java.util.ConcurrentModificationException while adding elements?

Question

I have a servlet which uses a service to parse a YAML file. but when I put some user traffic on my servlet I get:

SEVERE: Servlet.service() for servlet [SitesController] in context with path [] threw exception [java.util.ConcurrentModificationException] with root cause
java.util.ConcurrentModificationException
    at java.util.ArrayList$SubList.checkForComodification(ArrayList.java:1129)
    at java.util.ArrayList$SubList.listIterator(ArrayList.java:1009)
    ...
    at com.example.UrlRedirectEngin.redirectoToRespectiveSubDomain(UrlRedirectEngin.java:250)

I am not sure if the exception is from parsing the YAML file or not. However the exception is pointing to the line below which I render the page line 250:

request.getRequestDispatcher(JSP_PAGE).forward(request, response);

I just want to know if ConcurrentModificationException can also happens while adding elements to a Map? If yes how can I handle this issue. Thanks.

@tokhi Ican only see lines from within the ArrayList class. In your code, there is only one ArralyList visible. That list is not modified by your code and cannot throw this exception. I yould need the linenumber of YOUR code (and the code) — Christian Kuetbach, May 06 '14 at 19:09
If you down vote the question please also write the reason. thanks. — tokhi, May 06 '14 at 19:15
@ChristianKuetbach: this line: `request.getRequestDispatcher(JSP_PAGE).forward(request, response);` — tokhi, May 06 '14 at 19:18
I think you are missing some important parts in your question: http://stackoverflow.com/questions/3988788/what-is-a-stack-trace-and-how-can-i-use-it-to-debug-my-application-errors — Christian Kuetbach, May 06 '14 at 19:20
let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/52132/discussion-between-christian-kuetbach-and-tokhi) — Christian Kuetbach, May 06 '14 at 19:20

score 1 · Accepted Answer · answered May 06 '14 at 19:56

1

The line

request.getRequestDispatcher(JSP_PAGE).forward(request, response);

forwards to an JSP page. The error may be inside of that JSP as well (the part of the stacktrace may hide the original error)

answered May 06 '14 at 19:56

Christian Kuetbach

15,850
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score 0 · Answer 2 · answered May 06 '14 at 19:23

0

ConcurrentModificationException means that you are editing your map/collection when you try to read it. Simple example :

final List<String> list = new ArrayList<String>()
    private static final long serialVersionUID = 1L; {
        {
            add("Hi");
            add("This is a test");
        }
    };
for(final String string : list) {
    if(string.equals("Hi")) {
        list.remove("Hi");
    }
}

I think getRequestDispatcher is modifying your map while your using it.

answered May 06 '14 at 19:23

Skyost

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but I'm not removing anything – tokhi May 06 '14 at 19:28
But maybe you are changing some things. – Skyost May 06 '14 at 19:41

java.util.ConcurrentModificationException while adding elements?

2 Answers2