能显示出一些页面，只是一用到数据库就报错：例如用户时登录界面能正确显示，可是登录时报错。错误如下
type Exception report

message

description The server encountered an internal error that prevented it from fulfilling this request.

exception

java.lang.NullPointerException
    com.wy.tool.JDBConnection.executeQuery(JDBConnection.java:52)
    com.wy.dao.ConsumerDao.getConsumerForm(ConsumerDao.java:98)
    com.wy.webiter.ConsumerServlet.checkConsumer(ConsumerServlet.java:169)
    com.wy.webiter.ConsumerServlet.doGet(ConsumerServlet.java:16)
    com.wy.webiter.ConsumerServlet.doPost(ConsumerServlet.java:186)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:717)


note The full stack trace of the root cause is available in the Apache Tomcat/6.0.36 logs.

请高手指点，本人初学，先谢谢高手们。。。

java.lang.NullPointerException //空指针异常
 com.wy.tool.JDBConnection.executeQuery//有可能是SQL语句错误 ，或者数据库连接错误
com.wy.dao.ConsumerDao.getConsumerForm(ConsumerDao.java:98) //ConsumerDao 98行有错误