The second important item we learned from this process is the performance difference between a true SQL index on the iSeries and a keyed logical index. From iSeries V4R2 on, SQL indexes have page sizes of 64k. By comparison, a DDS logical will max out at 32k, and will typically be much smaller. The performance is so much better that our customer is converting all all their DDS logical indexes to SQL, even if only their legacy RPG applications use it. This IBM document has a good discussion of this issue.

Probably the simplest example is connecting to an iSeries system using JDBC to select from some tables, and with the right libraries it is straightforward. It’s also fun to be doing some nifty quick Ruby but with some preexisting and proven Java libraries.

Also, if you use Java and Ruby, definitely put arton’s RubyJavaBridge in your pocket; you’ll end up using it more than once.

What you’ll need:

• Ruby (well yea)
• Java (ok)
• access to an AS400 system (that’s the whole point here…)
  For testing, I’ve been using a free account available from Holger Scherer Software und Beratung.
• jt400.jar jdbc drivers from JTOpen, a great open-source Java library for AS400 access.
• RubyJavaBridge is the keystone for this.

Installing the software is the hardest part of this exercise, but it’s more tedium than anything. Once you’ve got it all downloaded and running the fun can begin.

require 'rjb'
Rjb::load('jtopen_5_0/lib/jt400.jar',['-Djdbc.drivers=com.ibm.as400.access.AS400JDBCDriver'])

DriverManager = Rjb::import('java.sql.DriverManager')

begin
  connection = DriverManager.getConnection('jdbc:as400://as400.holgerscherer.de','YOUR_USERNAME','YOUR_PASSWORD')
  statement = connection.prepareStatement("SELECT count(*) FROM SYSIBM.TABLES")
  result_set = statement.executeQuery

  while(result_set.next())
    puts result_set.getObject(1).toString
  end
ensure
  result_set.close if defined?(result_set) && !statement.nil?
  statement.close if defined?(statement) && !statement.nil?
  connection.close if defined?(connection) && !connection.nil?
end

$ ruby as400_rjb.rb
19138

Very readable, I think. Java and Ruby actually play well together given half the chance and arton’s fantastic bridge.

Compare this with the pure Java implementation.

import java.sql.*;

public class As400Jdbc
{
  public static void main(String args[])
  {
    Connection connection = null;
    try
    {
      connection = DriverManager.getConnection("jdbc:as400://as400.holgerscherer.de","USER","PASS");
      PreparedStatement statement = connection.prepareStatement("SELECT COUNT(*) FROM SYSIBM.TABLES");

      ResultSet resultSet = statement.executeQuery();

      while(resultSet.next())
      {
        System.out.println(resultSet.getObject(1));
      }
    }
    catch(SQLException e)
    {
      throw new RuntimeException(e);
    }
    finally
    {
      try{ if(connection!=null) connection.close(); }
      catch(SQLException e)
      {
        throw new RuntimeException(e);
      }
    }

  }
}

$ javac As400Jdbc.java
$ java -cp jtopen_5_0/lib/jt400.jar:. -Djdbc.drivers=com.ibm.as400.access.AS400JDBCDriver As400Jdbc
19138

The Ruby code and the Java code are nearly one-for-one so far, and that’s fine. Still, let’s see if we can’t pull the Java code more into Ruby’s world. The begin...end stuff gets tiresome; it would be nice if these Java classes could handle the resource allocation and disposal drudgery for us, using blocks.

require 'rjb'
Rjb::load('/home/darren/dload/jtopen_5_0/lib/jt400.jar',['-Djdbc.drivers=com.ibm.as400.access.AS400JDBCDriver'])

DriverManager = Rjb::import('java.sql.DriverManager')
class <<DriverManager
  def with_connection(*args)
    begin
      connection = DriverManager.getConnection(*args)
      yield connection
    ensure
      connection.close
    end
  end
end

DriverManager.with_connection('jdbc:as400://as400.holgerscherer.de','USER_NAME','USER_PASS') do |conn|
  statement = conn.prepareStatement("SELECT count(*) FROM SYSIBM.TABLES")
  result_set = statement.executeQuery()
  result_set.next()
  puts result_set.getObject(1).toString
end

I know I’m a geek because stuff like this makes me giggle. So many worlds are colliding here–Ruby, Java, AS400, DB2, the client system (Linux in this case)–and it all comes together so nicely.

I’m not saying I’d build an app out of this, but it will more than suffice for ad-hoc queries and quick scripts.