Why did Servlet service for servlet jsp throw this exception

Question

I get the following error  what could be the problem   My context descriptor    lt  xml version  1 0  encoding  UTF-8   gt   lt web-app xmlns xsi  http   www w3 org 2001 XMLSchema-instance  xmlns  http   java sun com xml ns javaee  xmlns web  http   java sun com xml ns javaee web-app 2 5 xsd  xsi schemaLocation  http   java sun com xml ns javaee http   java sun com xml ns javaee web-app 2 5 xsd  id  WebApp ID  version  2 5  gt      lt servlet gt       lt servlet-name gt UploadServlet lt  servlet-name gt       lt servlet-class gt controller UploadServlet lt  servlet-class gt     lt  servlet gt      lt servlet-mapping gt       lt servlet-name gt UploadServlet lt  servlet-name gt       lt url-pattern gt  UploadServlet lt  url-pattern gt     lt  servlet-mapping gt     lt welcome-file-list gt       lt welcome-file gt index jsp lt  welcome-file gt     lt  welcome-file-list gt   lt  web-app gt      SEVERE  Servlet service   for servlet jsp threw exception java lang NullPointerException     at org apache jsp index jsp  jspInit index jsp java 22      at org apache jasper runtime HttpJspBase init HttpJspBase java 52      at org apache jasper servlet JspServletWrapper getServlet JspServletWrapper java 159      at org apache jasper servlet JspServletWrapper service JspServletWrapper java 329      at org apache jasper servlet JspServlet serviceJspFile JspServlet java 342      at org apache jasper servlet JspServlet service JspServlet java 267      at javax servlet http HttpServlet service HttpServlet java 717      at org apache catalina core ApplicationFilterChain internalDoFilter ApplicationFilterChain java 290      at org apache catalina core ApplicationFilterChain doFilter ApplicationFilterChain java 206      at org apache catalina core StandardWrapperValve invoke StandardWrapperValve java 233      at org apache catalina core StandardContextValve invoke StandardContextValve java 191      at org apache catalina core StandardHostValve invoke StandardHostValve java 128      at org apache catalina valves ErrorReportValve invoke ErrorReportValve java 102      at org apache catalina core StandardEngineValve invoke StandardEngineValve java 109      at org apache catalina connector CoyoteAdapter service CoyoteAdapter java 293      at org apache coyote http11 Http11Processor process Http11Processor java 849      at org apache coyote http11 Http11Protocol Http11ConnectionHandler process Http11Protocol java 583      at org apache tomcat util net JIoEndpoint Worker run JIoEndpoint java 454      at java lang Thread run Unknown Source  Feb 23  2010 11 35 28 PM org apache catalina core StandardWrapperValve invoke SEVERE  Servlet service   for servlet jsp threw exception java lang NullPointerException     at org apache jsp index jsp  jspInit index jsp java 22      at org apache jasper runtime HttpJspBase init HttpJspBase java 52      at org apache jasper servlet JspServletWrapper getServlet JspServletWrapper java 159      at org apache jasper servlet JspServletWrapper service JspServletWrapper java 329      at org apache jasper servlet JspServlet serviceJspFile JspServlet java 342      at org apache jasper servlet JspServlet service JspServlet java 267      at javax servlet http HttpServlet service HttpServlet java 717      at org apache catalina core ApplicationFilterChain internalDoFilter ApplicationFilterChain java 290      at org apache catalina core ApplicationFilterChain doFilter ApplicationFilterChain java 206      at org apache catalina core StandardWrapperValve invoke StandardWrapperValve java 233      at org apache catalina core StandardContextValve invoke StandardContextValve java 191      at org apache catalina core StandardHostValve invoke StandardHostValve java 128      at org apache catalina valves ErrorReportValve invoke ErrorReportValve java 102      at org apache catalina core StandardEngineValve invoke StandardEngineValve java 109      at org apache catalina connector CoyoteAdapter service CoyoteAdapter java 293      at org apache coyote http11 Http11Processor process Http11Processor java 849      at org apache coyote http11 Http11Protocol Http11ConnectionHandler process Http11Protocol java 583      at org apache tomcat util net JIoEndpoint Worker run JIoEndpoint java 454      at java lang Thread run Unknown Source

