一个简单的用户管理系统,输入用户名和密码后,出现了如下问题:
u=wanglip=123java.lang.NullPointerException
at com.model.UserBeanCL.usercheck(UserBeanCL.java:121)
at com.control.loginCLservLet.doGet(loginCLservLet.java:36)
at com.control.loginCLservLet.doPost(loginCLservLet.java:64)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:849)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:454)
at java.lang.Thread.run(Thread.java:619)其中 loginCLservelet.java 类如下:
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//接受用户名和密码
String u=request.getParameter("username");
u=new String(u.getBytes("ISO-8859-1"),"gb2312");
String p=request.getParameter("passwd");
//System.out.print("这一个模型的例子");
System.out.print("u="+u+"p="+p);
//定义一个类,调用UserBeanCLl类方法
UserBeanCL ubc =new UserBeanCL();
//验证信息
if(ubc.usercheck(u,p)){
System.out.println("这一个模型的例子");
request.getRequestDispatcher("WL.jsp").forward(request,response);
}else{
request.getRequestDispatcher("login.jsp").forward(request, response);
}
请哪位高人指点一下
u=wanglip=123java.lang.NullPointerException
at com.model.UserBeanCL.usercheck(UserBeanCL.java:121)
at com.control.loginCLservLet.doGet(loginCLservLet.java:36)
at com.control.loginCLservLet.doPost(loginCLservLet.java:64)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:849)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:454)
at java.lang.Thread.run(Thread.java:619)其中 loginCLservelet.java 类如下:
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//接受用户名和密码
String u=request.getParameter("username");
u=new String(u.getBytes("ISO-8859-1"),"gb2312");
String p=request.getParameter("passwd");
//System.out.print("这一个模型的例子");
System.out.print("u="+u+"p="+p);
//定义一个类,调用UserBeanCLl类方法
UserBeanCL ubc =new UserBeanCL();
//验证信息
if(ubc.usercheck(u,p)){
System.out.println("这一个模型的例子");
request.getRequestDispatcher("WL.jsp").forward(request,response);
}else{
request.getRequestDispatcher("login.jsp").forward(request, response);
}
请哪位高人指点一下
解决方案 »
- [菜鳥]java poi excel 怎樣拿圖中這個資料
- 关于readline()的问题
- 有没有什么办法能轻易地知道什么时候该加入什么jar包?
- 这个问题什么意思?
- 有谁知道:点击按钮后,关闭该窗口,再弹出另一个窗口的方法?
- 请问关于string类的问题,郁闷啊
- jdbc连数据库时的url中的“:”是什么意思?
- socket如何实现发送信息30秒后未收到应答信息立即重发?再连续发送3次后仍未得到应答则停发,请问该如何实现?
- 请问如何在客户端未安装jre插件时还能使applet正常显示?
- 关于视频的问题!(急呀!)
- 新手求助:用SWT遇见的问题,麻烦高手给予解决
- 请问使用swt做的ole控件怎么绑定到数据库中
而一般报java.lang.NullPointerException的原因有以下几种:
1字符串变量未初始化;
2接口类型的对象没有用具体的类初始化,比如:
List lt;会报错
List lt = new ArrayList();则不会报错了
3当一个对象的值为空时,你没有判断为空的情况。
UserBeanCL ubc =new UserBeanCL();应该判断下ubc是否创建成功
这个方法里面的内容 没问题吗??????