Now in the java background, as long as you modify a little bit of code, the previous page will report 500, and you have to log in again? - Codes Helper - Programming Question Answer

Now in the java background, as long as you modify a little bit of code, the previous page will report 500, and you have to log in again?

even if you add a line of comments, the previous paragraph will report a 500 error as soon as it is refreshed. You must log in to the system again. Was it all right in the past?

message 

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

exception 

org.apache.jasper.JasperException
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:372)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:802)


root cause 

java.lang.NullPointerException
    org.apache.jsp.trade.home.qdmenu.menu001_jsp._jspService(menu001_jsp.java:324)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:802)


note The full stack trace of the root cause is available in the Apache Tomcat/5.0.28 logs.

Apr.03,2021

this is reported a null pointer, for your so-called re-login situation, the high probability is that the page needs authentication and other operations, considering that most of these operations rely on session or model to do, so you need to check whether the null pointer on your page caused by the use of such parameters, variables.

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