HTTP Status 500 - Error instantiating servlet class pkg coreServlet

Question

I am creating simple servlet and deploying it in tomcat server but I am getting the following error      HTTP Status 500 - Error instantiating servlet class pkg coreServlet   File Structure on the tomcat server   webapps         - aarya       - WEB-INF            -web xml      -src folder                  -pkg                     -coreServlet class   web xml    lt  xml version  1 0  encoding  UTF-8   gt   lt web-app version  2 4  xmlns  http   java sun com xml ns j2ee      xmlns xsi  http   www w3 org 2001 XMLSchema-instance      xsi schemaLocation  http   java sun com xml ns j2ee      http   java sun com xml ns j2ee web-app 2 4 xsd  gt     lt servlet gt       lt servlet-name gt aaryaservlet lt  servlet-name gt       lt servlet-class gt pkg coreServlet lt  servlet-class gt   lt  servlet gt    lt servlet-mapping gt       lt servlet-name gt aaryaservlet lt  servlet-name gt           lt url-pattern gt  coreServlet lt  url-pattern gt       lt  servlet-mapping gt   lt  web-app gt    coreServlet java   package pkg   import java io    import javax servlet    import javax servlet http      public class coreServlet extends HttpServlet                               private static final long serialVersionUID   1L   public void doGet HttpServletRequest req HttpServletResponse res   throws ServletException IOException                PrintWriter out   res getWriter            res setContentType  text html            out println  this is First servlet Example               url I am giving is http   localhost 8080 aarya coreServlet I try by restarting tomcat but I am getting same error  Where I am doing wrong

User · Answer

Make sure the following    Proper  war  file structure i e  WEB-INF  amp  META-INF  web xml  file is setup correct  Last and important  private static final long serialVersionUID   1L  should be there in your class   lt servlet-class gt MyClass lt  servlet-class gt

User · Answer

Change the  private static final long serialVersionUID   1L    to any other value like   private static final long serialVersionUID   102831973239L    also you can generate it automatically in eclipse   It is because each servlet in a app has a unique id and tomcat causes problem with two servlets having same id

User · Answer

I had an issue with Servlet instantiation  I cleaned the project and it worked for me  In eclipse menu  Go to Project- Clean  It should work

User · Answer

The servlet class should be in the WEB-INF classes not WEB-INF src

User · Answer

The above error can occur for multiple cases during servlet startup   request  Hope you check the full stack trace of the server log  If you have tomcat  you can also see the exact causes  in html preview of the 500 Internal Server Error page    Weird thing is  if you try to hit the request url a second time  you would get 404 Not Found page   You can also debug this issue  by placing breakpoints on all the classes constructor initialization block  whose objects are created during servlet startup request   In my case  I didn t had javaassist jar loaded for the Weld CDI injection to work  And it shown NoClassDefFound Error

User · Answer

In my case missing private static final long serialVersionUID   1L  line caused the same error  I added the line and it worked

User · Answer

Do not put the src folder in the WEB-INF directory

User · Answer

Try This     before -   lt servlet gt       lt servlet-name gt TestServlet lt  servlet-name gt       lt servlet-class gt TestServlet lt  servlet-class gt     lt  servlet gt    After -    lt servlet gt       lt servlet-name gt TestServlet lt  servlet-name gt       lt servlet-class gt operation TestServlet lt  servlet-class gt    lt  servlet gt

User · Answer

Have you closed the  lt  web-app   tag in your web xml  From what you have posted  the closing tag seems to be missing

[java] HTTP Status 500 - Error instantiating servlet class pkg.coreServlet

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