遇到了无法解决的异常，我尝试了过去几个小时：
<?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
网页.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
这是我得到的问题详细信息
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.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:
这是登录操作：
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;
}
}
采纳答案by 12dollar
Your
你的
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.
未初始化。它是 NULL。如果你想匹配一个空字符串，你必须先初始化它。
so change it to
所以把它改成
private String userId = "";
回答by Andrea Ligios
You are in deep water... :| By the way, in a nutshell:
你在深水里... :| 顺便说一句，简而言之：
Preventing NPE
预防 NPE
To prevent NPE when comparing strings, compare them with the known one:
为了防止在比较字符串时出现 NPE，请将它们与已知字符串进行比较：
if (userId.equals("")) { // throws NPE
if ("".equals(userId)) { // it's ok
In your code however you should check also null, so both are ok:
但是，在您的代码中，您还应该检查 null，因此两者都可以：
if (userId==null || userId.equals("")) {
The right place for this: Validation
正确的地方：验证
Now that they work, remove all this checks and put them in the validate()method, or in a validation.xmlfile, or use annotationsfor validating them. Struts supports all of this methods, and returns the INPUTresult when things go south.
现在它们可以工作了，删除所有这些检查并将它们放在validate()方法中，或者放在validation.xml文件中，或者使用注释来验证它们。Struts 支持所有这些方法，并在事情变得糟糕时返回INPUT结果。
Never put this kind of checks in an action method, it's the wrong place.
永远不要将这种检查放在动作方法中，这是错误的地方。
The right Struts2 way to handle authentication: Interceptor
Struts2 处理身份验证的正确方式：拦截器
Don't use actions to do this, but create an Authentication Interceptor, applying it to all the actions except the login/logout ones.
不要使用操作来执行此操作，而是创建一个身份验证拦截器，将其应用于除登录/注销之外的所有操作。
There is a full working example here.
这里有一个完整的工作示例。
回答by luck930101
Your private variable userIdis not initialized. This comment is correct.
However, you should write a set function
您的私有变量userId未初始化。这个评论是正确的。但是，您应该编写一个 set 函数
public void setUserId(String userId){
this.userId =userId;
}
to initialize your variable instead of
初始化你的变量而不是
private String userId = "";
I have the same problem as yours and this my solution.
我和你有同样的问题，这是我的解决方案。
