Definitive Guide to Working With Exceptions in Java
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This document serves as a comprehensive guide on working with exceptions in Java, emphasizing the importance of exception handling strategies such as logging and using runtime exceptions. It discusses historical context, best practices, and patterns to effectively manage exceptions in Java applications, while also tackling common anti-patterns. Additionally, it highlights the use of features introduced in recent Java versions, such as Optional and functional interfaces.
![126 © VictorRentea.ro
a training by
class YourException extends RuntimeException {
public enum ErrorCode {
GENERAL,
PHONE_ALREADY_REGISTERED,
...
}
private final ErrorCode code;
private final Object[] params;
...
}
Error Messages
Any case not required to report
messages.properties
GENERAL = Oups!
PHONE_ALREADY_REGISTERED = The phone {0} is assigned to another user
Checkatstartup
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Definitive Guide to Working With Exceptions in Java
- 1. 107 © VictorRentea.ro a training by The Definitive Guide to Working with Exceptions in Java [email protected] ♦ ♦ @victorrentea ♦ VictorRentea.ro Code: https://github.com/victorrentea/exceptions-guide.git
- 2. Victor Rentea Clean Code Evangelist VictorRentea.ro/#playlist 100% Independent Trainer & Consultant Founder of Bucharest Software Craftsmanship Community Simple Design, Refactoring, TDD Java Champion 14 years of Java JS/TS PHP Scala C#, C++ Kotlin Join for free webinars: victorrentea.ro/community
- 3. Technical Training Hibernate/JPASpring Func Prog in Java & more 300+ days2000 devs8 years VictorRentea.rovictorrentea.teachable.com 40 companies Follow me: 30K 4K 3K Java PerformanceReactive-X Design Patterns DDD Clean Code Refactoring Unit Testing TDD any lang
- 4. ... or for You: victorrentea.teachable.com [email protected] Training for your Company: victorrentea.ro
- 5. VictorRentea.ro111 A bit of history
- 6. 112 © VictorRentea.ro a training by At the beginning There were no functions
- 7. 113 © VictorRentea.ro a training by At the beginning There were no exceptions
- 8. 114 © VictorRentea.ro a training by 40 years ago, in C: int errno = f(...); The Age of Libraries 25y, Java: Checked vs Runtime 35y, C++: Invisible exceptions
- 9. 115 © VictorRentea.ro a training by We don't Recover In web apps today, when handling exceptions,This talk is NOT about library development
- 10. 116 © VictorRentea.ro a training by Checked Exceptions
- 11. 117 © VictorRentea.ro a training by code
- 12. 118 © VictorRentea.ro a training by Diaper Anti-Pattern } catch (Exception e) { // TODO waste nights } a.k.a. Exception Swallowing Shawarma-style Exception-Handling Including Runtime bugs= catches all the sh*t
- 13. 119 © VictorRentea.ro a training by throws try catch (Exception t) {/*surprise!*/} RuntimeExceptions won the War ! (except for recoverable? errors thrown by libraries) because we don’t see them Why should I know about that IOException ?
- 14. 120 © VictorRentea.ro a training by } catch (SomeCheckedException e) { throw new SomeRuntimeException(e); } Ignore recurrent exception? (eg. a file poller) log.trace(e.getMessage())
- 15. 121 © VictorRentea.ro a training by } catch (SomeCheckedException e) { throw new SomeRuntimeException(e); } } catch (SomeCheckedException e) { throw new SomeRuntimeException(e); } e.printStackTrace();log.error(e.getMessage(), e); System.err might NOT be logged!
