执行页面出现 HTTP Status 500

Question

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

exception
java.lang.NullPointerException
com.dao.BooksDao.selBookByPage(BooksDao.java:30)
com.servlet.IndexServlet.doPost(IndexServlet.java:70)
com.servlet.IndexServlet.doGet(IndexServlet.java:25)
javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
com.filter.EncodeFilter.doFilter(EncodeFilter.java:24)
note The full stack trace of the root cause is available in the Apache Tomcat/7.0.57 logs.
错误页面出现这个情况，怎么解决呢
求大神们帮助

Answer 1

报500是说服务器出了问题，从你的报错信息来看是产生了空指针异常，也就是一个对象还没有实例化就使用报错信息中给出了两个个文件：BooksDao.java、IndexServlet.java按照给出的代码行数去看是哪个对象没有实例化，把它实例化就好了