Etter mange tiår med programvareutvikling skulle man tro at de fleste applikasjoner håndterer feil på en god måte. I realiteten blir exceptions slukt, kastet på nytt, innpakket, ignorert og tilfeldig logget - om de i det hele tatt er tenkt på. Denne sesjonen viser tilnærminger som fungerer og noen tommelfingerregler for feilhåndtering, samt fallgruver og grusomme eksempler. Vi diskuterer også checked exceptions - et eksperiment i Java - og forklarer hvorfor de bør unngås. http://javazone.no/incogito/session/Riktig+feilh%C3%A5ndtering+(og+ja,+checked+exceptions+er+skadelige).html

1. Riktig feilhåndtering
...og ja, checked exceptions er skadelig
Trond Arve Wasskog – JavaZone 2008

2. 0
Feilhåndtering

3. Exception handling done right (and yes, checked exceptions are not necessary!)
- Trond Arve - BEKK - Confluence
[JavaSpecialists 162] - Exceptions in Java
Unchecked Exceptions — The Controversy (The Java™ Tutorials > Essential
Classes > Exceptions)
java.net: Exception-Handling Antipatterns
java.net: Three Rules for Effective Exception Handling
Java Exceptions Handling
The Art and Craft of Great Software Architecture and Development: Java
Exception Handling Anti-Patterns
Neal Gafter's blog: Closures for Java
Neal Gafter's blog: Removing Language Features?

4. Exception handling problems in Java, Part I
Exception handling problems in Java, Part II
Bruce Eckel's MindView, Inc: Does Java need Checked Exceptions?
Exceptions in Java: Nothing exceptional about them - Java World
News & Ideas Forum (Closed for new topic posts) - Failure and Exceptions
The Trouble with Checked Exceptions
BEKK forum :: View topic - Håndtering av exceptions - erfaringer/diskusjoner
Thinking Inside a Bigger Box » A Hopeful Idea: The End of Checked
Exceptions?
Should checked exceptions be removed from Java?
The RedirectException - The Daily WTF

5. Dont Use Exceptions For Flow Control
Exception Patterns
Exception Tunneling
Checked Exceptions Are Of Dubious Value
Octopull/Java: More Exceptional Java
Java theory and practice: The exceptions debate
James Gosling Chimes In on Checked Exceptions
Exception handling - Wikipedia, the free encyclopedia
cat /dev/random » Remove checked exceptions?
Java's checked exceptions were a mistake (and here's what I would like to do
about it)

6. DOTNET Archives -- November 2000, week 1 (#349)
Java Practices -> Checked versus unchecked exceptions
Java Exception Handling - BEKK - Confluence
Java Exception Handling - BEKK - Confluence
Feilhåndtering - Prosjektkvalitet - Confluence
XO.NET-metoden - Unntakshåndtering - BEKK - Confluence
The Coad Letter: Modeling and Design Edition, Issue 90, Exceptional Strategies
Effective Java Exceptions
cache:DxQf_u_Vue8J:dev2dev.bea.com/lpt/a/541 java exception design
strategies - Google-søk
David Walend's Blog: Design For Exceptions

7. SwTech.com - Java Design Patterns
Single Sign On - Login
Exception Patterns
Page 2 - Framework Patterns: Exception Handling, Logging, and Tracing
Alexander Klimetschek's Blog : Exception Handling Best Practices Part 1
towards_xcptn_hndling.pdf (application/pdf Object)
Andre's Java Links
JForum - Få slutt på galskapen: Stem "ja" til å fjerne checked exceptions fra
Java
Beware the dangers of generic Exceptions - Java World
Designing with exceptions - Java World

8. Forward - Tips and Guidelines for Programming Java GUI Applications
warning unchecked exception - Google-søk
Exception (Java 2 Platform SE v1.4.2)
LISTSERV 15.0 - RMI-USERS Archives
Google Answers: The origin of checked exceptions
Java (programming language) - Wikipedia, the free encyclopedia
Hacking Architect : Weblog
Old News: Java Checked vs. Unchecked Exceptions « Bees Are Social By Nature
Opinion: Exception Handling Debate is Back
Manageability - The Exception Debate: Why Gosling and Hejlsberg are Both In
Error

9. Mistaeks I Hav Made: Generic Throws: Another Little Java Idiom
DataAccessException.gif (GIF Image, 916x397 pixels)
Antonio Goncalves' Weblog
A Test-Driven Exploration of the Advanced Features of EJB 3.0

10. Dårlig feilhåndtering er vanlig

11. 1972
Return
Codes

12. 1964
On Error
Exceptions

13. Return
Codes
On Error
Exceptions
1964 1972 1983 1992 1995 2001

14. Return
Codes
Exceptions
On Error
Exceptions
1964 1972 1983 1992 1995 2001

15. Return
Codes
Checked
Exceptions
Exceptions
On Error
Exceptions
1964 1972 1983 1992 1995 2001

16. Return
Codes
Checked
Exceptions
Exceptions
Exceptions
On Error
Exceptions
1964 1972 1983 1992 1995 2001

17. Java Exceptions
Throwable

18. Java Exceptions
Throwable
Exception
Checked
Exceptions

19. Java Exceptions
Throwable
Exception
Runtime
Checked
Exception
Exceptions
Unchecked
Exceptions

20. Java Exceptions
Throwable
Error Exception
VM Errors Runtime
Checked
(Unchecked) Exception
Exceptions
Unchecked
Exceptions

21. Et alternativt design
Throwable
<interface>
Error Unchecked Exception
Exception
VM Errors Unchecked Checked
Exceptions Exceptions

22. 1
Hvem bryr seg om feilhåndtering?

23. Brukeren er opptatt av at en feil har
oppstått og at situasjonen er håndtert,
ikke hva som har skjedd

24. Forretningen forstår funksjonelle feil og
vil unngå kritiske feil

25. Drift vil vite hva de skal gjøre med feilen

26. Utviklere vil vite hva som har skjedd, hvor,
når, hvorfor, hvem, tilstand og kontekst

27. Feilhåndtering har ulike interessenter med
sine spesifikke behov
Typisk er få representert som kravstillere

28. 2
Feilhåndtering

29. Hva kan man gjøre når en feil oppstår?

30. Ignorere?

31. Håndtere?

32. Prøv igjen?

33. Prøv et alternativ?

34. Avslutte forespørselen

35. Hvor skal feil håndteres?

36. Lokal feilhåndtering

37. Sentral feilhåndtering

38. De aller fleste applikasjoner er tjent med
sentral feilhåndtering

39. Feilhåndtering vs feilretting

41. Hva skjer om en
annen Exception
eller Error
kastes?

43. Er det viktig at
operasjonen eller
applikasjonen
fungerer?

44. Feilhåndtering
sørger for
konsistens

45. Feilhåndtering er kritisk for applikasjonen

46. Automatisert feilretting er ofte
komplekst, kostbart og risikabelt

47. Feilhåndtering er viktigere enn feilretting

48. 3
Tre feiltyper

49. Application Exception

50. System Exception

51. Programming Exception
a.k.a
RuntimeException

52. Type Håndter Feilfiks og Prøv igjen?
utrulling
Application Mulig Nei Nei
Exception
System Nei Nei Mulig
Exception
Programming Nei Ja Nei
Exception

53. 4
Overordnet Design

54. Lettvekts exception-hierarki - Distribuert

55. Felles exception-klasser med feilkode - Sentralisert
java.lang
RuntimeException
AbstractException
- Long id
ApplicationException SystemException

56. Hybrid – Sentrale exception-klasser, distribuert hierarki
java.lang
RuntimeException
AbstractException
- Long id
ApplicationException SystemException
dd dd
<Application Exceptions> <System Exceptions>

57. AbstractException
-Long id
- Map context
-----------------------------
addContext(key, value)

58. Rammeverk = Distribuert
Applikasjon = Sentralisert

59. 5
Checked Exceptions

61. Ondskapens akse
Jim James Ann
Waldo Gosling Wollrath
There was a time when Oak and the earliest version of Java did not have
checked exceptions. Exception handling was advisory, and it was an
unsafe world out there. It was our group (Jim Waldo and I in particular :-)
that recommended that there be exceptions checked by the compiler. Jim
was quite persuasive in his arguments, telling of a world where robust
code would reign. After some consideration, Java was retooled to have
checked exceptions. Only those exceptions for which there was no
recovery or reflect application errors would be unchecked (e.g.,
OutOfMemoryError, NullPointerException respectively). And the world
was safe again
-- Ann Wollrath
http://archives.java.sun.com/cgi-bin/wa?A2=ind9901&L=RMI-USERS&P=R25037

62. Ringbærerne
Item 58: Use chekced exceptions for recoverable conditions
and runtime exceptions for programming errors
Item 59: Avoid unnecessary use of checked exceptions
-- Joshua Bloch
I believe the language could be simplified by treating all
exception types as unchecked without breaking existing
programs. This could also result in a simplification of future
language extensions and APIs. But would the language and
platform be better off without checked exceptions?
-- Neil Gafter
The overhead of checked exceptions was having the opposite
effect of what was intended, something that can happen when
you experiment (and I now believe that checked exceptions were
an experiment based on what someone thought was a good idea,
and which I believed was a good idea until recently).
-- Bruce Eckel

63. Source: http://java.net/pub/pq/163

64. “Checked exceptions are gold.
Developers that don't like them are
those that are too lazy to actually
think about error cases.”
http://www.javaworld.com/javaforums/showflat.php?Cat=0&Number=35228&Main=2629

