为什么是java.lang.NullPointerException

小第刚学,出现问题,请指教
这是检查登录时checklogin.jsp代码
<%@ page contentType="text/html; charset=GBK" %>
<html>
<head>
<title>
checklogin
</title>
</head>
<jsp:useBean id="checkloginBeanId" scope="session" class="login.CheckloginBean" />
<jsp:setProperty name="checkloginBeanId" property="*" />
<body bgcolor="#ffffff">
<%
String name=request.getParameter("name");
String password=request.getParameter("password");
if(name.equals("laocai"))
{
%>
<jsp:forward page="success.jsp">
<jsp:param name="user" value="<%=name%>"/>
</jsp:forward>
<%
}
else
{
%>
<jsp:forward page="login.jsp">
<jsp:param name="user" value="<%=name%>"/>
</jsp:forward>
<%
}
%>
</body>
</html>
这是登录成功时的success.jsp代码
<%@ page contentType="text/html; charset=GBK" %>
<html>
<head>
<title>
success
</title>
</head>
<jsp:useBean id="successBeanId" scope="session" class="login.SuccessBean" />
<jsp:setProperty name="successBeanId" property="*" />
<body bgcolor="#ffffff">
登录成功
<br>
欢迎你
<%=request.getParameter("name")%>
</body>
</html>
这是错误信息
message Internal Server Errordescription The server encountered an internal error (Internal Server Error) that prevented it from fulfilling this request.exception java.lang.NullPointerException
 at org.apache.jsp.checklogin$jsp._jspService(checklogin$jsp.java:97)
 at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:107)
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
 at org.apache.jasper.servlet.JspServlet$JspServletWrapper.service(JspServlet.java:201)
 at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:381)
 at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:473)
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
 at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:243)
 at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
 at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
 at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
 at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:190)
 at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
 at org.apache.catalina.valves.CertificatesValve.invoke(CertificatesValve.java:246)
 at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
 at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
 at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
 at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2347)
 at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180)
 at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
 at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:170)
 at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
 at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:170)
 at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:564)
 at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
 at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
 at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174)
 at org.apache.catalina.core.StandardPipeline.invokeNext(StandardPipeline.java:566)
 at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:472)
 at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:943)
 at org.apache.catalina.connector.http.HttpProcessor.process(HttpProcessor.java:1027)
 at org.apache.catalina.connector.http.HttpProcessor.run(HttpProcessor.java:1125)
谢谢

解决方案 »

  1.   

    估计是 
    String name=request.getParameter("name");
    String password=request.getParameter("password");
    if(name.equals("laocai")) //这里，因为没有接收到name参数，所以name == null，调用equals会报Null错误
      

  2.   

    String name=request.getParameter("name");
    String password=request.getParameter("password");最好包装一下
    import javax.servlet.http.*;public class Util
    {
      public static String convertNull2Empty(String param){
        
        return (param == null)? "":param;
      }
    }----------------
    String name = Util.convertNull2Empty(request.getParameter("name"));
      

  3.   

    at org.apache.jsp.checklogin$jsp._jspService(checklogin$jsp.java:97)
    checklogin$jsp.java:97
    找到这行的代码是什么