SQL & PL/SQL

Hi All,
Was not sure weather to post this on Java forum threads or PL/SQL forum threads. So posting at both locations.

I have to call a PL/SQL procedure from java. This PL/SQL has IN/OUT parameters as well as return a Boolean value.
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The procedure definition is as follows:

FUNCTION GET_NEXT(O_error_message IN OUT VARCHAR2,
IO_item_no IN OUT ITEM_MASTER.ITEM%TYPE,
I_item_type IN ITEM_MASTER.ITEM_NUMBER_TYPE%TYPE)
return BOOLEAN;
END ITEM_NUMBER_TYPE_SQL;
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And the java function I am using is as follows:
This is in the ADF Application module impl code

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public String callNextItem(){
CallableStatement callableStmt = null;
String rmsUser = getDBTransaction().getConnectionMetadata().getUserName();
String callableStatement = "begin ? := ITEM_NUMBER_TYPE_SQL.VALIDATE_FORMAT(?,?,?); end;";
System.out.println("callableStatement "+callableStatement);
try{
callableStmt = getDBTransaction().createCallableStatement(callableStatement,0);
callableStmt.registerOutParameter(1, Types.*BIT*);
callableStmt.registerOutParameter(2, Types.VARCHAR);
callableStmt.registerOutParameter(3, Types.VARCHAR);
callableStmt.registerOutParameter(4, Types.VARCHAR);
callableStmt.setBoolean(1, false);
callableStmt.setString(2, "");
callableStmt.setString(3, "");
callableStmt.setString(4, "UPC-A");
callableStmt.executeUpdate();
System.out.println("STATUS : " + callableStmt.getString(3));
System.out.println("ERROR : " + callableStmt.getString(2));
String status = "";
getDBTransaction().commit();
System.out.println("commited ");
callableStmt.close();
return status;
}catch(SQLException e){
System.out.println("Error:" +e);
throw new JboException(e);
}
}
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But this function never works. Throws "not valid expression type" error.

I have called several PL/SQL procedures before, only difference being
they never used to return any value. Particularly I feel the cause of the
error is the Boolean type that is returned from the procedure.

If you have any idea, please help.