Problem with a method in my EJB

[Johan Svensson]

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?

package beans;

import java.util.ArrayList;
import java.util.ListIterator;
import javax.enterprise.context.ApplicationScoped;
import javax.faces.bean.ManagedBean;


/**
 *
 * @author Johan
 */
@ManagedBean
@ApplicationScoped

public class chatHandler {

    String input;
    String userName;
    String currentRoom;

    ArrayList roomList = new ArrayList();
    ListIterator li = roomList.listIterator();

    
    public void addRoom(chatRoom room){
        roomList.add(room);
    }

    public ArrayList getRoomList() {
        return roomList;
    }

    public void setRoomList(ArrayList roomList) {
        this.roomList = roomList;
    }

    public ListIterator getLi() {
        return li;
    }

    public void setLi(ListIterator li) {
        this.li = li;
    }


    public String getCurrentRoom() {    
        return currentRoom;
    }

    public void setCurrentRoom(String currentRoom) {     //<-----This is the method I'm having problems with

        if(!roomList.isEmpty()){    
            while(li.hasNext()){   
                chatRoom cr = ((chatRoom)li.next());
                if(cr.roomName.equalsIgnoreCase(currentRoom)){  
                    cr.setInput(getUserName()+": "+ getInput());             //the class chatRoom also has a method called setInput which adds text to a chat text list.
                    System.out.println("room found, send message here");
                }
                else{                                           
                    roomList.add(new chatRoom(currentRoom));    
                    setCurrentRoom(currentRoom);                
                    System.out.println("no room with that name, but added a new one!");
                }

            }
        }
        else{                       
            roomList.add(new chatRoom(currentRoom));            
            setCurrentRoom(currentRoom);                        
            System.out.println("wrong room");  
        }
        
        
       
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getInput() {
        return input;
    }

    public void setInput(String input) {
        this.input = input;
    }

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

Best Regards

Johan

[Tom Reilly]

I would be suspicious of this:

setCurrentRoom(currentRoom);

which is in two places in the setCurrentRoom() method. That looks recursive to me.

[Dhiraj Mahapatro]

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

....................
  
    public void setCurrentRoom(String currentRoom) {     //<-----This is the method I'm having problems with  
  
        //if(!roomList.isEmpty()){      //Got a handle to the roomList as ListIterator. Now use it....
          if(!li.isEmpty()){
            while(li.hasNext()){     
                chatRoom cr = ((chatRoom)li.next());  
                if(cr.roomName.equalsIgnoreCase(currentRoom)){    
                    cr.setInput(getUserName()+": "+ getInput());             //the class chatRoom also has a method called setInput which adds text to a chat text list.  
                    System.out.println("room found, send message here");  
                }  
                else{                                             
                    //roomList.add(new chatRoom(currentRoom));      //Replace it with li.add(new .......)
                    //setCurrentRoom(currentRoom);                  
                    System.out.println("no room with that name, but added a new one!");  
                }  
  
            }  
        }  
        else{                         
            //roomList.add(new chatRoom(currentRoom));             //Replace it with li.add(new .......)
            //setCurrentRoom(currentRoom);                          
            System.out.println("wrong room");    
        }  
          
   ..........

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

Thanks.....

[Johan Svensson]

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:

    public void setCurrentRoom(String currentRoom) {
        
        if(!roomList.isEmpty()){    

            for(ListIterator li = roomList.listIterator(); li.hasNext();){   
                chatRoom cr = ((chatRoom)li.next());    

                if(cr.roomName.equalsIgnoreCase(currentRoom)){  
                    cr.setInput(getUserName()+": "+ getInput());
                    System.out.println("room found, sending message here.");
                    exists = true; 
                    break;
                    }

                }
            
            if(exists==false){  
                roomList.add(new chatRoom(currentRoom)); 
                setCurrentRoom(currentRoom);   
                System.out.println("Room did not exist, but is now created.");
                }
        }
        
        else{                       
            roomList.add(new chatRoom(currentRoom));            
            setCurrentRoom(currentRoom);                        
            System.out.println("wrong room!!!!");
        }
        exists = false;
        input = "";
        this.currentRoom = currentRoom;
    }

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

[amit punekar]

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]

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]

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