HeartSaVioR commented on a change in pull request #27025: [SPARK-26560][SQL] 
Spark should be able to run Hive UDF using jar regardless of current thread 
context classloader
URL: https://github.com/apache/spark/pull/27025#discussion_r399612923
 
 

 ##########
 File path: 
sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveSessionCatalog.scala
 ##########
 @@ -66,49 +66,52 @@ private[sql] class HiveSessionCatalog(
       name: String,
       clazz: Class[_],
       input: Seq[Expression]): Expression = {
-
-    Try(super.makeFunctionExpression(name, clazz, input)).getOrElse {
-      var udfExpr: Option[Expression] = None
-      try {
-        // When we instantiate hive UDF wrapper class, we may throw exception 
if the input
-        // expressions don't satisfy the hive UDF, such as type mismatch, 
input number
-        // mismatch, etc. Here we catch the exception and throw 
AnalysisException instead.
-        if (classOf[UDF].isAssignableFrom(clazz)) {
-          udfExpr = Some(HiveSimpleUDF(name, new 
HiveFunctionWrapper(clazz.getName), input))
-          udfExpr.get.dataType // Force it to check input data types.
-        } else if (classOf[GenericUDF].isAssignableFrom(clazz)) {
-          udfExpr = Some(HiveGenericUDF(name, new 
HiveFunctionWrapper(clazz.getName), input))
-          udfExpr.get.dataType // Force it to check input data types.
-        } else if 
(classOf[AbstractGenericUDAFResolver].isAssignableFrom(clazz)) {
-          udfExpr = Some(HiveUDAFFunction(name, new 
HiveFunctionWrapper(clazz.getName), input))
-          udfExpr.get.dataType // Force it to check input data types.
-        } else if (classOf[UDAF].isAssignableFrom(clazz)) {
-          udfExpr = Some(HiveUDAFFunction(
-            name,
-            new HiveFunctionWrapper(clazz.getName),
-            input,
-            isUDAFBridgeRequired = true))
-          udfExpr.get.dataType // Force it to check input data types.
-        } else if (classOf[GenericUDTF].isAssignableFrom(clazz)) {
-          udfExpr = Some(HiveGenericUDTF(name, new 
HiveFunctionWrapper(clazz.getName), input))
-          udfExpr.get.asInstanceOf[HiveGenericUDTF].elementSchema // Force it 
to check data types.
+    // Current thread context classloader may not be the one loaded the class. 
Need to switch
+    // context classloader to initialize instance properly.
+    Utils.withContextClassLoader(clazz.getClassLoader) {
+      Try(super.makeFunctionExpression(name, clazz, input)).getOrElse {
+        var udfExpr: Option[Expression] = None
+        try {
+          // When we instantiate hive UDF wrapper class, we may throw 
exception if the input
+          // expressions don't satisfy the hive UDF, such as type mismatch, 
input number
+          // mismatch, etc. Here we catch the exception and throw 
AnalysisException instead.
+          if (classOf[UDF].isAssignableFrom(clazz)) {
+            udfExpr = Some(HiveSimpleUDF(name, new 
HiveFunctionWrapper(clazz.getName), input))
+            udfExpr.get.dataType // Force it to check input data types.
 
 Review comment:
   I figured out above code doesn't give error - HiveFunctionWrapper stores 
`instance` which is copied in `makeCopy()` - so once the instance is created it 
doesn't seems to require changing classloader.
   
   That said, below code gives error:
   
   ```
   // uses classloader which loads clazz
   val udf = HiveGenericUDTF(name, new HiveFunctionWrapper(clazz.getName), 
input)
   // make sure HiveFunctionWrapper.createFunction is not called here
   
   val newUdf = 
udf.makeCopy(udf.productIterator.map(_.asInstanceOf[AnyRef]).toArray)
   // change classloader which doesn't load clazz
   newUdf.dataType
   ``` 
   
   we force call `.dataType` after creating HiveXXXUDF, so if my understanding 
is correct it won't be matter.
   
   Could you please check whether my observation is correct, or please let me 
know if I'm missing something?

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