The board of a large organisation appoints a CIO who delegates technical decisions to his employees. In the Enterprise Architecture (EA) department, an expert on Business Intelligence (BI) decides that the strategy for this company is to have a single Enterprise Data Warehouse (EDW). This makes sense, because experience has shown that in the long run, it is cheaper and more efficient to build one Data Warehouse, rather than start by building "islands" and then later try to merge them together. In the mean time, some business people working for the company have rallied the budget holders, and started a project to build a new online sales application. They need to generate some reports based on the sales from this application, in order to set themselves targets and measure their performance. But, they are not experts when it comes to reporting. The business sector at which their application is aimed is cutting edge and brand new, so they don't know what to expect, they don't really know what kind of reports they will need, and they will certainly need to adapt to the market very quickly. A project team in the IT department then get the assignment to build the application, including the report generation. Also knowing little about reporting, they start talking to EA, who set up a meeting, between themselves, the development team, some people from the Quality Assurance (QA) department and some experts from the BI team. Hours of discussion later, they have made the following conclusions:…
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Persistent State Machine with Apache SCXML
The source code for this blog article can be downloaded here. I'm bored of reinventing the wheel. Everytime I need a state machine to ensure my states traverse only valid transitions, I find myself either not bothering, because I trust my coding (and write all the necessary unit tests of course), or writing very similar code over again. So I started wondering if there was a configurable state machine out there somewhere, and in no time at all Google gave me a link to SCXML from Apache. Apache SCXML is an implementation of a configurable state machine based on the SCXML working draft from W3C. I started by taking a look at what it does and how it works, always keeping in mind my requirements based on previous projects. The main question was how I could use a state machine in a persistent entity so that when an attempt is made to change the state, the state machine validated the attempt, ensuring only valid transitions are carried out. That meant two things: The state machine had to be able to have its current state set to any state. If I load an object with state out of the database, I need to be able to set that state in the state machine so that it checks any attempts to change state, based on this starting state. The state machine had to fit into a JPA entity class so that I could persist and load the state. Apache SCXML doesn't come…
Waffle Theorem
Eating a waffle, I just developed a new theorem. First assume the waffle is square and made up of little squares. If, like me, you eat around two edges, one square deep, so that the waffle stays square, you ALWAYS eat an odd number of squares. Eg. 6x6, you eat 6 mini squares, follwed by 5, making 11 (odd number), so that the waffle itself stays square, now only 5x5. My theorem hypothesises that this is true for all waffle sizes. In fact it's called the "Waffle Theorem", and here is the mathematical proof: y = x^2 - (x-1)^2 -> y = x^2 - (x^2 - 2x + 1) -> y = 2x-1. QED, because 2 times anything ("2x") is always even, and subtracting one ("-1") always makes an even number odd. Hence my hypothesis holds true, regardless of waffle size. Not bad for a Sunday night, all I wanted to do was eat the damn waffle... I have to say though, it's this kind of thing that I love about maths. ----------------- (c) 2010 Ant Kutschera
Taking Advantage of Parallelism
A while ago some colleagues attended a lecture where the presenter introduced the idea that applications may not take full advantage of the multi-core servers which are available today. The idea was that if you have two cores but a process which is running on a single thread, then all the work is done on one single core. Application servers help in this respect, because they handle multiple incoming requests simultaneously, by starting a new thread for each request. So if the server has two cores it can really handle two requests simultaneously, or if it has 6 cores, it can handle 6 requests simultanously. So multi-core CPUs can help the performance of your server if you have multiple simultaneous requests, which is often the case when your server is running near its limit. But it's not often the case that you want your servers running close to the limit, so you typically scale out, by adding more nodes to your server cluster, which has a similar effect to adding cores to the CPU (you can continue to handle multiple requests simultaneously). So once you have scaled up by adding more cores, and scaled out by adding more servers, how can you improve performance? Some processes can be designed to be non-serial, especially in enterprise scenarios. The Wikipedia article on multi-core processors talks about this. Imagine a process which gathers data from multiple systems while preparing the data which it responds with. An example would be a pricing system. Imagine…
GlassFish v3, JSF and Virtual Servers
Anyone wanting to run a JSF app on GlassFish may run into problems when migrating to production, if they are hosting multiple domains on their servers by using virtual hosts! The default deployment, deploys your app to all virtual servers (except _asadmin). If you do that, you get lots of errors, and the app doesn't run. The solution is easy, simply add the --virtualservers argument to the "deploy" command in the "asadmin" console, and supply the relevant virtual server (just the one). Hopefully this will get fixed in GFv3.1!
Oracles Sun Forums Are Crap
Rant Time: I've run in with the forum moderators before, but this really winds me up. I searched on Google for "java open browser", to remind myself which API to call to open the default browser, and the number one search result was this: http://forums.sun.com/thread.jspa?threadID=679673 The answer is at the bottom of the page. Perfect. But then Darryl Burke comes along and locks the thread, because he reckons this latest posting is useless. Sorry, but Sun Forum Moderators don't get the concept of how forums are searched and used! They once told me they lock the threads because they want you to post new threads. I don't have the time to make a new thread asking a question every time I can't solve something, and then wait and hope someone with the answer comes along over the next few days - I want to search for it ,and find the answer immediately. If they keep locking threads, you end up with hundereds of old locked threads which don't help anyone. What their vision is doing, is simply destroying the internet! Idiots! And that is one reason I don't post to their forums anymore - they are the losers, not me.
