title: Getting java heap space issues in Tomcat 7
body: <p>I am working on a Java EE web application, which consists of Struts, Spring and Hibernate. In that, I get the  following exceptions repeatedly (at least once a day). </p>
  
  <p><strong>Exception 1 :</strong></p>
  
  <pre><code>Exception in thread "Timer-0" java.lang.OutOfMemoryError: Java heap space
      at java.util.LinkedHashMap.createEntry(LinkedHashMap.java:424)
      at java.util.LinkedHashMap.addEntry(LinkedHashMap.java:406)
      at java.util.HashMap.put(HashMap.java:385)
      at sun.util.resources.OpenListResourceBundle.loadLookup(OpenListResourceBundle.java:118)
      at sun.util.resources.OpenListResourceBundle.loadLookupTablesIfNecessary(OpenListResourceBundle.java:97)
      at sun.util.resources.OpenListResourceBundle.handleGetObject(OpenListResourceBundle.java:58)
      at sun.util.resources.TimeZoneNamesBundle.handleGetObject(TimeZoneNamesBundle.java:59)
      at java.util.ResourceBundle.getObject(ResourceBundle.java:368)
      at java.util.ResourceBundle.getObject(ResourceBundle.java:371)
      at java.util.ResourceBundle.getStringArray(ResourceBundle.java:351)
      at sun.util.TimeZoneNameUtility.retrieveDisplayNames(TimeZoneNameUtility.java:100)
      at sun.util.TimeZoneNameUtility.retrieveDisplayNames(TimeZoneNameUtility.java:81)
      at java.util.TimeZone.getDisplayNames(TimeZone.java:399)
      at java.util.TimeZone.getDisplayName(TimeZone.java:350)
      at java.text.SimpleDateFormat.subFormat(SimpleDateFormat.java:1110)
      at java.text.SimpleDateFormat.format(SimpleDateFormat.java:899)
      at java.text.SimpleDateFormat.format(SimpleDateFormat.java:869)
      at java.text.DateFormat.format(DateFormat.java:316)
      at org.apache.log4j.helpers.PatternParser$DatePatternConverter.convert(PatternParser.java:443)
      at org.apache.log4j.helpers.PatternConverter.format(PatternConverter.java:65)
      at org.apache.log4j.PatternLayout.format(PatternLayout.java:506)
      at org.apache.log4j.WriterAppender.subAppend(WriterAppender.java:310)
      at org.apache.log4j.DailyRollingFileAppender.subAppend(DailyRollingFileAppender.java:369)
      at org.apache.log4j.WriterAppender.append(WriterAppender.java:162)
      at org.apache.log4j.AppenderSkeleton.doAppend(AppenderSkeleton.java:251)
      at org.apache.log4j.helpers.AppenderAttachableImpl.appendLoopOnAppenders(AppenderAttachableImpl.java:66)
      at org.apache.log4j.Category.callAppenders(Category.java:206)
      at org.apache.log4j.Category.forcedLog(Category.java:391)
      at org.apache.log4j.Category.log(Category.java:856)
      at com.mchange.v2.log.log4j.Log4jMLog$Log4jMLogger.log(Log4jMLog.java:161)
      at com.mchange.v2.log.log4j.Log4jMLog$Log4jMLogger.warning(Log4jMLog.java:221)
      at com.mchange.v2.async.ThreadPoolAsynchronousRunner$DeadlockDetector.run(ThreadPoolAsynchronousRunner.java:624)
  </code></pre>
  
  <p><strong>Exception 2 :</strong></p>
  
  <pre><code>Exception in thread "com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#1" java.lang.OutOfMemoryError: GC overhead limit exceeded
      at java.util.HashMap.addEntry(HashMap.java:753)
      at java.util.HashMap.put(HashMap.java:385)
      at java.util.HashSet.add(HashSet.java:200)
      at com.mchange.v2.c3p0.util.ConnectionEventSupport.addConnectionEventListener(ConnectionEventSupport.java:39)
      at com.mchange.v2.c3p0.impl.NewPooledConnection.addConnectionEventListener(NewPooledConnection.java:237)
      at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.refurbishResourceOnCheckin(C3P0PooledConnectionPool.java:292)
      at com.mchange.v2.resourcepool.BasicResourcePool.attemptRefurbishResourceOnCheckin(BasicResourcePool.java:1606)
      at com.mchange.v2.resourcepool.BasicResourcePool.access$200(BasicResourcePool.java:32)
      at com.mchange.v2.resourcepool.BasicResourcePool$1RefurbishCheckinResourceTask.run(BasicResourcePool.java:1228)
      at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
  Exception in thread "com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#4" java.lang.OutOfMemoryError: GC overhead limit exceeded
  Exception in thread "Task-Thread-for-com.mchange.v2.async.ThreadPerTaskAsynchronousRunner@6c8bb765" java.lang.OutOfMemoryError: GC overhead limit exceeded
  Exception in thread "com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#3" java.lang.OutOfMemoryError: GC overhead limit exceeded
  Exception in thread "com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#2" java.lang.OutOfMemoryError: GC overhead limit exceeded
  Exception in thread "Task-Thread-for-com.mchange.v2.async.ThreadPerTaskAsynchronousRunner@6c8bb765" java.lang.OutOfMemoryError: GC overhead limit exceeded
  Exception in thread "Task-Thread-for-com.mchange.v2.async.ThreadPerTaskAsynchronousRunner@6c8bb765" java.lang.OutOfMemoryError: GC overhead limit exceeded
  Exception in thread "Timer-0" java.lang.OutOfMemoryError: Java heap space
  Exception in thread ""http-bio-8080"-exec-2" java.lang.OutOfMemoryError: Java heap space
  Exception in thread ""http-bio-8443"-Acceptor-0" java.lang.OutOfMemoryError: Java heap space
  Exception in thread ""http-bio-8080"-exec-3" java.lang.OutOfMemoryError: Java heap space
  Exception in thread "com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread-#4" java.lang.OutOfMemoryError: GC overhead limit exceeded
  </code></pre>
  
  <p>And this is my configuration : </p>
  
  <pre><code>-server -Xms2048m -Xmx2048m
  -XX:NewSize=1024m -XX:MaxNewSize=1024m -XX:PermSize=512m
  -XX:MaxPermSize=1024m -XX:+DisableExplicitGC"
  </code></pre>
  
  <p>Can anyone please point out that am I getting this exceptions because of this configurations or anything else ? </p>
  
  <p>I know that there is some issue in my code but how can I predict out to find those issues ? 
  I have tried Eclipse MAT to analyse memory dumps but didn't get any idea though.</p>
  
  <p>I have already tried to increase memory for this but it didn't help much except just reducing the frequency of this exceptions.</p>
  
  <p>Please help. Thanks in advance.</p>