搞懂java例外處理的難題：checked與unchecked exceptions不再是問題
DESCRIPTION
討論Java語言中checked與unchecked exceptions使用上的問題TRANSCRIPT
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系統不穩定
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Problem
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Problem
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• Correctness – Contract Specification(超出範圍)
• Robustness – Exception Handling
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RuntimeException
Throwable
Exception Error
Unchecked Exception
Checked Exception
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handle
declare
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• Checked exceptions for recoverable conditions –打死不知道要如何去recover 任何東東？
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class FileService {
…
public copy (String s)
throws IOException {
…
if (error)
throw new
IOException(“reason”);
}
}
backup () {
FileService fs = new
FileService();
try {
fs.copy(“a.txt”);
}
catch (IOException e){
// exception handling code
}
}
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• 我就是不喜歡checked exception，咬我啊!
• 例如，Standard Widget Toolkit (SWT, Eclipse的UI元件)只使用unchecked exception：
– SWTException用來表示可修復的SWT錯誤。
– SWTError則用來表示不可修復的錯誤。
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Spring
Framework
Java
Your
application
checked
unchecked DataAccessException
SQLException
technology-
specific
HibernateException
technology-
specific
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• Exception Type
• Recoverability
• Application Context
• Robustness Level
– G1: Error-reporting (錯誤回報）
– G2: State-recovery (狀態回復）
– G3: Behavior-recovery (行為回復）
• Exception Handling Policy
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練習1: 如果Accepter收到一個 IOException，鄉民們第一個反應是什麼？
練習2: 如果Accepter收到一個 RuntimeException，鄉民們第一個反應是什麼？
Presentation
Layer
Application
Layer
Service Layer E 2. rethrow
4. wrap
Message
5. report
3. recover
E'
E''
JVM1. throwE
AppWin
GameServer
Acceptor
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練習3: 如果Accepter收到一個 IOException，鄉民們該如何處置？
練習4: 如果Accepter收到一個 RuntimeException，鄉民們該如何處置？
Presentation
Layer
Application
Layer
Service Layer E 2. rethrow
4. wrap
Message
5. report
3. recover
E'
E''
JVM1. throwE
AppWin
GameServer
Acceptor
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練習5: 如果Accepter收到一個 IOException，鄉民們該如何處置？
練習6: 如果GameServer收到 IOException ，鄉民們該如何處置？
Presentation
Layer
Application
Layer
Service Layer E 2. rethrow
4. wrap
Message
5. report
3. recover
E'
E''
JVM1. throwE
AppWin
GameServer
Acceptor
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練習7: Accepter的RL要設為多少？
練習8: GameServer的RL要設為多少?
Presentation
Layer
Application
Layer
Service Layer E 2. rethrow
4. wrap
Message
5. report
3. recover
E'
E''
JVM1. throwE
AppWin
GameServer
Acceptor
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練習9: Acceptor這一層有哪些policy可用？
練習10: GameServer這一層有哪些policy可用?
Presentation
Layer
Application
Layer
Service Layer E 2. rethrow
4. wrap
Message
5. report
3. recover
E'
E''
JVM1. throwE
AppWin
GameServer
Acceptor
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