The document discusses garbage collection and object graphs. It lists objects and their outgoing references, showing how objects are connected and retained in memory. It also covers how Log4j must be configured for proper cleanup in web applications to avoid issues.

1. #JCConf

2. •
•
•
•
•
•
•
•

3. •
•
•
•

6. •
•
•
•

7. #JCConf

9. https://www.youtube.com/watch?v=450maTzSIvA

13. 13

16. #JCConf

19. •
–
•
•
–
•
•
–

21. A B
C
D E
F G
H
A and B are garbage collection roots,
(GC roots)
Leading Set Retained Set
E E, G
C C, D, E, F, G, H
A, B A, B, C, D, E, F, G, H

23. A B
C
D E
F G
H

24. A B
C
D E
F G
H

26. A B
C
D E
F G
H

28. A B
C
D E
F G
H

29. #JCConf

33. Done

34. More Things…

35. List objects → with outgoing references

37. oracle.jdbc.ScrollableResultSet → scrollStmt
→ sqlObject → sqlBytes → Copy → Value

38. SELECT * FROM POP.PRMASTER,POP.PRITEM WHERE
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
…………………………………………………..…………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
…………………………………………………………Order By PRITEM.IDOCNUMBER
DESC,PRITEM.ITEM

39. Merge Shortes Paths to GCRoots
→ exclude all phantom/weak/soft etc. references

41. List objects → with outgoing references

42. Sorting by Class Name

43. java.lang.Thread → org.apache.catlina.connector.Request
→ postData → Copy → Value

44. sessionid=16F098C27D8DE1C8C7E58A15798C470A&applicantID=&hcreatorID=&
applicantName ………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
…………………………………………………………………………..…………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………………………………………………………
………………………………………………………………………………… KOLON_prodhier=K0

45. HTTP Request Attributes
org.apache.catlina.connector.Request → attributes →
table → java.util.HashMap$Entry

46. HTTP Session Data
org.apache.catlina.connector.Request → session → attributes
→ segments → java.util.concurrent.ConcurrentHashMap$Segment

47. Java Basics → Thread Overview and Stacks

49. •
•
•
•

50. •
•
•
•

51. #JCConf

52. •
–
•
–
•

57. Merge Shortest Paths to GC Roots
→ exclude all phantom/weak/soft etc. references

59. List objects → with outgoing references

60. Expand the node

61. target
org.apache.logging.log4j
.core.util.DefaultShutdownCallbackRegistry

62. Using Log4j 2 in Web Applications
You must take particular care when using Log4j or any other logging framework within a Java EE web application.
It's important for logging resources to be properly cleaned up (database connectionsclosed, files closed, etc.)
when the container shuts down or the web application is undeployed. Because of the nature of class loaders within web applications,
Log4j resources cannot be cleaned up through normalmeans. Log4j must be "started" when the web application deploys and "shut down"
when the web application undeploys. How this works varies depending on whether your application is
a Servlet 3.0 or newer or Servlet 2.5 web application.
In either case, you'll need to add the log4j-web module to your deployment as detailed in the Maven, Ivy, and Gradle Artifacts manualpage.
To avoid problems the Log4j shutdown
hook will automatically be disabled
when the log4j-web jar is included.

64. <classloader>
org.apache.logging.log4j.core.jmx.StatusLoggerAdminMBean

65. •

67. •
•
–
–
•
–

68. #JCConf

69. •
•
•
•
•
•

70. /* */ public abstract class ItemFactory
/* */ implements Constants
/* */ {
/* */ protected static Logger a;
/* 45 */ public Map b = null;
/* */ public static int c;
/* */ private static String[] A;
/* */
/* */ protected ItemFactory()
/* */ {
/* 51 */ this.b = Collections.synchronizedMap(new HashMap());
/* 52 */ if ((ItemBean.d) || (a == null)) {
/* 53 */ a = Logger.getLogger(A[2]);
/* */ }
/* */ }
Bad news: It is obfuscated (混淆)
Can’t decompile, rewrite, and compile …

71. •
public aspect ItemFactoryAop {
private final static int DEFAULT_CACHE_SIZE = 100000;
after() : execution(workflow.ItemFactory.new()) {
((ItemFactory)thisJoinPoint.getThis()).b =
Collections.synchronizedMap(
new cache.LruCache(DEFAULT_CACHE_SIZE));
}
}

72. •
–
•
–
•
•

73. #JCConf

74. •
•
•
•
•

78. •
•
•
–

79. #JCConf

80. •
•
•
•

81. #JCConf

82. MayYour JVM
Live Long and Prosper