ObjectInspector

ObjectInspector is an abstraction used in Apache Hive's SerDe API to inspect and manipulate the internal representation of data values stored in Hive tables. It provides a uniform way to access values regardless of how they are serialized or stored, enabling processing logic to operate on data in a type-safe manner without depending on a specific storage format.

The ObjectInspector framework defines a hierarchy of inspectors for primitive types and for complex types such as structs, lists, maps, and unions. Each inspector knows the type category of the data it handles and offers mechanisms to access the value and, for complex types, to examine or extract nested components (for example, fields within a struct, elements of a list, or values within a map). Inspectors also facilitate conversion between the internal representation and their corresponding Java objects used by UDFs and other processing components.

Key roles of ObjectInspector include supporting user-defined functions, SerDe implementations, and the Hive runtime in retrieving data from rows, performing type-aware operations, and converting to Java representations when needed. This abstraction allows Hive to support multiple storage formats and serialization schemes while maintaining a consistent data access model.

Commonly used implementations include PrimitiveObjectInspector for primitive types and StructObjectInspector, ListObjectInspector, MapObjectInspector, and UnionObjectInspector for complex types. Inspectors often provide metadata such as the type category, field names, and type information, aiding in dynamic data processing and schema discovery.

In summary, ObjectInspector enables Hive to separate data storage details from data processing logic, providing a flexible, extensible way to inspect and extract values across diverse data formats and schemas.