Modern hardware systems have a multi-core architecture. So in contemporary software development concurrency is an even more crucial ingredient than before. But as we will see it is of great importance for single core systems, too. If you have already created a Java Swing application you’ve propably made an acquaintance with the SwingWorker, in order to delegate long running tasks from within Swing events to another thread. But first things first. In Swing the whole painting and event handling of the graphical user interface is executed in one thread the so called event dispatching-thread from AWT the underlying former window toolkit from Java. Therefore most of Swing-based methods are not thread-safe, meaning that you have to prevent race conditions by yourself, but it offers the possibility to dispatch tasks to the event-dispatcher thread. It is highly recommended to do everything, that updates the GUI in the corresponding thread.
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Category: Knowledge
Exception Handling for Injection Interceptor
Remember my post “Circular Injection of Util Classes in EJB 3.0“? There I offered a some kind of ugly solution to the circular dependency problem for managed classes in Java EE 5. In a preceding post (Circular Dependencies of Session Beans) I grumbled about the exception handling in jBoss-5.1. It lets you alone with a meaningless error message and you have to guess what the problem is. Unfortunately my own code presented in the former post is even worse, since it logs problems but ignores them. It wasn’t mentioned for productive use, but it was annoying to me, so here is a little tune up adding exception handling and readable error messages.
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Circumvent Nested Transaction Issues in Tapestry-5.x
Ajax component events may be wrapped in a transaction as I pointed out in “Transaction Handling for Ajax Components in Tapestry-5.x“. But on some occasions an Ajax component event is surrounded by a component event. So the code in the ControllerUtil of article “Transaction Handling in Tapestry5” will lead to ‘transaction already active’ problems, since we try to begin a transaction in the nested ajax component event although there is already an active transaction attached to the current thread. We can overcome this situation by checking, whether an active transaction is present and begin/commit/rollback a new transaction iff not. This behavior is similar to the default transaction attribute REQUIRED in Java EE.
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Concurrent conversion of SVG to formats like PNG, EPS or PDF
In this post I’ll show how to use the ExecutorService of the java.concurrent package, in order to start as many inkscape shells as processors available on the current machine and to distribute a whole bunch of conversion tasks wisely on the cores. On my quad core I got a speedup of about 3.5, which is really near to 4.
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Informative Exceptions with Java Proxies
Information is essential for reasonable exception handling. Unfortunately, it is not always affordable to write custom exceptions providing all necessary information, especially in test code, e.g. for selenium tests. So, here is an approach to weave informative exceptions into your [test] code.
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Circular Dependencies of Session Beans via Manual EJB Lookup
In my last two posts (Circular Dependencies of Session Beans and Circular injection of Util Classes in EJB 3.0) I wrote, that it is possible to have circular dependencies between session beans via interceptors and manual EJB lookup. In this post I will sketch out how.
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Circular Injection of Util Classes in EJB 3.0
In my last post Circular Dependencies of Session Beans I presented a method to use interceptors in session beans in order to inject beans. This works great until you want to add circular dependencies. Then you have to look up the beans by name and inject them into the bean. But this is kind of cumbersome. So, if it is possible, have a bean structure, which is topologically sortable and inject util classes having circular dependencies between each other. This post shows how to achieve the latter.
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Circular Dependencies of Session Beans
This post is about circular dependencies between session beans (ejb 3.0), which is ‘not possible’ without manual loading. The manual variant might be the solution of choice for you. Therefore, I will sketch it out later in this post. The first part of this post post is about a trial to achieve this with @EJB annotation only … which failed! But perhaps it will stop some of you to try it out (for nuts) and it’s a great bridge to a solution by a snatch enabling to have circular injection of ‘your own’ beans. I will show you the latter in my next post.
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Menus with Icons in Ubuntu Karmic++
With the update to karmic koala ubuntu reversed the color scheme of context menus. Before the foreground had been dark and the background bright. Now, guess what, it’s the other way around. With this change, the property for showing icons in context menus has been disabled, too. This is due to transparency problems. Unfortunately, programs like eclipse make extensive use of this feature. So, not having these icons anymore is more than annoying.
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Standalone Tomcat with jBoss (2nd Edition)
This tutorial desribes, how to install and configure a standalone Tomcat, so that a deployed webapp can connect to a jBoss and use the authentication of the application server. This method is decoupled from the login module or authentication type (LDAP, Database, …), respectively. It differs from the approach described in Standalone Tomcat with jBoss plus authentication against LDAP, in that it allows for parallel logged in users and it does not need to authenticate to LDAP/Database on both sides, but on the jBoss only.