LantaoJin opened a new pull request, #94:
URL: https://github.com/apache/datafusion-java/pull/94
## Which issue does this PR close?
- Closes #55 .
## Rationale for this change
When a Java-implemented upcall throws — scalar UDFs via
`JniBridge.invokeScalarUdf`, table providers via `JniBridge.invokeTableScan` —
the native side captures only `class.getName()` and `getMessage()` via
`jthrowable_to_string` and surfaces it as `DataFusionError::Execution(...)`.
Since #81 routes that through to a typed `ExecutionException`, but the original
Java stack trace is gone by then. A user whose UDF throws
`NullPointerException` deep inside `evaluate(...)` sees:
```
ExecutionException: Java UDF 'my_func' threw java.lang.NullPointerException
```
with no way to find the failing line in their own code. The information
*exists*; it's just discarded.
## What changes are included in this PR?
This PR captures the Java-formatted trace (via
`Throwable.printStackTrace(PrintWriter)` to a `StringWriter`) and appends it to
the existing message. Verbosity is configurable per `SessionContext` so
production paths that treat exception bodies as untrusted user input can opt
out:
```java
SessionContext.builder()
.exceptionVerbosity(ExceptionVerbosity.MESSAGE) // FULL (default),
MESSAGE, NONE
.build();
```
The default is `FULL` -- the issue's stated default -- so callers who don't
touch the setter immediately gain stack traces with no API change.
Out of scope (called out in #55, deferred):
- Cause-chain attachment (the original `Throwable` as `cause` on the typed
`ExecutionException` from #81). Needs a registry-handle for the throwable that
survives the JNI return; complementary follow-up.
## Are these changes tested?
Yes. 10 new tests in `ExceptionVerbosityTest`.
## Are there any user-facing changes?
Yes, additive only -- **default behaviour does change**: the message string
surfaced inside `ExecutionException.getMessage()` now includes the Java stack
trace below the existing `"Java UDF 'name' threw class: message"` header.
Callers that already only `startsWith("Java UDF '...' threw")`-style match keep
working; anything stricter (an exact-equals on the message) would need the new
`MESSAGE` verbosity to lock the pre-#55 format.
- New public type `ExceptionVerbosity`.
- New `SessionContextBuilder.exceptionVerbosity(...)` setter; default
unchanged for callers that don't invoke it (their *behaviour* changes — they
now get traces by default).
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