Question

在调试动态网页时出现http500错误怎么办？

HTTP Status 500-
type Exception report
description The server encountered an internal error () that prevented it from fulfilling this request.
exception

javax.servlet.ServletException: java.lang.NullPointerException
org.apache.struts.action.RequestProcessor.processException(RequestProcessor.java:535)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:433)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

root cause

java.lang.NullPointerException
com.tools.ConnDB.executeQuery(ConnDB.java:59)
com.dao.SongDAO.queryType(SongDAO.java:19)
com.action.SongAction.main(SongAction.java:68)
com.action.SongAction.execute(SongAction.java:34)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)

note The full stack trace of the root cause is available in the Apache Tomcat/6.0.10 logs.

Answer 1

http 500表示服务器内部错误
可能的原因是，在服务器端发生的异常，例如你的代码有问题无法完成请求的处理，Web服务器配置有误，或者数据库连接不上，导致在前端浏览器上无法正常根据请求来响应，就会报500错误
看到了吗，你发生的这个错误是：
java.lang.NullPointerException
可能是获取到的数据库连接（Connection）为null，调试跟踪，检查一下吧

Answer 2

数据库连接错误
没有获取到相应的东西，NullPointerException---空指针异常

Answer 3

数据库连接有问题