Java 例外處理壞味道與重構技術
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The document discusses exception handling issues in a credit scoring system application and proposes refactoring solutions. It describes problems like ignored checked exceptions, unprotected main programs causing unexpected termination, and lack of failure atomicity. The refactoring aims to replace ignored exceptions, add try-catch blocks, eliminate dummy handlers, and introduce checkpoints to improve robustness. Statistics show the refactoring reduced maintenance costs by 89.8% due to fewer failures.
![18
static public void main(String[] args) {
/* some code */
}
↓
static public void main(String[] args) {
try {
/* some code */
}
catch (Throwable e) {
/* displaying and/or logging the exception */
}
}
Copyright@2013 Teddysoft](https://image.slidesharecdn.com/javaehsmellsrefactorings-published-130418042844-phpapp02/85/Java-18-320.jpg)
Java 例外處理壞味道與重構技術
- 3. 3 系統不穩定
- 4. 4
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- 8. 8 Problem
- 9. 9 Problem
- 11. • Correctness – Contract Specification(超出範圍) • Robustness – Exception Handling Copyright@2013 Teddysoft
- 16. 16 EH smell Refactoring Ignored checked exception Replace Ignored Checked Exception with Unchecked Exception Unprotected main program Avoid Unexpected Termination with Big Outer Try Block Dummy handler Replace Dummy Handler with Rethrow Nested try block Replace Nested Try Block with Method Ignored checked exception, Dummy handler Introduce Checkpoint Class Spare handler Introduce Resourceful Try Clause Copyright@2013 Teddysoft
- 17. public void writeFile(String fileName, String data) { Writer writer = null; try { writer = new FileWriter(fileName); /* may throw an IOException */ writer.write(data); /* may throw an IOException */ } catch (IOException e) { /* ignoring the exception */ } } ↓ public void writeFile(String fileName, String data) { Writer writer = null; try { writer = new FileWriter(fileName); /* may throw an IOException */ writer.write(data); /* may throw an IOException */ } catch (IOException e) { throw new UnhandledException(e, “message”); } } 17 Copyright@2013 Teddysoft
- 18. 18 static public void main(String[] args) { /* some code */ } ↓ static public void main(String[] args) { try { /* some code */ } catch (Throwable e) { /* displaying and/or logging the exception */ } } Copyright@2013 Teddysoft
- 19. 19 catch (AnException e) { e.printStackTrace(); } ↓ catch (AnException e) { throw new UnhandledException(e, “message”); } Copyright@2013 Teddysoft
- 20. 20 FileInputStream in = null; try { in = new FileInputStream(…); } finally { try { if (in != null) in.close (); } catch (IOException e) { /* log the exception */ } } ↓ FileInputStream in = null; try { in = new FileInputStream(…); } finally { closeIO (in); } private void closeIO (Closeable c) { try { if (c != null) c.close (); } catch (IOException e) { /* log the exception */ } } Copyright@2013 Teddysoft
- 21. 21 public void foo () throws FailureException { try { /* code that may change the state of the object */ } catch (AnException e) { throw new FailureException(e); } finally {/* code for cleanup */} } ↓ public void foo () throws FailureException { Checkpoint cp = new Checkpoint (/* parameters */); try { cp. establish (); /* establish a checkpoint */ /* code that may change the state of the object */ } catch (AnException e) { cp.restore (); /* restore the checkpoint */ throw new FailureException(e); } finally { cp.drop(); } } Copyright@2013 Teddysoft
- 22. 22 try { /* primary */ } catch (SomeException e) { try {/* alternative */} catch(AnotherException e) { throw new FailureException(e); } } ↓ int attempt = 0; int maxAttempt = 2; boolean retry = false; do { try { retry = false; if (attempt == 0) { /* primary */ } else { /* alternative */ } } catch (SomeException e) { attempt++; retry = true; if (attempt > maxAttempt) throw new FailureException (e); } } while (attempt<= maxAttempt && retry) Copyright@2013 Teddysoft
