Re: Experiences with pl/Java

Thanks to all for providing feedback and sharing opinions. Looks like
you have gone much further on it than I thought someone would have. So I
think I might spend some more time with it, but not plan to use it for
my application in a production environment.

My initial attempts were to try to re-use/port some simple procedures
which are running fine on Apache Derby, but then I got stuck quite early
in the process and could not find documentation showing how things needs
to be done and helping me to understand what I am doing wrong.

My first use case was calling a procedure which does not have any
parameter and this I actually got to run, i.e.

public static String CURRENT_CLIENTID() throws SQLException {

         String vcFKClientID = "000";

         return vcFKClientID;
     }

CREATE OR REPLACE FUNCTION rte."CURRENT_CLIENTID"()
   RETURNS character varying AS
'onlyPostgreSQLPk.Functions.CURRENT_CLIENTID'
   LANGUAGE java VOLATILE SECURITY DEFINER
   COST 100;
ALTER FUNCTION rte."CURRENT_CLIENTID"()
   OWNER TO postgres;

=> select rte."CURRENT_CLIENTID"() returns '000'

My second use case was to create a procedure with an out parameter, i.e.

public static void SP_getNextID(int iNextVal[], String vcIDName)
             throws SQLException {
         Connection conn = getDefaultConnection();

         Statement stmt = conn.createStatement(ResultSet.TYPE_FORWARD_ONLY,
                 ResultSet.CONCUR_UPDATABLE);

         String cSQL = "SELECT \"LastValue\" \n" + "FROM rte.\"TBL_IDs\"
\n"
                 + "WHERE \"IDName\" = '" + vcIDName + "'\n";

         ResultSet rs = stmt.executeQuery(cSQL);

         while (rs.next()) {
             iNextVal[0] = rs.getInt(1) + 1;
             rs.updateInt("LastValue", iNextVal[0]);
             rs.updateRow();
         }

         rs.close();
         stmt.close();

         return;

     }

CREATE OR REPLACE FUNCTION rte."SP_getNextID"(OUT "iNextID" integer, IN
"vcIDName" character varying)
   RETURNS integer AS
'allDatabasesPk.Procedures.SP_getNextID(int[], java.lang.String)'

The static method seems to be found. But when calling the function using
pgadmin and issuing a 'Select rte."SP_getNextID"('xy');' I am getting error
Too many parameters - expected 1
which I find confusing as I am only passing one parameter!?

I tried some variations I could think of, but without success.
Unfortunately I have not found an exmaple anywhere on the web showing
how this needs to be done.

Would be great if someone could have a look at above and spot what I am
doing wrong.

Thanks a lot in advance.

Kind regards
Thomas

Am 19.11.2012 20:19, schrieb Welty, Richard:
> Edson Richter [edsonrichter@hotmail.com] writes:
>> Em 19/11/2012 15:26, Welty, Richard escreveu:
>>> PL/Java requires that the methods being directly called from PostgreSQL are static.
>>> while i don't disagree with the advice, PL/Java is limited in this respect.
>> :-) as I said, I know little about pl/Java... thanks for pointing this out.
>> So, after calling the static method, probably inside the static methods,
>> the programmer will create his/her logic. Writing this logic considering
>> GC behavior would make your apps more stable.
>> I would recommend to not use any Java library that keeps "caches" (ones
>> like EclipseLink or Hibernate), unless you know exactly how to configure
>> caches and soft/weak references - and their limitations.
> i would probably recommend severely limiting what you try to do in PL/Java.
>
> in my particular project, the overall goal was incrementally doing push updates to an Apache
> Solr search engine. this entailed building xml descriptions of the update that was required,
> sending it with an http request (which required untrusted pl/java), and providing a recovery & retry
> mechanism in case the http request failed, which limited itself to using the provided jdbc.
>
> i got it working and working well, but i put a lot of care into insuring that the garbage collecter
> never got stressed very hard and i didn't try to do more than was strictly necessary. i'd argue
> that if you find yourself wanting to use hibernate or eclipselink down in PL/Java, you should
> rethink your application design.
>
> richard
>
>