Help coderanch get a
new server
by contributing to the fundraiser
  • Post Reply Bookmark Topic Watch Topic
  • New Topic
programming forums Java Mobile Certification Databases Caching Books Engineering Micro Controllers OS Languages Paradigms IDEs Build Tools Frameworks Application Servers Open Source This Site Careers Other Pie Elite all forums
this forum made possible by our volunteer staff, including ...
Marshals:
  • Campbell Ritchie
  • Jeanne Boyarsky
  • Ron McLeod
  • Paul Clapham
  • Liutauras Vilda
Sheriffs:
  • paul wheaton
  • Rob Spoor
  • Devaka Cooray
Saloon Keepers:
  • Stephan van Hulst
  • Tim Holloway
  • Carey Brown
  • Frits Walraven
  • Tim Moores
Bartenders:
  • Mikalai Zaikin

Problem with a method in my EJB

 
Greenhorn
Posts: 4
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Hi!
I'm rather new to J2EE and I am right now trying to develop a chat application for a school project. I'm having problems with one of the methods in my bean and I was wondering if someone here might be able to help me (setCurrentRoom(String currentRoom) in the following code). I get a "java.util.ConcurrentModificationException" -exception when I try to set the string currentRoom to a certain value from my jsp. The class chatRoom is defined in another application scoped bean. Does anyone know what the problem might be?



Been stuck on this project for a long time now, would really appreciate some help!

Best Regards

Johan

 
Rancher
Posts: 618
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
I would be suspicious of this:

which is in two places in the setCurrentRoom() method. That looks recursive to me.
 
Greenhorn
Posts: 12
Eclipse IDE Spring Tomcat Server
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
I guess Tom is correct.
In addition to that I would suggest to use the ListIterator li wherever possible in place of directly handling the ArrayList in the code.

The basic theory beneath this is "You have your guy [iterator] to do the work for a Customer[arraylist]. you need not contact the customer[arraylist] directly. Route through the guy [iterator]"
If anyone tries to handle both the jobs, you develop a concurrency and hence java.util.ConcurrentModificationException.

The code would look like




Try this way. It should work. Please also look at the recursion.

Thanks.....
 
Johan Svensson
Greenhorn
Posts: 4
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Hey guys!

I finally figured it out, thank you so much for the help! apparently ListIterator() does not have a method called isEmpty though, so I still used the ArrayList itself. Anyway I honestly don't know exactly what was wrong, since it worked when I used a for-loop instead of the while-loop. I did however add a global boolean variable called exists to keep track of when to exit the for-loop and when to enter the following if-statement. I'm still using the recursion, since I think its kinda neat Here is the working code:



Anyway thanks for the help! I will definitely continue using this forum when it comes to Java programming, its been a very positive experience so far


Best Regards

Johan
 
Ranch Hand
Posts: 544
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Hello there,
Looking at your code in setCurrentRoom() I think you should consider using a Map (Key - Room name and Value - ChatRoom object). This will highly simplify your logic and lines of code needed to do the iteration on arraylist and comparing room names individually.

Regards,
Amit
 
Johan Svensson
Greenhorn
Posts: 4
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
The thing is.. I need to be able to iterate over the list in my JSP site. Wouldn't using a map cause problems with this? I don't wanna use Java script in my JSP, only JSTL.

//Johan
 
amit punekar
Ranch Hand
Posts: 544
  • Mark post as helpful
  • send pies
    Number of slices to send:
    Optional 'thank-you' note:
  • Quote
  • Report post to moderator
Hello,
JSTL can handle the Map iterations as well. Sorry, I do not have any example at the moment that I could have posted here.

Regds,
Amit
 
Look! It's Leonardo da Vinci! And he brought a tiny ad!
We need your help - Coderanch server fundraiser
https://coderanch.com/t/782867/Coderanch-server-fundraiser
reply
    Bookmark Topic Watch Topic
  • New Topic