- 16. 122 © VictorRentea.ro a training by } catch (SomeCheckedException e) { throw new SomeRuntimeException(e); } TERROR What if no one logs it? Same exception logged multiple times Log-Rethrow Anti-Pattern Real Solution log.error(e.getMessage(), e);
- 17. 123 © VictorRentea.ro a training by Legacy Code Global Exception Handler Logs and reports any unhandled exceptions Core of Your App Only RuntimeExceptions allowed Checked -> Runtime old lib
- 18. 124 © VictorRentea.ro a training by Presenting Errors to Users What to show them? Exception's message int enum How to unit-test that? How about MVC? Not developer-friendly Finite-set Never a Stack Trace: Security
- 19. 125 © VictorRentea.ro a training by code
- 20. 126 © VictorRentea.ro a training by class YourException extends RuntimeException { public enum ErrorCode { GENERAL, PHONE_ALREADY_REGISTERED, ... } private final ErrorCode code; private final Object[] params; ... } Error Messages Any case not required to report messages.properties GENERAL = Oups! PHONE_ALREADY_REGISTERED = The phone {0} is assigned to another user Checkatstartup _fr _ro _es
- 21. 127 © VictorRentea.ro a training by Global Exception Handler Logs and reports any unhandled exceptions selectively catch only recoverable cases (x-rare) Checked -> Runtime = the only valid reason for creating more exception types Keep Stack Traces from reaching the UI/API
- 22. 128 © VictorRentea.ro a training by Catch-Rethrow-with-Debug Pattern ➢ Searching for hints in the log above? ➢ Breakpoints? Why? To find the value of some variable. } catch (AEx e) { log.error("Debug info " + id); throw new BEx(e); } } catch (AEx e) { throw new BEx("Info " + id, e); } Must-Have Never decapitate the exceptions! Debugging an Exception
- 23. 129 © VictorRentea.ro a training by 4 Reasons to Catch-rethrow User-visible exceptions (code) Tests (code) Developers (+debug info) Wrapping a Checked (into a runtime) @SneakyThrows (Lombok lib)
- 24. 131 © VictorRentea.ro a training by The Queen Of All Exceptions
- 25. 132 © VictorRentea.ro a training by
- 26. 133 © VictorRentea.ro a training by I've never seen you looking so lovely as you did tonight, I've never seen you shine so bright, I've never seen so many men ask you if you wanted to dance, Looking for a little romance, given half a chance, And I have never seen that dress you're wearing, Or the highlights in your hair that catch your eyes, I have been blind; = P1 production Incident The Lady In Redby Chris De Burgh = on-call bug = unsolved for years = spend the night with you = although they lack the knowledge/skills = 50-lines stack-trace = the DEBUG logs before it N P E
- 27. 135 © VictorRentea.ro a training by ➔ Useful message in Java 15
- 28. 136 © VictorRentea.ro a training by NPE How do you fight it ? Throw early Optional
- 29. 138 © VictorRentea.ro a training by Optional<> For functions that might not return anything
- 30. 139 © VictorRentea.ro a training by You, defeating the Null Monster Customer.getMemberCard(): Optional<MemberCard> Entity Getters returning Optional for NULLABLE fields of an Entity
- 31. 140 © VictorRentea.ro a training by Java 8
- 32. 142 © VictorRentea.ro a training by Java 8 Functional Interfaces (eg Function, Predicate, ...) don't declare any checked exceptions. Methods throwing checked are painful to use with Stream API
- 33. 143 © VictorRentea.ro a training by code
- 34. 144 © VictorRentea.ro a training by Mmm.. Higher-order Functions! Convert functions to Rethrow as Runtime Function<..> Unchecked.function(CheckedFunction<..> f) (jOOL lib)
- 35. 145 © VictorRentea.ro a training by Try<>(vavr lib) Can hold either a result or an exception Use to collect both results and exceptions in one pass
- 36. 146 © VictorRentea.ro a training by Key Points • Use Runtime; @SneakyThrows; Unchecked (jool) • Anti-Patterns: Diaper and Log-Rethrow • Enum error codes for users or tests • Global Exception Handler • Catch-Rethrow-with-Debug • Defeating NPE with early-throw, or Optional • Try (vavr) ➔ my 'Functional Design Patterns' talk at Devoxx Belgium
- 37. 147 © VictorRentea.ro a training by Left-Over • Async exceptions (Executors, @Async, CompletableFuture, Reactive-X) • finally {throw} • AutoCloseable.close() {throw} –> Suppressed Exceptions – link • throw before mutating object state • Don't use exceptions for flow control (as a GOTO statement) • InterruptedException – link • Sealed classes + records + Switch Template Matching Java 16+
- 38. 148 © VictorRentea.ro a training by Company Training: [email protected] For You: victorrentea.teachable.com Questions or Follow: