Chris' Babble

How to implement DES and Triple DES from scratch

Chris Hulbert — Wed, 04 Aug 2010 09:09:34 +0000

A simple Ruby implementation with lots of comments. This document explains how to implement DES, from the perspective of learning how the algorithm works. Simplicity and learnability are favoured over optimisation unlike most open source crypto code, so hopefully this will make it easier for people to understand and de-mystify DES and block-cipher cryptography in general.

Code can be found here: http://github.com/chrishulbert/crypto

How to Implement DES in Ruby

How to use Cookies in Struts 2 with ServletRequest and ServletResponse

Chris Hulbert — Fri, 30 Jul 2010 05:14:00 +0000

Unlike sessions, it appears that cookies are a bit of an orphaned feature in Struts2. There are ways of reading them using the framework, but no way to write them. Since you have to go directly to the ServletResponse to write cookies, you may as well use the ServletRequest directly to read them while you're at it (IMO); so that's the approach i'm spruiking here.

Firstly, you need access to the ServletRequest and ServletResponse. To get Struts 2 to inject these into your action, you need to implement ServletRequestAware and ServletResponseAware, like so:

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.struts2.interceptor.ServletRequestAware;
import org.apache.struts2.interceptor.ServletResponseAware;

public class MyAction extends ActionSupport implements ServletResponseAware, ServletRequestAware {

  protected HttpServletResponse servletResponse;
  @Override
  public void setServletResponse(HttpServletResponse servletResponse) {
    this.servletResponse = servletResponse;
  }

  protected HttpServletRequest servletRequest;
  @Override
  public void setServletRequest(HttpServletRequest servletRequest) {
    this.servletRequest = servletRequest;
  }
}

Once you've got those interfaces implemented as above, you can use them as below:

public String execute() {
  int division;

  // Save to cookie
  Cookie div = new Cookie("division", String.format("%d",division));
  div.setMaxAge(60*60*24*365); // Make the cookie last a year!
  servletResponse.addCookie(div);

  // Load from cookie
  for(Cookie c : servletRequest.getCookies()) {
    if (c.getName().equals("division"))
      division=Integer.parseInt(c.getValue());
  }

  return "success";
}

This method does not require you to do any configuration in your web.xml nor struts.xml, so don't worry about those. Thanks for reading, hope this helps!

References:
http://stackoverflow.com/questions/3350554/the-struts2-cookies-map-does-not-seem-to-be-getting-set
http://omkarp.blogspot.com/2007/08/working-with-cookies-in-struts-2-part-2.html

How to use sessions with Struts 2

Chris Hulbert — Fri, 30 Jul 2010 05:01:48 +0000

Luckily (unlike cookies), Struts2 comes with features to give you access to sessions without dipping into the realms of the ServletRequest / ServletResponse. So here's how to use sessions with Struts 2:

You need to make your action implement SessionAware to get access to the session:

import com.opensymphony.xwork2.ActionSupport;
import org.apache.struts2.interceptor.SessionAware;

public class MyAction extends extends ActionSupport implements SessionAware {

  // For SessionAware
  Map session;
  @Override
  public void setSession(Map session) {
    this.session = session;
  }

}

Once you've done that, you can access the session with code like this:

public String execute() {
  int division = ...

  // Write to the session
  session.put("division",(Integer)division);

  // Read from the session
  if (session.containsKey("division"))
    division=(Integer)session.get("division");

  return "success";
}

And if you feel like configuring your session lifetimes manually, make the following edits to your web.xml:

Reference:
http://struts.apache.org/2.0.14/docs/how-do-we-get-access-to-the-session.html

Using Quartz Scheduler in a Java web app (servlet)

Chris Hulbert — Tue, 27 Jul 2010 05:45:29 +0000

Lately i've needed to run a background task every 10 seconds in a Java web-app (servlet) and found Quartz Scheduler to be great. It's just that their documentation doesn't really cover servlets much. So here we are:

I'm using Struts2, Spring, and Hibernate, but most of this will apply regardless of framework you choose. Firstly, download and unzip Quartz and copy the quartz-all-*.jar to your WebContent\WEB-INF\lib folder. Then copy all the jar's from the unzipped quartz lib folder in as well.
Edit your web.xml and add the following inside the web-app section:


  org.quartz.ee.servlet.QuartzInitializerListener

Next create a \src\quartz.properties with contents like the below:

# Generic configuration - probably not needed, most of this is just the defaults
org.quartz.scheduler.instanceName = MyScheduler
org.quartz.scheduler.instanceId = 1
org.quartz.scheduler.rmi.export = false
org.quartz.scheduler.rmi.proxy = false
org.quartz.threadPool.class = org.quartz.simpl.SimpleThreadPool
org.quartz.threadPool.threadCount = 10
org.quartz.jobStore.class = org.quartz.simpl.RAMJobStore

# Configure it to look in the quartz.xml for the job schedules
org.quartz.plugin.jobInitializer.class = org.quartz.plugins.xml.XMLSchedulingDataProcessorPlugin
org.quartz.plugin.jobInitializer.fileNames = quartz.xml
org.quartz.plugin.jobInitializer.failOnFileNotFound = true
org.quartz.plugin.jobInitializer.scanInterval = 120

Then create a \src\quartz.xml similarly to below. Of course your xml will be different, but what i've got here is a single job that repeats every 10 seconds forever, the class being 'background.jobs.MyJob':




	

	
		*  
		* 
	

	
		
		true
		
		false
	

	

	
		
			MyJob
			background.jobs.MyJob
		
		
			
				TenSecondIntervals
				MyJob
				-1 
				10000

Finally, you want to create the actual job class with the code to be called periodically. Here's MyJob.java below. You'll notice that i'm implementing StatefulJob instead of plain Job - this is so that if the job is still running when it is due to start again, Quartz won't start another instance of it:

package background.jobs;

import org.quartz.*;
import org.slf4j.*;

public class MyJob implements StatefulJob {

  @Override
  public void execute(JobExecutionContext context) throws JobExecutionException {
    try {

      // Do all my stuff here

    } catch (Exception ex) {
      LoggerFactory.getLogger(getClass()).error(ex.getMessage());
    }
  }
}

Good luck!

Javascript date picker that Doesn't Suck!(tm)

Chris Hulbert — Tue, 27 Jul 2010 03:46:57 +0000

Hi,
I've been fed up with all the JS calendar date pickers that are out there - they're all too complicated, heavy, rely on frameworks that i don't want to include, or they're ugly, or have anti-commercial licenses, etc etc etc. So here's mine:
Download the files here

You can see a demo here

Here's the pros:
* I've tested with IE, Chrome, Firefox, and Safari, and they all seem to work, miraculously.
* Very light: only two extra files needed (about 10k)!
* No extra frameworks needed!
* Not hideously ugly! (IMO)
* Date format is universal - no more confusing d/m/y with m/d/y!
* Very simple to use: include two files in your head, and set a class on your input's.

Here's how to use it. In your page's head, add the following lines:

Whenever you have an input box, set the class to 'datepicker' (or add 'datepicker' to the list of classes), and ensure that the input box has an id, and you're done:

Enjoy!

Using Oracle XE with Hibernate

Chris Hulbert — Tue, 20 Jul 2010 01:36:49 +0000

Recently had to upgrade one of my programs to go from some other database to Oracle. Luckily it uses hibernate, so i thought it would be hassle free. Well, i hit a few hiccups so here's how i finally got it to work. Note that this is for Oracle XE, but should be applicable for any Oracle version 9i onwards.

Here's the hibernate.cfg.xml configuration for connecting to an Oracle XE. Importantly, if you're using hibernate 3.3+ you can skip the dialect setting because it'll auto-detect the dialect beautifully.




  
    
    oracle.jdbc.pool.OracleDataSource
    jdbc:oracle:thin:@myhost:1521/xe
    myusername
    mypassword