User · Accepted Answer

It can be caused by a classpath contamination  Check that you  WEB-INF lib doesn t contain something like jsp-api-  jar

User · Answer

I had this error  it happened somewhat spontaneously  and the page would halt in the browser in the middle of an HTML tag  not a section of code   It was baffling   Turns out  I let a variable go out of scope and the garbage collector swept it away and then I tried to use it  Thus the seemingly-random timing   To give a more concrete example    Inside a method  I had something like   Foo   foos   new Foo 20      fill up the  foos  array    return Arrays asList foos      this returns type List lt Foo gt    Now in my JSP page  I called that method and used the List object returned by it  The List object is backed by that  foos  array  but  the array went out of scope when I returned from the method  since it is a local variable   So shortly after returning  the garbage collector swept away the  foos  array  and my access to the List caused a NullPointerException since its underlying array was now wiped away   I actually wondered  as I wrote the above method  whether that would happen   The even deeper underlying problem was premature optimization  I wanted a list  but I knew I would have exactly 20 elements  so I figured I d try to be more efficient than new ArrayList lt Foo gt  20  which only sets an initial size of 20 but can possibly be less efficient than the method I used  So of course  to fix it  I just created my ArrayList  filled it up  and returned it  No more strange error

User · Answer

If your project is Maven-based  remember to set scope to provided for such dependencies as servlet-api  jsp-api  Otherwise  these jars will be exported to WEB-INF lib and hence contaminate with those in Tomcat server  That causes painful problems    lt dependency gt     lt groupId gt javax servlet lt  groupId gt     lt artifactId gt servlet-api lt  artifactId gt     lt version gt 2 5 lt  version gt     lt scope gt provided lt  scope gt   lt  dependency gt   lt dependency gt     lt groupId gt javax servlet jsp lt  groupId gt     lt artifactId gt jsp-api lt  artifactId gt     lt version gt 2 1 lt  version gt     lt scope gt provided lt  scope gt   lt  dependency gt

User · Answer

The problem is in your JSP  most likely you are calling a method on an object that is null at runtime   It is happening in the  jspInit   call  which is a little more unusual    the problem code is probably a method declaration like  lt      gt     Update  I ve only reproduced this by overriding the  jspInit   method  Is that what you re doing  If so  it s not recommended - that s why it starts with an

User · Answer

I tried my best to follow the answers given above. But I have below reason for the same.

Note: This is for maven+eclipse+tomcat deployment and issue faced especially with spring mvc.

1- If you are including servlet and jsp dependency please mark them provided in scope.

<dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>3.1.0</version>
        <scope>provided</scope>
    </dependency>
    <dependency>
        <groupId>javax.servlet.jsp</groupId>
        <artifactId>javax.servlet.jsp-api</artifactId>
        <version>2.3.1</version>
        <scope>provided</scope>
    </dependency>

Possibly you might be including jstl as dependency. So, jsp-api.jar and servlet-api.jar will be included along. So, require to exclude the servlet-api and jsp-api being deployed as required lib in target or in "WEB-INF/lib" as given below.

<dependency>
    <groupId>javax.servlet.jsp.jstl</groupId>
    <artifactId>jstl-api</artifactId>
    <version>1.2</version>
    <exclusions>
        <exclusion>
            <artifactId>servlet-api</artifactId>
            <groupId>javax.servlet</groupId>
        </exclusion>
        <exclusion>
            <artifactId>jsp-api</artifactId>
            <groupId>javax.servlet.jsp</groupId>
        </exclusion>
    </exclusions>
</dependency>

[java] Why did Servlet.service() for servlet jsp throw this exception?

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