- 24. • CSS is a banking application for checking customers’ credit history in processing their loan applications 24 Credit Scoring System (CSS) Gateway (IBM Message Queue) Joint Credit Information Center (JCIC) Authentication (Domino Server) Other Applications Copyright@2013 Teddysoft
- 25. • The use of exceptions and return code were mixed in an arbitrary manner • Many checked exceptions were caught and ignored • Unchecked exceptions were not caught which lead to an unexpected termination of the JSP program • Failure atomicity of each component was not investigated 25 Copyright@2013 Teddysoft
- 26. • Bug fixing is a strong force drawing the developer’s attention to deal with exceptions • Cost-effectiveness measurements can be provided to convince the management to support the refactoring – Improving quality, saving maintenance cost, and increasing customer satisfaction 26 Copyright@2013 Teddysoft
- 27. Reported failure Failing operation/ possible reason Failure count Current restoration actions Restoration time per failure Cannot make a connection to Domino server User login/ Connections of Domino Internet Inter-ORB Protocol (DIIOP) were exhausted. It was likely that DIIOP connections were not correctly disposed. 125 1. Rebooting Domino server 2. Rebooting CSS About 20 minutes MQ server connection is broken Sending request to JCJS/ MQ connections were exhausted. Perhaps they were not properly released. 66 1. Rebooting MQ Server 2. Rebooting CSS About 10 minutes Cannot send messages to MQ server Sending request to JCJS/ There were two possible reasons: Message queue was full. Gateway was offline due to maintenance or crash. 10 1. Rebooting MQ Server 2. Rebooting CSS About 10 minutes 27
- 28. 28 Credit Scoring System (CSS) Gateway (IBM Message Queue) Joint Credit Information Center (JCIC) Authentication (Domino Server 1) Other Applications Authentication (Domino Server 2) X Copyright@2013 Teddysoft
- 29. 29 Reported failure Failure count from Sep. 2005 to Dec. 2005 Failure count from Sep. 2006 to Dec. 2006 Sep. Oct. Nov. Dec. Sep. Oct. Nov. Dec. Cannot make a connection to Domino server 13 5 9 14 10 5 0 0 MQ Server connection broken 6 1 4 8 3/0 0 1/0 0 Cannot send messages to MQ Server 0 0 0 2 3/0 1/0 0 0 Copyright@2013 Teddysoft
- 30. 30 Code type Total vs. modified code Modification percentage Non-commented line of code 14150/371 2.63% Catch clauses 855/21 2.46% Copyright@2013 Teddysoft
- 31. 31 Task Man-hours Sum Collecting bugs reports in 2005 10 18 (43.9%) Refactoring cost (Code review) 7 (30.4%) Refactoring cost (Exception Handling goal analysis) 4 (17.4%) Refactoring cost (Coding) 3 (13%) Refactoring cost (Testing) 9 (39.2%) Total man-hours in applying refactoring 23 (56.1%) Total man-hours in improving robustness 41 (100%) Copyright@2013 Teddysoft
- 32. 32 Cost element Cost calculation Maintenance cost in 2005 201 (failure) * 2 (hours) * 100 (US$) = 40,200 (US$) Refactoring cost 41 (man-hours) * 100 (US$) = 4,100 (US$) Maintenance cost saving in the following year (money) 40,200 (US$) – 4,100 (US$) = 36,100 (US$) Maintenance cost saving in the following year (percentage) 36,100 (US$) / 40,200 (US$) * 100 = 89.8% Copyright@2013 Teddysoft
- 33. 33Copyright@2013 Teddysoft EH smell Refactoring Ignored checked exception Replace Ignored Checked Exception with Unchecked Exception Unprotected main program Avoid Unexpected Termination with Big Outer Try Block Dummy handler Replace Dummy Handler with Rethrow Nested try block Replace Nested Try Block with Method Ignored checked exception, Dummy handler Introduce Checkpoint Class Spare handler Introduce Resourceful Try Clause