Re: Tomcat Server - Arraylist java.util.ConcurrentModificationException issue

[Terence M. Bandoian]

On 2/2/2016 3:54 AM, Subhro Paul wrote:

From:   "Terence M. Bandoian" 
To: Tomcat Users List 
Date:   02/01/2016 07:58 PM
Subject:Tomcat Server - Arraylist
java.util.ConcurrentModificationException issue



On 2/1/2016 6:50 AM, Subhro Paul wrote:

Hi Team,

Our web application has a "header.jsp" which has 2  Arraylist on it.

Each

ArrayList has more than 50 items inside. The code is to identify the
mobile device and requested page and transfer the call to mobile page
accordingly.

This code works fine once we restart the server and can continue running

2

months without any issue. But day by day it starts showing 500 error

with

exception in log "ConcurrentModificationException". Below is the code
snippet of JSP code. My Question is why this issue is happening around 2
months? If we clear the temp file created by the server in work folder
then that will run for some time( 2- 3 days) and then again the same
exception starts occurring. I have identified one solution by moving the
JAVA code from JSP to JAVA file which worked good while perform testing
but client wants to know the root cause of the issue.

FYI, earlier we had Vector in place of Arraylist which gave trouble of
thread blocking due to synchronization. So, converting from Arraylist to
Vector will not be a good idea.


Exception:

java.util.ConcurrentModificationException
  at
java.util.ArrayList$Itr.checkForComodification(ArrayList.java:859)
  at java.util.ArrayList$Itr.next(ArrayList.java:831)
  at
org.apache.jsp.includes.header_jsp.isHomePage(header_jsp.java:97)


Code Snippet:

<%!
private Set uas = new HashSet();
ArrayList urlnames = new ArrayList();
ArrayList excludePathList = new ArrayList();


Hi, Subhro-

Fields declared in a declarations section (<%!  ... %>) are class



That should be "instance" variables.


  
variables.  If Tomcat uses a single JSP object to serve multiple

requests, which I believe it does, access to these fields should be made
thread safe.  A simple solution would be to move the declarations of
these fields to a scriptlet section (<% ... %>) which would result in
them being local to the JSP service method.  It isn't the most efficient
way to go about it but it should solve the concurrent access problem
you're seeing.

-Terence Bandoian
/http://www.tmbsw.com/
/


private boolean haveToRedirect(HttpServletRequest request,
  String stopMobiCookie) {
  boolean doRedirect = false;

  String userAgent = request.getHeader("User-Agent");
  if (! stopMobiCookie.equals("yes") && userAgent != null &&
userAgent.length()!=0 && (userAgent.indexOf("UsableNet")==-1))
  {

  Iterator iter = uas.iterator();
  while (iter.hasNext()) {
  if (userAgent.indexOf((String)iter.next())!=-1)

{

  doRedirect = true;
  break;


  }
  }
  }
  return doRedirect;
}

  private boolean isHomePage(HttpServletRequest request){
  Iterator itr = urlnames.iterator();
  String path = "";
  while (itr.hasNext()) {
   path = itr.next();
   if
(request.getRequestURI().toString().equalsIgnoreCase(path)){
   return true;
   }
  }
  return false;
  }

  private boolean isExcludePath(HttpServletRequest request){
  Iterator itr = excludePathList.iterator();
  String path = "";
  while (itr.hasNext()) {
   path = itr.next();
   if (request.getRequestURI().startsWith(path)

&&

!request.getRequestURI().startsWith("/info/contact.jsp")){
   return true;
   }
  }
  return false;
  }

%>


<%

uas.add("Blazer");
uas.add("Danger hiptop");
uas.add("DoCoMo/");
uas.add("Ericsson");
uas.add("Googlebot-Mobile");
uas.add("MSN Mobile Proxy");
uas.add("Handheld");
uas.add("HTC_HD2_T58585 Opera");
uas.add("iPhone");
uas.add("iPod");
uas.add("Klondike");
uas.add("LG-");
uas.add("LGE-");
... Arround 40 items


excludePathList.add("/business/my_account");
excludePathList.add("/business/save_energy");
excludePathList.add("/business/services");
excludePathList.add("/business/small_large_business");
excludePathList.add("/info/environment");
excludePathList.add("/info/about");
excludePathList.add("/info/index.jsp");
excludePathList.add("/info/ambassador.jsp");
 more than 50 items


stopMobiCookie = some cookie code

boolean doRedirect = haveToRedirect((HttpServletRequest)request,
stopMobiCookie);


if(doRedirect){
  boolean isHomePage =

Re: Tomcat Server - Arraylist java.util.ConcurrentModificationException issue

[Subhro Paul]

