java.lang.NullPointerException,该怎么解决
日期：2014-05-20 浏览次数：20876 次
java.lang.NullPointerException
<%@ page contentType= "text/html;charset=gb2312 " import= "java.sql.* "%>
<%@ page pageEncoding= "gb2312 " %>
<% request.setCharacterEncoding( "gb2312 "); %>
<jsp:useBean id= "sqlBean " class= "BYSJ.sqldata ">
</jsp:useBean> <html>
<html> <head> <title> </title> </head>
<body>
<% String username=request.getParameter( "username ");
String pwd=request.getParameter( "pwd "); //smt=conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_UPDATABLE);
String sql= "select * from user where username= ' "+username+ " ' and password= ' "+pwd+ " ' ";
ResultSet rs=sqlBean.executeQuery(sql);
if(!rs.next())
{
String errmsg= "error1 ";
response.sendRedirect( "login.jsp?errmsg= "+errmsg);
return;
}
request.getSession(true);
String chk= "true ";
session.putValue( "Enter ",chk);
session.putValue( "username ",rs.getString( "username "));
response.sendRedirect( "manage.jsp ");
%>
</body> </html>
这段代码怎么出现java.lang.NullPointerException
org.apache.jsp.BYSJ.logincheck_jsp._jspService(logincheck_jsp.java:65)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
------解决方案--------------------
你输出一下看username和pwd的值是否得到了？
------解决方案--------------------
把你的SQL输出，到你的数据库客户端执行一下，看看是什么结果
<%@ page contentType= "text/html;charset=gb2312 " import= "java.sql.* "%>
<%@ page pageEncoding= "gb2312 " %>
<% request.setCharacterEncoding( "gb2312 "); %>
<jsp:useBean id= "sqlBean " class= "BYSJ.sqldata ">
</jsp:useBean> <html>
<html> <head> <title> </title> </head>
<body>
<% String username=request.getParameter( "username ");
String pwd=request.getParameter( "pwd "); //smt=conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_UPDATABLE);
String sql= "select * from user where username= ' "+username+ " ' and password= ' "+pwd+ " ' ";
ResultSet rs=sqlBean.executeQuery(sql);
if(!rs.next())
{
String errmsg= "error1 ";
response.sendRedirect( "login.jsp?errmsg= "+errmsg);
return;
}
request.getSession(true);
String chk= "true ";
session.putValue( "Enter ",chk);
session.putValue( "username ",rs.getString( "username "));
response.sendRedirect( "manage.jsp ");
%>
</body> </html>
这段代码怎么出现java.lang.NullPointerException
org.apache.jsp.BYSJ.logincheck_jsp._jspService(logincheck_jsp.java:65)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
------解决方案--------------------
你输出一下看username和pwd的值是否得到了？
------解决方案--------------------
把你的SQL输出，到你的数据库客户端执行一下，看看是什么结果
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