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I was recently tasked with writing a command-line script in Jruby that performed simple CRUD operations against a simple database table. I’ve written tons of scripts in the past that manipulated tables, but I had never done so using Jruby. I therefore decided to first write a “bare-minimum” test script that would help me dip my toes in this unfamiliar water.

I wanted to write my test script against a database manager that ran on my laptop, but I didn’t want to go through the hassle of installing and configuring Oracle or MySql. Also, I soon learned that a lot of Ruby database drivers don’t work with Jruby, so I needed a small, simple database that had a good JDBC driver. I ended up installing and configuring Apache Derby, and it worked out very well for me.

So anyways, here’s the script (jdbctest.rb):

 require 'java'
 require './derbyclient.jar'
 require './derbytools.jar'

 # This example assumes that you have the free DerbyDB software installed on
 # your machine.  It also assumes that you are running it in "server" mode by
 # executing the startNetworkServer.bat script.

 # This is what I'm using instead of Class.forName("org.apache.derby.jdbc.ClientDriver").newInstance()
 import 'org.apache.derby.jdbc.ClientDriver'

 connString = "jdbc:derby://localhost:1527/MyDbTest"
 conn = Java::JavaSql::DriverManager.getConnection(connString)

 stmt = conn.createStatement

 rs = stmt.executeQuery("select * from derbyDb")

 while (rs.next) do
     puts "#{rs.getString("NUM")} -- #{rs.getString("ADDR")}"
 end

 rs.close
 stmt.close
 conn.close()

I then placed the jdbctest.rb script in a folder with the derbyclient.jar and derbytools.jar file, and then executed the script like this:

 c:\Dev\jruby\somefolder>jruby .\jdbctest.rb
 180 -- Grand Ave.
 1910 -- Union St.

To make this script work, you need to do the following:

1. Install Derby using this tutorial: Step 1 – Install Software
   • This is a very simple task that took me all of 6 minutes after downloading the software.
2. Create the MyDbTest database and the derbyDB table using this tutorial: Step 2 – ij Basics
   • You should also populate this table using the SQL located under the Execute SQL Statements section.
3. Once you’ve created and queried your table using ij, start your Derby server using this tutorial: Step 4 – Derby Network Server
   • You should validate the server using ij. Please see the Test network server connection with ij section in the Step 4 tutorial for help.

Please note that this might seem like a lot of work, but it’s really very simple, especially when you compare it installing and configuring most relational database managers. It took me about 20 minutes from A to Z, and I had no prior experience with Derby.

That’s it! I hope that this tutorial helps a few other people who want to get started with Jruby and JDBC.