From:   "Terence M. Bandoian" 
To: Tomcat Users List 
Date:   02/01/2016 07:58 PM
Subject:Tomcat Server - Arraylist 
java.util.ConcurrentModificationException issue



On 2/1/2016 6:50 AM, Subhro Paul wrote:
> Hi Team,
>
> Our web application has a "header.jsp" which has 2  Arraylist on it. 
Each
> ArrayList has more than 50 items inside. The code is to identify the
> mobile device and requested page and transfer the call to mobile page
> accordingly.
>
> This code works fine once we restart the server and can continue running 
2
> months without any issue. But day by day it starts showing 500 error 
with
> exception in log "ConcurrentModificationException". Below is the code
> snippet of JSP code. My Question is why this issue is happening around 2
> months? If we clear the temp file created by the server in work folder
> then that will run for some time( 2- 3 days) and then again the same
> exception starts occurring. I have identified one solution by moving the
> JAVA code from JSP to JAVA file which worked good while perform testing
> but client wants to know the root cause of the issue.
>
> FYI, earlier we had Vector in place of Arraylist which gave trouble of
> thread blocking due to synchronization. So, converting from Arraylist to
> Vector will not be a good idea.
>
>
> Exception:
>
> java.util.ConcurrentModificationException
>  at
> java.util.ArrayList$Itr.checkForComodification(ArrayList.java:859)
>  at java.util.ArrayList$Itr.next(ArrayList.java:831)
>  at
> org.apache.jsp.includes.header_jsp.isHomePage(header_jsp.java:97)
>
>
> Code Snippet:
>
> <%!
> private Set uas = new HashSet();
> ArrayList urlnames = new ArrayList();
> ArrayList excludePathList = new ArrayList();


Hi, Subhro-

Fields declared in a declarations section (<%!  ... %>) are class 
variables.  If Tomcat uses a single JSP object to serve multiple 
requests, which I believe it does, access to these fields should be made 
thread safe.  A simple solution would be to move the declarations of 
these fields to a scriptlet section (<% ... %>) which would result in 
them being local to the JSP service method.  It isn't the most efficient 
way to go about it but it should solve the concurrent access problem 
you're seeing.

-Terence Bandoian
/http://www.tmbsw.com/
/

>
> private boolean haveToRedirect(HttpServletRequest request,
>  String stopMobiCookie) {
>  boolean doRedirect = false;
> 
>  String userAgent = request.getHeader("User-Agent");
>  if (! stopMobiCookie.equals("yes") && userAgent != null &&
> userAgent.length()!=0 && (userAgent.indexOf("UsableNet")==-1))
>  {
>
>  Iterator iter = uas.iterator();
>  while (iter.hasNext()) {
>  if (userAgent.indexOf((String)iter.next())!=-1) 
{
>  doRedirect = true;
>  break;
>
>
>  }
>  }
>  }
>  return doRedirect;
> }
>
>  private boolean isHomePage(HttpServletRequest request){
>  Iterator itr = urlnames.iterator();
>  String path = "";
>  while (itr.hasNext()) {
>   path = itr.next();
>   if
> (request.getRequestURI().toString().equalsIgnoreCase(path)){
>   return true;
>   }
>  }
>  return false;
>  }
> 
>  private boolean isExcludePath(HttpServletRequest request){
>  Iterator itr = excludePathList.iterator();
>  String path = "";
>  while (itr.hasNext()) {
>   path = itr.next();
>   if (request.getRequestURI().startsWith(path) 
&&
> !request.getRequestURI().startsWith("/info/contact.jsp")){
>   return true;
>   }
>  }
>  return false;
>  }
>
> %>
>
>
> <%
>
> uas.add("Blazer");
> uas.add("Danger hiptop");
> uas.add("DoCoMo/");
> uas.add("Ericsson");
> uas.add("Googlebot-Mobile");
> uas.add("MSN Mobile Proxy");
> uas.add("Handheld");
> uas.add("HTC_HD2_T58585 Opera");
> uas.add("iPhone");
> uas.add("iPod");
> uas.add("Klondike");
> uas.add("LG-");
> uas.add("LGE-");
> ... Arround 40 items
>
>
> excludePathList.add("/business/my_account");
> excludePathList.add("/business/save_energy");
> excludePathList.add("/business/services");
> excludePathList.add("/business/small_large_business");
> excludePathList.add("/info/environment");
> excludePathList.add("/info/about");
> excludePathList.add("/info/index.jsp");
> excludePathList.add("/info/ambassador.jsp");
>  more than 50 items
>
>
> stopMobiCookie = some cookie code
>
> boolean doRedirect = haveToRedirect((HttpServletRequest)request,
> 

Re: Tomcat Server - Arraylist java.util.ConcurrentModificationException issue

[Christopher Schultz]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA1

Paul,

Please don't hijack threads. If you want to start a new thread, please
start a new email message addressed to this list; don't find an
existing message and reply to it.

