CallMethodViaReflection¶

Overview¶

CallMethodViaReflection is a Spark Catalyst expression that enables calling static methods on Java classes via reflection from SQL queries. It provides a bridge between Spark SQL and arbitrary Java code by allowing dynamic method invocation with type conversion and error handling.

Syntax¶

reflect(className, methodName, arg1, arg2, ...)

Arguments¶

Argument	Type	Description
className	String (foldable)	Fully qualified Java class name containing the static method
methodName	String (foldable)	Name of the static method to invoke
arg1, arg2, ...	Various supported types	Arguments to pass to the method (optional)

Return Type¶

Always returns StringType - the result of calling String.valueOf() on the method's return value.

Supported Data Types¶

Input arguments support the following data types:

BooleanType
ByteType
ShortType
IntegerType
LongType
FloatType
DoubleType
StringType (with collation support)

Algorithm¶

The expression evaluation follows these steps:

Validates that the specified class exists and can be loaded via reflection
Locates the target static method matching the provided method name and argument types
Converts Spark internal data types to appropriate Java objects (UTF8String to String)
Invokes the method using Java reflection with the converted arguments
Wraps the result using String.valueOf() and converts to UTF8String for return

Partitioning Behavior¶

This expression has no impact on partitioning:

Preserves existing partitioning as it operates row-by-row
Does not require shuffle operations
Marked as Nondeterministic which may affect certain optimizations

Edge Cases¶

Null handling: Returns null if any required argument is null or if method invocation fails (when failOnError is false)
Class loading: Throws compilation error if the specified class cannot be found or loaded
Method resolution: Throws compilation error if no matching static method is found for the given signature
Type conversion: Only UTF8String arguments are converted to Java String; other types are passed as-is
Exception handling: Method invocation exceptions return null when failOnError=false, otherwise propagate

Code Generation¶

This expression uses CodegenFallback, meaning it does not support Tungsten code generation and always falls back to interpreted evaluation mode for safety with reflection operations.

Examples¶

-- Call UUID.fromString() method
SELECT reflect('java.util.UUID', 'fromString', 'a5cf6c42-0c85-418f-af6c-3e4e5b1328f2');
-- Returns: a5cf6c42-0c85-418f-af6c-3e4e5b1328f2

-- Call Math.max() with integer arguments  
SELECT reflect('java.lang.Math', 'max', 10, 20);
-- Returns: 20

-- Call System.getProperty() 
SELECT reflect('java.lang.System', 'getProperty', 'java.version');
-- Returns: current Java version string

// DataFrame API usage
import org.apache.spark.sql.functions.expr

df.select(expr("reflect('java.lang.Math', 'abs', -42)").as("absolute_value"))

// Using column references
df.select(expr("reflect('java.lang.String', 'valueOf', some_column)").as("string_value"))