使用request.getSession()时出现NullPointerException错误

[黑土墨]

我做了一个简单的注册登录系统，登录时想把用户名保存到session中，但总是出现这样的错误：
HTTP Status 500 -

type Exception report
message
description The server encountered an internal error () that prevented it from fulfilling this request.
exception
java.lang.NullPointerException
com.zzk.regandlogin.action.LoginAction.execute(LoginAction.java:63)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:585)
com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:441)
com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:280)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:243)
com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:165)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:252)
org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:68)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:122)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:195)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:195)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:179)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:94)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:235)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:89)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:130)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:267)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:126)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:138)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:165)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:179)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:176)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)
org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:488)
org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.33 logs.
Apache Tomcat/6.0.33

LoginAction.java中第63行的代码是：HttpSession session = request.getSession();
不得到session时程序是正确的。

以下是LoginAction.java中的全部代码：
package com.zzk.regandlogin.action;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

import com.opensymphony.xwork2.ActionContext;
import com.opensymphony.xwork2.ActionSupport;
import com.opensymphony.xwork2.ModelDriven;
import com.zzk.regandlogin.dao.UserDAOImpl;
import com.zzk.regandlogin.dao.interfaces.UserDAO;
import com.zzk.regandlogin.model.User;

public class LoginAction extends ActionSupport implements ModelDriven<User> {

private static final long serialVersionUID = -1655622871625965987L;

private User user = new User();
private HttpServletRequest request;

public HttpServletRequest getRequest() {
return request;
}


public void setRequest(HttpServletRequest request) {
this.request = request;
// this.request = (HttpServletRequest)ActionContext.getContext().getSession().get(ServletActionContext.HTTP_REQUEST);
}

public User getModel() {
return user;
}

public String execute() throws Exception{
UserDAO userDAO = new UserDAOImpl();
Object obj = ActionContext.getContext().getSession().get("validation_code");
String validationCode = (obj != null) ? obj.toString() : "";

if(!validationCode.equalsIgnoreCase(user.getValidationCode())){
if(validationCode != null){
this.addActionError("验证码输入错误！");
return INPUT;
}
}

if(!userDAO.validateUser(user)){
this.addActionError("用户名或密码错误！");
return INPUT;
}


HttpSession session = request.getSession();
session.setAttribute("username", user.getUsername());
session.setMaxInactiveInterval(60 * 60 * 3);
return SUCCESS;
}
}

user.getUsername()可以得到值。
到底是哪出错了，求解……

[wrweirong]

菜鸟路过，友情支持！

[Cactus_hxk]

HttpServletRequest request = ServletActionContext.getRequest();这样试试！

[kangchongmian]

HttpSession session = request.getSession();
这句话改成：Map<String,Object> session = ActionContext.getContext().getSession();
试试！

[大大大宝剑]

[Quote=引用 3 楼 zongzhankui 的回复:]

两种方法：
1.构造函数
public LoginAction(){
this.request = ServletActionContext.getRequest();
session = request.getSession();
}
2.接口
实现ServletRequestAware接口
[/Quote]
这个好

[ylovep]

楼主要确保已经讲值放入到session中

[黑土墨]

两种方法：
1.构造函数
public LoginAction(){
this.request = ServletActionContext.getRequest();
session = request.getSession();
}
2.接口
实现ServletRequestAware接口

[wangshiyang]

HttpSession session = getRequest.getSession();

[wangshiyang]

不对！ 你的request都没初始化！ 那个setRequest()方法都没执行，你先初始化再说吧！

[py1025677845]

HttpServletRequest 不是HttpSession 、

[javabugsmaker]

因为request是空的。。。

HttpServletRequest request = ServletActionContext.getRequest();
HttpSession session = request.getSession();

这样就行了。。

[crazywolf]

HttpServletRequest rq = ServletActionContext.getRequest();

[qer231]

12楼的办法真好！

[neal_niqiu]

ServletActionContext 这个东西根本就没有，一群跟风的

[xiangfu_txe]

我刚好遇到这个问题了，哈哈，在这里参考了一下大家的意见后，发觉真的是初始化问题，我是strut2 的action中定义了，原来是private javax.servlet.http.HttpServletRequest ；后来改成private javax.servlet.http.HttpServletRequest request = ServletActionContext.getRequest(); 就没问题了，发表一下意见，希望有和我一样的菜鸟也可以分享一下。。