java.lang.NullPointerException
at conn.UserBeanCl.CheckUser(UserBeanCl.java:47)
at controller.LoginClServlet.doGet(LoginClServlet.java:49)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
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:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
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.Http11AprProcessor.process(Http11AprProcessor.java:879)
at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:610)
at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1777)
at java.lang.Thread.run(Thread.java:619)
运行检查出错

定位错误地方：

public boolean CheckUser(String u,String p){
boolean b=false;
//到数据库去验证用户


try{
ct=new Connjdbc().getConn();
//创建statement
sm=ct.createStatement();
//查询
rs=sm.executeQuery("select PWD from USERNAME WHERE NAME='"+u+"'");
//根据判断结果
if(rs.next()){
if(rs.getString(1).equals(p)){
//一定合法，用户存在
b=true;
}
}
}catch(Exception e){
e.printStackTrace();
System.out.println("运行检查出错");
}finally{
//关闭打开的各种资源，这个非常重要
this.close();