Stories about Software


Setting Up AJAX and JQuery

AjaxSo, in response to feedback from my previous post about my   home automation server site, I’ve decided to incorporate AJAX and JQuery into my solution. This is partially because it’s The Right Thing ™ and partially because I’m a sucker for the proposition of learning a new technology. So, here are the steps I took toward going from my previous solution to a working one using AJAX, including downloads and other meta-tasks.

The first thing that I did was poke around until I found this tutorial, which is close enough to what I to do to serve as a blueprint. I found it very clear and helpful, but I realized that I had some legwork to do. I setup my java code as per the tutorial, but on the client side in JSP, I realized things wouldn’t work since I couldn’t very well source a jquery library that didn’t exist in the workspace. I poked around on my computer a bit and saw that I did have various jquery.js libraries, but they were part of Visual Studio, Android, and other concerns, so I figured I’d download one specifically for this task rather than try to reappropriate.

So, I went to jquery.com. I poked around a bit until I found the most recent “minified” version, since that’s what the example was using, and discovered it here. I was a little surprised to find that the ‘download’ would consist of copying it and pasting it into a local text file that I named myself, but I guess, what did I expect – this is a scripted language executed by browsers, not a C++ compiler or the .NET framework or something.

In Eclipse, I made a directory under my WebContent folder called “js”, and I put my new jquery-1.7.1.min.js file in it. Now, I had something to link to in my JSP page. Here is the actual link that I put in:

Just to make sure my incremental progress was good, I built and ran on localhost, and

My project now error’d on build and at runtime. For some reason, Eclipse seems not to like the minified version, so I switched to using the non minified. I still got a runtime error in Eclipse browser (though not in Chrome) and the javascript file had warnings in it instead of errors. This was rectified by following the high scoring (though strangely not accepted) answer on this stack overflow post.

However, it was at this point that I started to question how much of this I actually needed. I don’t particularly understand AJAX and JQuery, but I’m under the impression that JQuery is essentially a library that simplifies AJAX and perhaps some other things. The tutorial that I was looking at was describing how to send POST variables and get a response, and how this was easier with JQuery. But I actually don’t need the variables, nor do I need a response at this time. So, given the JQuery runtime errors that were continuing to annoy me, I deleted JQuery from the proiejct and resolved to work this out at a later date. From here, after a bit of poking around, I realized that using AJAX from within Javascript was, evidently, pretty simple. I just needed to instantiate an XMLHttpRequest object and call some methods on it. Here is what I changed my kitchen.jsp page to be:

Pretty simple, though when you have no idea what you’re doing, it takes a while to figure out. 🙂

I instantiate a request, populate it and send it. Given my RESTful scheme, all the info the server needs is contained in the path of the request itself, so it isn’t necessary for me to parse the page or ask for a response. I added the javascript:void(0) calls so that the buttons would still behave like actual, live links. I think that later, when it is, I’ll probably bring JQuery back and revisit the tutorial that I found. Here is my updated controller class.

I’m fairly pleased with the asynchronous setup and the fact that I’m not playing weird games with redirect anymore. I have a unit test project setup, so I think I’m now going to get back to my preference of TDD, and factor the controller to handle more arbitrary requests, making use of an interfaced service for the lights and a data driven model for the different rooms and appliances. I’ve got my eye on MongoDB as a candidate for data storage (I’m not really doing anything relational), but if anyone has better ideas, please let me know.


Redirect Back with Spring 3.0 MVC

As I’m getting back into Java and particularly Spring MVC, it’s a bit of an adjustment period, as it always is when you’re dusting off old skills or trying something new. Things that should be easy are maddeningly beyond your reach. In light of that, I’m going to document a series of small milestones as I happen on them, in the hopes that someone else in my position or a complete newbie might find it useful.

So, today, I’m going to talk about processing a GET request without leaving the page. The reason I wanted to do this is that I have a page representing my house’s kitchen. The page has two buttons (really links styled as buttons through CSS) representing lights on and off. I’m providing a restful URL scheme to allow them to be turned on and off: kitchen/on and kitchen/off will turn the lights on and off, respectively. However, when this happens, I don’t have some kitchen/off.jsp page that I want handling this. I want them redirected right back to the kitchen page for further manipulation, if need be.

Here is how this was accomplished. Pay special attention to the kitchen() method taking the variable name and request as paramters:

So, the idea here is that I’m returning a redirect to the referrer. So, basic logic flow is that client sends an HTTP get request by clicking on the link. We process the request, take appropriate action, and then redirect back to where he started.

This certainly may not be the best way to accomplish what I’m doing, but it’s a way. And, my general operating philosophy is to get things working immediately, and then refactor and/or optimize from there. So, if you know of a better way to do it, by all means, comment. Otherwise, I’ll probably figure one out on my own sooner or later.


Setting Up Spring MVC 3.0

Why Spring MVC?

It’s been a while since I’ve done a lot with Java. I’ve been writing an Android app and see and interact with just enough Java not to forget what it looks like, but for the last couple of years, I’ve mainly worked in .NET with C#. Today, I started on actual development of my home automation server in earnest (will be added to github shortly). One of the main design goals of this home automation effort is to support affordable solutions and, toward that end, I am designing it to run on bare bones Linux machines, thus allowing old computers to be re-appropriated to run it.

This is the driving force in my choice of implementation tools. It needs to be runnable on Linux and Windows, and to have a small footprint. But, it also needs to support a true object oriented design paradigm and rich server side functionality. So, I will be dusting off my J2EE and using Spring MVC and Java for the server itself.

Setting up Spring MVC 3.0

I’ve been spoiled by developing principally in .NET over the last couple of years. In that world, any kind of project is usually a Visual Studio install and a plugin or NuGet package away. In the open source world of Spring and Java, it’s not quite as straightforward. My first step was, of course, a hello world app. I have plenty of Spring MVC/J2EE experience, but I was last developing with Spring when it was version 1.x, and we’re a few years removed and on 3.1, so I’m basically starting all over.

I already had Eclipse and Tomcat installed, and I set about finding an Eclipse plugin for creating a sample spring project or a tutorial on the same. I didn’t really find either. The most helpful thing I found, by far, was this blog post. If you take steps to satisfy the preconditions listed and follow the blog itself, you’ll be most of the way there.

I had to take two additional steps to get my new Spring “Hello World” project up and running. I had to get commons-logging.jar from the spring framework that I had downloaded and put it into my little app’s Web-INF\lib folder. I then had to do the same with jstl.jar from my Tomcat installation. Only after doing that was Hello World up and running.

Hopefully, this saves someone reading some time.