65. “Were all exceptions unchecked,
no exceptions would be caught
until the corresponding bugs
began to present themselves.”
http://www.javaworld.com/javaforums/showflat.php?Cat=0&Number=35228&Main=2629

66. “Checked exceptions seem like a
really good idea at first…
However, the kind of code you
must write around these things and
the common phenomenon of
"swallowed" exceptions begins to
suggest there's a problem. ”
http://www.mindview.net/Etc/Discussions/CheckedExceptions

67. “I am so tired of all the comments
singing the praise of checked
exceptions on a theoretical basis. I
don’t care about what’s good in
theory!”
http://www.javaworld.com/community/?q=comment/reply/1128

68. “The HibernateException, which wraps most of
the errors that can occur in a Hibernate
persistence layer, is an unchecked exception
(it wasn't in older versions of Hibernate).
In our opinion, we shouldn't force the
application developer to catch an
unrecoverable exception at a low layer. In
most systems, unchecked and fatal exceptions
are handled in one of the first frames of the
method call stack”
http://www.hibernate.org/hib_docs/reference/en/html/transactions.html

69. Checked exceptions
forurenser APIet

70. Checked exceptions fører til
unnamanøvre som forpester
koden

71. Checked exceptions påtvinger
lokal ”feilhåndtering”

72. java.text.ParseException
java.net.MalformedURLException
java.lang.CloneNotSupportedException

73. Checked exceptions kan brukes
når klienten alltid både kan og må
håndtere feilen.

74. God feilhåndtering er viktig
Exceptions er bra
Dokumenter feilsituasjoner

75. Skal kompilatoren påtvinge
feilhåndtering?

78. Checked exceptions påfører
applikasjoner stor skade
Checked exceptions bør fjernes

79. 6
Slik, ikke slik!

80. Ikke bruk exceptions for normal
forretningslogikk

82. Bruk eksisterende exceptions

83. IllegalStateException
UnsupportedOperationException
IllegalArgumentException
NoSuchElementException
NullPointerException

84. Ikke sluk exceptions

89. Fallgruver med try-catch-finally

94. Dokumenter exceptions

97. Russisk kone

99. ERROR [btpool0-3] JDBCExceptionReporter.logExceptions(78) | Violation
of unique constraint $$: duplicate value(s) for column(s) $$: SYS_CT_88 in statement [insert into
app_user (id, account_expired, account_locked, address, city, country, postal_code, province,
credentials_expired, email, account_enabled, first_name, last_name, password, password_hint, phone_number,
username, version, website) values (null, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?
org.springframework.dao.DataIntegrityViolationException: could not insert: [edu.ksu.model.User]; nested
exception is org.hibernate.exception.ConstraintViolationException: could not insert: [edu.ksu.model.User]
at
org.springframework.orm.hibernate3.SessionFactoryUtils.convertHibernateAccessException(SessionFactoryUtils.java:
624)
at
org.springframework.orm.hibernate3.HibernateAccessor.convertHibernateAccessException(HibernateAccessor.java:412)
at org.springframework.orm.hibernate3.HibernateTemplate.doExecute(HibernateTemplate.java:424)
at
org.springframework.orm.hibernate3.HibernateTemplate.executeWithNativeSession(HibernateTemplate.java:374)
at org.springframework.orm.hibernate3.HibernateTemplate.saveOrUpdate(HibernateTemplate.java:744)
<snip/>
Caused by: org.hibernate.exception.ConstraintViolationException: could not insert: [edu.ksu.model.User]
at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:71)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
<snip/>
Caused by: java.sql.SQLException: Violation of unique constraint $$:
duplicate value(s) for column(s) $$: SYS_CT_88 in statement [insert into app_user (id, account_expired,
account_locked, address, city, country, postal_code, province, credentials_expired, email, account_enabled,
first_name, last_name, password, password_hint, phone_number, username, version, website) values (null, ?, ?, ?,
?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)]
at org.hsqldb.jdbc.Util.throwError(Unknown Source)
at org.hsqldb.jdbc.jdbcPreparedStatement.executeUpdate(Unknown Source)
at
org.apache.commons.dbcp.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:101)
at
org.apache.commons.dbcp.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:101)
at org.hibernate.id.insert.AbstractSelectingDelegate.performInsert(AbstractSelectingDelegate.java:33)
... 143 more

100. Unngå både logging og kasting

102. Drift trenger unik feilkode for å
identifisere feilen

104. Utviklere trenger unik instans-ID
for å identifisere feilen

106. Exceptions skal også testes

109. Bruk stubber for testing av
eksterne systemer

110. <Stub>
Fagsystem A
<interface> <interface>
Fagsystem A Fagsystem A
Fagsystem A

111. Gjør logging enkelt

112. Gjør logging enkelt

113. Legg til kontekst der feilen oppstår

114. Takk for oppmerksomheten!
trond.arve.wasskog[at]bekk.no
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