An Evolvable Model and Tool Support for Java Exception Handling. Y C Cheng

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1 An Evolvable Model and Tool Support for Java Handling Y C Cheng yccheng@csie.ntut.edu.tw

2 This talk introduces an Java exception handling model and an Eclipse plug-in to guide exception handling design and implementation Problem: background of Java exception handling Solution: a model and tool support Discussion

3 Background and Motivation

4 s are poorly handled in most programs because I want to build a robust software but I'm not sure whether to use checked exception or not I don't know how to handle exception well

5 To assist developers in consistently handling exception, we need Relating exception types with fault tolerance capability to guide exception handling A tool that assists programmers to apply concrete exception handling policies

6 An integrated approach to exception handling in Java is proposed Runtime IrrecoverableRT RT Irrecoverable EH QuickFix & Refactoring Plug-in Unchecked Checked Evolvable exception handling model Eclipse plug-in

7 The Handling Model Runtime IrrecoverableRT RT Irrecoverable Unchecked Checked

8 The model elements is established according to three different aspects Abstract Hierarchy Runtime Application s IrrecoverableRT RT Client s view Irrecoverable Component s view Mechanism s Unchecked Checked Mechanism s view The static view of the model call chain

9 The model evolution: fault reporting, exception handling, and fault tolerance Runtime Runtime IrrecoverableRT RT Runtime IrrecoverableRT RT Irrecoverable Unchecked Checked IrrecoverableRT RT Irrecoverable fault tolerance Unchecked Checked Irrecoverable exception handling evolve Unchecked Checked fault reporting evolve

10 A comparison of the three models Model Handling Attitude Effort Robustness Applicability Fault Reporting Handling Fault Tolerance Checked Low Low Prototyping Unchecked XP methodology Time-to-market Checked Medium Medium Standard Java Unchecked applications Checked High High Callback interface Unchecked Don t believe checked exceptions Special treatment handle ; don t handle

11 Handling Model in Action: JCIS Examples

12 JCIS is a Java continuous integration system checking out projects form CVS for integration 1 CVS host 2 CVS CVS SCM JCIS host build 3 JCIS Resource

13 The three evolvable models are used to cope with two failure scenarios Scenario I (checked exception) : connection break Scenario II (unchecked exception): runtime component failure CVS CVS JCIS 3. build Workspace JCIS 3. build Workspace

14 Fault-tolerant levels in JCIS after applying the three exception handling models Model Scenario System Effect Fault Reporting Handling Fault Tolerance connection break runtime component failure connection break runtime component failure connection break runtime component failure JCIS Resource inconsistency Fail to execute the CVS command JCIS Resource consistency Fail to execute the CVS command JCIS Resource consistency Keep the CVS command running

15 According to the application architecture, an exception view is derived Architecture View View Message Presentation Layer E PIC 5. report Application Layer E 4. report CVSCmdManager Service Layer E ' 3. wrap CVSCheckout Third - party components E 2. rethrow JavaCVS JVM E 1. throw JCIS checkout layered design

16 The result of applying the three exception handling models in the two failure scenarios Model Scenario Handling Fault Reporting connection break (checked) Handling connection break (checked) Fault Tolerance connection break (checked) runtime component failure (unchecked)

17 Fault reporting model try // mechanism codes catch ( e) // fault reporting e.printtracestack(); try // mechanism codes mechanism_api(); catch (FileNotFound e) //converting w/o handling throw new IrrecoverableRT(e); Caught checked and unchecked exceptions Caught at all layers checked exceptions

18 handling model sample code Runtime IrrecoverableRT RT Irrecoverable Unchecked Checked try // mechanism codes mechanism_api(); catch (FileNotFound e) // recover 成功, 離開 try block

19 handling model sample code Runtime IrrecoverableRT RT Irrecoverable Unchecked Checked try // mechanism codes mechanism_api(); catch (FileNotFound e) // fails to recover, caller 需繼續 recover throw new (e);

20 handling model sample code Runtime IrrecoverableRT RT Irrecoverable Unchecked Checked public class Command public void execute() try // mechanism codes mechanism_api(); catch (FileNotFound e) // fails to recover, caller 可以 recover // 但有介面限制 throw new RT(e);

21 handling model sample code Runtime IrrecoverableRT RT Irrecoverable Unchecked Checked try // mechanism codes mechanism_api(); catch (FileNotFound e) // if recover 失敗, caller 無法 recover throw new IrrecoverableRT(e);

22 Fault tolerance model sample code Runtime IrrecoverableRT RT Irrecoverable Unchecked Checked try mechanism_checkedex_api(); catch (FileNotFound e) try // recover 成功, 離開 try block mechanism_uncheckedex_api(); catch (ClassCast e ) // recover 成功, 離開 try block

23 An Eclipse Plug-in for Handling

24 Eclipse Quick Fix provides a primary method to deal with checked exception 1 2 marker A marker indicates an error on Eclipse proposal

25 Our first goal: providing suitable EH proposals according to annotated model setting 1 model setting Model-aware proposals 2

26 Our second goal: providing exception handling refactoring

27 The EH plug-in conceptual diagram Java 5.0 Annotations Model EH plug-in Code Template Final Code Policy Utility classes

The working process of Eclipse Quick Fix 0 creates AST Eclipse Platform 1 4 2

28 The working process of Eclipse Quick Fix 0 creates AST Eclipse Platform invokes returns visits QuickFix Processor 3 creates Proposal [ ] Eclipse Proposal

29 In summary, we presented an exception model and an Eclipse plug-in to aid developers in dealing with exceptions Evolvable Cover both checked and unchecked exceptions Streamline the implementation of exception handling Question?

30 Linked Slides

31 handling is a difficult topic, especially in Java due to the use of checked exceptions Throwable Error Runtime Non-Runtime Any SubClass Any SubClass Any SubClass Unchecked s Checked s Java exception hierarchy The handle-or-declare rule of checked exception

32 Java compilers enforce the handle-ordeclare rule of checked exceptions class FileService handle public copy (String s) throws IO if (error) throw new IO( reason ); declare backup () FileService fs = new FileService(); try fs.copy( a.txt ); catch (IO e) // exception handling code backup () throws IO FileService fs = new FileService(); fs.copy( a.txt );

33 The Java compiler does not enforce any rules for unchecked (runtime) exceptions class FileService public copy (String s) if (error) throw new Runtime( reason ); backup () FileService fs = new FileService(); fs.copy( a.txt );

34 Tool support may be a trap; condering the Eclipse Quick Fix 3 blindly propagate exceptions 1 Error message 2 Default proposals 4 catch but do nothing

Lecture 20. Java Exceptional Event Handling. Dr. Martin O Connor CA166

Lecture 20. Java Exceptional Event Handling. Dr. Martin O Connor CA166 Lecture 20 Java Exceptional Event Handling Dr. Martin O Connor CA166 www.computing.dcu.ie/~moconnor Topics What is an Exception? Exception Handler Catch or Specify Requirement Three Kinds of Exceptions