- -chris

On 2/1/16 7:50 AM, Subhro Paul wrote:
> Hi Team,
> 
> Our web application has a "header.jsp" which has 2  Arraylist on
> it. Each ArrayList has more than 50 items inside. The code is to
> identify the mobile device and requested page and transfer the call
> to mobile page accordingly.
> 
> This code works fine once we restart the server and can continue
> running 2 months without any issue. But day by day it starts
> showing 500 error with exception in log
> "ConcurrentModificationException". Below is the code snippet of JSP
> code. My Question is why this issue is happening around 2 months?
> If we clear the temp file created by the server in work folder then
> that will run for some time( 2- 3 days) and then again the same 
> exception starts occurring. I have identified one solution by
> moving the JAVA code from JSP to JAVA file which worked good while
> perform testing but client wants to know the root cause of the
> issue.
> 
> FYI, earlier we had Vector in place of Arraylist which gave trouble
> of thread blocking due to synchronization. So, converting from
> Arraylist to Vector will not be a good idea.
> 
> 
> Exception:
> 
> java.util.ConcurrentModificationException at 
> java.util.ArrayList$Itr.checkForComodification(ArrayList.java:859) 
> at java.util.ArrayList$Itr.next(ArrayList.java:831) at 
> org.apache.jsp.includes.header_jsp.isHomePage(header_jsp.java:97)
> 
> 
> Code Snippet:
> 
> <%! private Set uas = new HashSet(); ArrayList urlnames =
> new ArrayList(); ArrayList excludePathList = new
> ArrayList();
> 
> private boolean haveToRedirect(HttpServletRequest request, String
> stopMobiCookie) { boolean doRedirect = false;
> 
> String userAgent = request.getHeader("User-Agent"); if (!
> stopMobiCookie.equals("yes") && userAgent != null && 
> userAgent.length()!=0 && (userAgent.indexOf("UsableNet")==-1)) {
> 
> Iterator iter = uas.iterator(); while (iter.hasNext()) { if
> (userAgent.indexOf((String)iter.next())!=-1) { doRedirect = true; 
> break;
> 
> 
> } } } return doRedirect; }
> 
> private boolean isHomePage(HttpServletRequest request){ 
> Iterator itr = urlnames.iterator(); String path = ""; while
> (itr.hasNext()) { path = itr.next(); if 
> (request.getRequestURI().toString().equalsIgnoreCase(path)){ return
> true; } } return false; }
> 
> private boolean isExcludePath(HttpServletRequest request){ 
> Iterator itr = excludePathList.iterator(); String path =
> ""; while (itr.hasNext()) { path = itr.next(); if
> (request.getRequestURI().startsWith(path) && 
> !request.getRequestURI().startsWith("/info/contact.jsp")){ return
> true; } } return false; }
> 
> %>
> 
> 
> <%
> 
> uas.add("Blazer"); uas.add("Danger hiptop"); uas.add("DoCoMo/"); 
> uas.add("Ericsson"); uas.add("Googlebot-Mobile"); uas.add("MSN
> Mobile Proxy"); uas.add("Handheld"); uas.add("HTC_HD2_T58585
> Opera"); uas.add("iPhone"); uas.add("iPod"); uas.add("Klondike"); 
> uas.add("LG-"); uas.add("LGE-"); ... Arround 40 items
> 
> 
> excludePathList.add("/business/my_account"); 
> excludePathList.add("/business/save_energy"); 
> excludePathList.add("/business/services"); 
> excludePathList.add("/business/small_large_business"); 
> excludePathList.add("/info/environment"); 
> excludePathList.add("/info/about"); 
> excludePathList.add("/info/index.jsp"); 
> excludePathList.add("/info/ambassador.jsp");  more than 50
> items
> 
> 
> stopMobiCookie = some cookie code
> 
> boolean doRedirect = haveToRedirect((HttpServletRequest)request, 
> stopMobiCookie);
> 
> 
> if(doRedirect){ boolean isHomePage = 
> isHomePage((HttpServletRequest)request); boolean isExcludePath = 
> isExcludePath((HttpServletRequest)request);
> 
> session.setAttribute("mobile_agent", "yes");
> 
> if(!isHomePage && !isExcludePath){ String mobileServer =
> "mobile.server.com"; try{ mobileServer = mobileServer + 
> request.getRequestURI().toString(); }catch(Exception e){} %> 
>  window.location 
> ="<%=mobileServer%>";  <% } } %>
> 
> 
> 
> Thanks & Regards Subhro Paul =-=-= Notice: The
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