[GENERAL] JDBC prepared statement is not treated as prepared statement

[高健]

Hello:



I  have one question about prepared statement.

I use Java via JDBC, then send prepared statement to execute.

I thought that the pg_prepared_statments  view will have one record after
my execution.

But I can't find.



Is the JDBC's prepared statement  differ from  SQL execute by prepare
command ?

http://www.postgresql.org/docs/current/static/sql-prepare.html



My simple java program is the following:



import java.sql.*;



public class Test01 {



        public static void main(String argsv[]){

        try

         {

           Class.forName("org.postgresql.Driver").newInstance();

           String url = "jdbc:postgresql://localhost:5432/postgres" ;



           Connection con =
DriverManager.getConnection(url,"postgres","postgres" );



           ///Phase 1:-------------Select data from
table-----------------------





           System.out.println("Phase 1------------------------start");



           String strsql = " select * from customers where cust_id = ?";

           PreparedStatement pst=con.prepareStatement(strsql);



           pst.setInt(1,3); //find the customer with cust_id of 3.



           ResultSet rs = pst.executeQuery();



           while (rs.next())

            {

               System.out.print("cust_id:"+rs.getInt( "cust_id"));

               System.out.println("...cust_name:"+rs.getString( "cust_name"
));

           }

           System.out.println("Phase 1------------------------end\n");







           ///Phase 2:-------------Use connection again,to select data from
data dictionary-----------------------



           System.out.println("Phase 2------------------------start");



           strsql = "select * from pg_prepared_statements";

           pst=con.prepareStatement(strsql);



           rs = pst.executeQuery();



           while (rs.next())

           {

              System.out.println("statement:"+rs.getString( "statement"));

           }

           System.out.println("Phase
2------------------------end\n");



           ///Phase 3:-------------Use connection again,to select data from
table-----------------------



           System.out.println("Phase
3------------------------start");

           strsql = "select * from customers";

           pst=con.prepareStatement(strsql);



           rs = pst.executeQuery();



           while (rs.next())

           {

              System.out.print("cust_id:"+rs.getInt( "cust_id"));

              System.out.println("...cust_name:"+rs.getString( "cust_name"
));

          }



          System.out.println("Phase
3------------------------end\n");



          rs.close();

          pst.close();

          con.close();



       }

        catch (Exception ee)

        {

           System.out.print(ee.getMessage());

       }

        }



}



The result of it's execution is:

Phase 1------------------------start

cust_id:3...cust_name:Taylor

Phase 1------------------------end



Phase 2------------------------start

Phase 2------------------------end



Phase 3------------------------start

cust_id:1...cust_name:Smith

cust_id:2...cust_name:Brown

cust_id:3...cust_name:Taylor

Phase 3------------------------end



That is to say: my prepared statement is not cached by PG?

Then how to write a  java program to made it's prepared statement realized
by PG to treat it as a "prepared statement"?

Thank you.