refactor(native): lift jthrowable_to_string into shared jni_util module

andygrove · May 19, 2026 · May 18, 2026 · May 18, 2026 · May 18, 2026 · May 18, 2026
commit 484cd12314024110503b0d10c67be754cd8e5731
diff --git a/native/src/jni_util.rs b/native/src/jni_util.rs
@@ -0,0 +1,69 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! Small shared helpers for JNI call sites.
+
+use jni::objects::JThrowable;
+use jni::JNIEnv;
+
+/// Best-effort: extract class name and `getMessage()` from a Java throwable.
+/// Anything that goes wrong collapses to a generic message so we don't
+/// double-throw inside an error path.
+///
+/// `kind` and `name` are used to build the surfaced error message
+/// (e.g., `kind="UDF" name="add_one"` -> `"Java UDF 'add_one' threw ..."`).
+pub(crate) fn jthrowable_to_string(
+    env: &mut JNIEnv,
+    throwable: &JThrowable,
+    kind: &str,
+    name: &str,
+) -> String {
+    let class_name_result = (|| -> jni::errors::Result<String> {
+        let class = env.call_method(throwable, "getClass", "()Ljava/lang/Class;", &[])?;
+        let class_obj = class.l()?;
+        let n = env.call_method(&class_obj, "getName", "()Ljava/lang/String;", &[])?;
+        let n_obj = n.l()?;
+        let n_str: String = env.get_string(&n_obj.into())?.into();
+        Ok(n_str)
+    })();
+    let class_name = match class_name_result {
+        Ok(s) => s,
+        Err(_) => {
+            env.exception_clear().ok();
+            "<unknown exception class>".to_string()
+        }
+    };
+
+    let message_result = (|| -> jni::errors::Result<String> {
+        let msg = env.call_method(throwable, "getMessage", "()Ljava/lang/String;", &[])?;
+        let msg_obj = msg.l()?;
+        if msg_obj.is_null() {
+            return Ok("<no message>".to_string());
+        }
+        let s: String = env.get_string(&msg_obj.into())?.into();
+        Ok(s)
+    })();
+    let message = match message_result {
+        Ok(s) => s,
+        Err(_) => {
+            env.exception_clear().ok();
+            "<no message>".to_string()
+        }
+    };
+
+    format!("Java {} '{}' threw {}: {}", kind, name, class_name, message)
+}
diff --git a/native/src/lib.rs b/native/src/lib.rs
@@ -18,6 +18,7 @@
 mod arrow;
 mod csv;
 mod errors;
+mod jni_util;
 mod json;
 mod proto;
 mod schema;

diff --git a/native/src/udf.rs b/native/src/udf.rs
@@ -28,10 +28,9 @@ use datafusion::error::DataFusionError;
 use datafusion::logical_expr::{
     ColumnarValue, ScalarFunctionArgs, ScalarUDFImpl, Signature, TypeSignature, Volatility,
 };
-use jni::objects::{GlobalRef, JStaticMethodID, JThrowable};
+use jni::objects::{GlobalRef, JStaticMethodID};
 use jni::signature::{Primitive, ReturnType};
 use jni::sys::{jbyte, jlong, jvalue};
-use jni::JNIEnv;
 
 pub(crate) struct JavaScalarUdf {
     pub(crate) name: String,
@@ -230,7 +229,8 @@ impl ScalarUDFImpl for JavaScalarUdf {
                 DataFusionError::Execution(format!("exception_occurred failed: {}", e))
             })?;
             env.exception_clear().ok();
-            let message = jthrowable_to_string(&mut env, &throwable, &self.name);
+            let message =
+                crate::jni_util::jthrowable_to_string(&mut env, &throwable, "UDF", &self.name);
             return Err(DataFusionError::Execution(message));
         }
 
@@ -292,45 +292,3 @@ pub(crate) fn volatility_from_byte(byte: u8) -> datafusion::error::Result<Volati
         ))),
     }
 }
-
-/// Best-effort: extract class name and getMessage() from a Java throwable.
-/// Anything that goes wrong collapses to a generic message so we don't
-/// double-throw inside an error path.
-fn jthrowable_to_string(env: &mut JNIEnv, throwable: &JThrowable, udf_name: &str) -> String {
-    let class_name_result = (|| -> jni::errors::Result<String> {
-        let class = env.call_method(throwable, "getClass", "()Ljava/lang/Class;", &[])?;
-        let class_obj = class.l()?;
-        let name = env.call_method(&class_obj, "getName", "()Ljava/lang/String;", &[])?;
-        let name_obj = name.l()?;
-        let name_str: String = env.get_string(&name_obj.into())?.into();
-        Ok(name_str)
-    })();
-    let class_name = match class_name_result {
-        Ok(s) => s,
-        Err(_) => {
-            // A reflective call itself threw — clear that secondary exception so the
-            // thread is in a clean state when we return to the JVM.
-            env.exception_clear().ok();
-            "<unknown exception class>".to_string()
-        }
-    };
-
-    let message_result = (|| -> jni::errors::Result<String> {
-        let msg = env.call_method(throwable, "getMessage", "()Ljava/lang/String;", &[])?;
-        let msg_obj = msg.l()?;
-        if msg_obj.is_null() {
-            return Ok("<no message>".to_string());
-        }
-        let s: String = env.get_string(&msg_obj.into())?.into();
-        Ok(s)
-    })();
-    let message = match message_result {
-        Ok(s) => s,
-        Err(_) => {
-            env.exception_clear().ok();
-            "<no message>".to_string()
-        }
-    };
-
-    format!("Java UDF '{}' threw {}: {}", udf_name, class_name, message)
-}