HTTP Status 500 - java.lang.NullPointerException

Question

HTTP Status 500 - java.lang.NullPointerException

type Exception report

message java.lang.NullPointerException

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

exception org.apache.jasper.JasperException: java.lang.NullPointerException
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:549)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

root cause java.lang.NullPointerException
org.easybooks.bookstore.jdbc.MySQLConnBean.executeQuery(MySQLConnBean.java:30)
org.apache.jsp.validate_jsp._jspService(validate_jsp.java:85)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

note The full stack trace of the root cause is available in the
Apache Tomcat/7.0.30 logs.

【这是什么问题？】

Answer 1

错误描述：空指针异常；
错误原因：调用了未被初始化对象的方法导致；
处理办法：根据错误提示，检查一下你的MySQLConnBean类的第30行。追问

stmt = conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_UPDATABLE);

30行是这个

追答

conn 这个应该是null，你可以在调用前打印出来看一下。

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