GlassFish 3 In 30 Minutes
The aim: Set up a simple Java EE 6 project on GlassFish v3 in no time at all. The project must include: email, JMS, JPA, web and EJB (session bean, message driven bean and a timer bean). It must also include security and transactions. Sounds like a lot, but thanks to Java Enterprise Edition version 6, setting up a project like this and configuring all the resources in the Application Server are really easy! I chose GlassFish because its open source, has a useful little Admin Console and I've never developed with it before. Before I started I downloaded Java SE 6 (update 20), Mysql Server, the Mysql JDBC Driver and the GlassFish Tools Bundle for Eclipse, which is a WTP Version of Eclipse 3.5.1 with some specific bundles for developing and deploying on GlassFish. The process I wanted to implement was simple: a user goes to a website, clicks a link to a secure page and logs in, after which a message is persisted to the database and an asynchronous email gets sent. The user is shown a confirmation. In the background theres also a task which reads new messages from the database and updates them so they are not processed a second time. The design was to use a servlet for calling a stateless session EJB, which persists a message using JPA and sends a JMS message to a message driven bean for asynchronous processing. The MDB sends an email. A timer EJB processes and updates any messages…
Auto-update of Midlets
Any professional application should be capable of updating itself over the internet. Even Midlets! The idea is fairly easy in that the Midlet needs to make a call to the server to check what version the latest software has, and compare that to the installed version. If there is a newer version available, then it needs to start the (mobile) device's browser and point it at the URL of the new JAD file. The device will take care of the download and installation after that. So, the following article shows you exactly how this can be implemented. First off, refer to the previous article, which described a framework for making server calls. The sequence diagram looks like this: Based on the framework, the following JSP can be installed serverside, which reads the version number out of the JAD file: <%@page import="java.io.FileInputStream"%> <%@page import="java.io.RandomAccessFile"%> <%@page import="java.io.File"%> <%@page import="java.util.List"%> <html> <body> <% RandomAccessFile raf = null; try{ String version = null; String path = request.getSession().getServletContext().getRealPath("index.jsp"); File f = new File(path); f = f.getParentFile(); f = new File(f, "jads/nameOfJad.jad"); raf = new RandomAccessFile(f, "r"); String curr = null; while((curr = raf.readLine()) != null){ if(curr.startsWith("MIDlet-Version:")){ version = curr.substring(16); break; } } %>OK <%=version%>| add other master data like the users details, their roles, etc. here... <% }catch(Exception e){ log.warn("failed to read master data", e); %>ERROR <%=e.getMessage() %> <% }finally{ if(raf != null) raf.close(); } %> </body> </html> This JSP is called when the Midlet starts, and effectively delivers "master data" to the device, such…
Choosing a Model/Event Pattern
The following diagrams show different implementation patterns of models and corresponding events, as typically used in the UI. Depending upon your needs, you can use the following tables to decide which pattern to implement. The patterns are split into model patterns and event patterns. Not all combinations of the patterns make sense, but patterns can be combined to fulfill your unique requirements. At the end I make some recommendations. Model Pattern 1 - Automatic Event Firing With the above pattern every change to the model results in an event being fired. Typically if the focus of a text field is lost, the model gets set (in Eclipse RCP perhaps using databinding). Any views that show this model attribute get notified and update themselves. Works well for cases where multiple views of the same model need to be continuously up to date. A big disadvantage is the number of events which get fired. You also need to watch out for cyclic dependencies whereby an event updates a second view, and that update fires another event which updates the first. UI performance can suffer with this pattern, because its granularity is simply too fine. Model Pattern 2 - Manual Event Firing This pattern lets the caller (typically the controller) fire an event after it has finished updating all parts of the model. Typically the controller performs any validation of multiple fields, may call the server and when everything is good, updates the UI's model. An example might be when an input…
Transfer-Encoding: chunked
The J2ME HTTPConnection which comes with MIDP lets you make HTTP requests to your server. It doesn't do much at a high level, for example the API doesn't have methods like addCookie() - you need to manually add them with a request header. But the implementation is clever enough to turn any request body which is greater than around 2Kb into a chunked request. With HTTP 1.0, the request had to contain a header called Content-Length which told the server how many bytes to read off the input stream when reading the body. HTTP 1.1 introduced the Transfer-Encoding header, which lets the client omit the Content-Length header, and instead create chunks of request body, which optimises the upload meaning that a) the server can start processing before it has everything, and b) more importantly for J2ME where memory might be a valuable resource, it lets the client send a bit of the request, free up that allocated memory and then send some more of the request. For a POST request, with no chunking, the headers and body might look like this: POST /log.jsp HTTP/1.1 User-Agent: Mozilla/4.0 (maxant J2ME Client) Accept: text/html,application/xhtml+xml,application/xml Content-Type: application/x-www-form-urlencoded Content-Length: 51 Host: wwwchaseamatecom:8089 problem=Failed%20to%20get%20installation%20response Chunked, that becomes: POST /ota/addInstallation.jsp HTTP/1.1 User-Agent: Mozilla/4.0 (maxant J2ME Client) Accept: text/html,application/xhtml+xml,application/xml Content-Type: application/x-www-form-urlencoded Host: wwwchaseamatecom:8089 Transfer-Encoding: chunked problem=Failed%20to%20get%20installation%20response You'll notice that the body of the second example, "problem=..." doesn't contain chunk headers (search Wikipedia for chunking to see an example). The reason is that I copied that text out of…
