How to implement Oracle User-Defined Aggregate Functions in Java

Question

As Oracle manual says

You can create a user-defined aggregate function by implementing a set of routines collectively known as the ODCIAggregate routines. You can implement these routines as methods within an object type, so the implementation can be in any language that Oracle supports, PL/SQL, C, C++ or Java .

There is no other info how to implement it. I have found example of implementing this in C/C++

Anyone know how to accomplish this using Java? Any info would be great.

Answer 1

Yes a Java implementation of Oracle aggregate function is indeed possible. The enabling trick is not to use a Java implementation of an ORACLE TYPE but to define a PL/SQL wrapper package above the Java class and use the PL/SQL functions in the TYPE implementation.

Very simple implementation of a Hello World Java based aggregate function follows - the aggregate function returns always a string "Hello World".

The Java class makes nearly nothing only returns in the ODCITerminate function the string "Hello World".

Any practical implementation on a Java based aggregate function will need to set up a context class and pass it to each iterate method.

Java Class

Create or Replace AND RESOLVE Java Source Named "JAggrFun" As
import java.math.BigDecimal;

class JAggrFun {
/*
Supporting Java class for dummy aggregate function
Implemented methods:
initiate   - dummy
iterate    - dummy
terminate  - return "Hello World"
merge (is not required)

*/
  final static BigDecimal SUCCESS = new BigDecimal(0);
  final static BigDecimal ERROR = new BigDecimal(1);

  static public BigDecimal ODCIInitialize(BigDecimal[] sctx) {

    return SUCCESS; 
  }

  static public BigDecimal ODCIIterate(BigDecimal ctx, String str) { 

     return SUCCESS;                                                                 
  } 

  static public BigDecimal ODCITerminate(BigDecimal ctx, String[] str) {

    str[0] = "Hello World";
    return SUCCESS;
  } 

}
/

wrapper package of Java methods

create or replace
PACKAGE JAggrFunPackage authid current_user AS
  FUNCTION ODCIInitialize(
                  ctx OUT NOCOPY NUMBER
                  ) RETURN NUMBER
                  AS LANGUAGE JAVA
    NAME 'JAggrFun.ODCIInitialize(
              java.math.BigDecimal[]) return java.math.BigDecimal';

  FUNCTION ODCIIterate(
                  ctx IN NUMBER,
                  str VARCHAR2) RETURN NUMBER
                  AS LANGUAGE JAVA
    NAME 'JAggrFun.ODCIIterate(
              java.math.BigDecimal,
              java.lang.String) return java.math.BigDecimal';

  FUNCTION ODCITerminate(
                  ctx IN NUMBER,
                  str OUT VARCHAR2) RETURN NUMBER
                  AS LANGUAGE JAVA
    NAME 'JAggrFun.ODCITerminate(
              java.math.BigDecimal,
              java.lang.String[]) return java.math.BigDecimal';

END JAggrFunPackage;
/

Type

CREATE OR REPLACE 
TYPE JAggrFunPackageType authid current_user AS OBJECT
  (  
   jctx NUMBER, -- stored context;  not used in dummy implementation
   STATIC FUNCTION
        ODCIAggregateInitialize(sctx IN OUT NOCOPY JAggrFunPackageType )
        RETURN NUMBER,

   MEMBER FUNCTION
        ODCIAggregateIterate(self IN OUT NOCOPY JAggrFunPackageType,
                             VALUE IN VARCHAR2 )
        RETURN NUMBER,

   MEMBER FUNCTION
        ODCIAggregateTerminate(self IN JAggrFunPackageType,
                               returnValue OUT NOCOPY VARCHAR2,
                               flags IN NUMBER)
        RETURN NUMBER, 

   MEMBER FUNCTION
        ODCIAggregateMerge(self IN OUT NOCOPY JAggrFunPackageType,
                           ctx IN JAggrFunPackageType)
        RETURN NUMBER
);
/

Aggregate Function

CREATE OR REPLACE 
FUNCTION JAggr(input VARCHAR2 )
RETURN VARCHAR2
AGGREGATE USING JAggrFunPackageType;
/

Type Body

create or replace
type body JAggrFunPackageType  is
  static function ODCIAggregateInitialize(sctx IN OUT NOCOPY JAggrFunPackageType)
  return number
  is
  begin
    sctx := JAggrFunPackageType( null );
    return ODCIConst.Success;
  end;

  member function ODCIAggregateIterate(self IN OUT NOCOPY JAggrFunPackageType,
                                       value IN varchar2 )
  return number
  is
     status  NUMBER;
  begin
    if self.jctx is null then

      status := JAggrFunPackage.ODCIInitialize(self.jctx);
      if (status <> ODCIConst.Success) then
         return status;
      end if;
    end if;

    status := JAggrFunPackage.ODCIIterate(jctx,value);

    return status;
  end;

  member function ODCIAggregateTerminate(self IN JAggrFunPackageType,
                                         returnValue OUT NOCOPY VARCHAR2,
                                         flags IN number)
  return number
  is
  begin

    return JAggrFunPackage.ODCITerminate(jctx, returnValue);
  end;

  member function  ODCIAggregateMerge(self IN OUT NOCOPY JAggrFunPackageType,
                           ctx IN JAggrFunPackageType)
  return number
  is
  begin
    return ODCIConst.Success;
  end;
end;
/

Test

select JAggr(dummy) from dual;

JAGGR(DUMMY)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
-------------
Hello World