jBPM 4.3 and Spring

jBPM has just been released in version 4.3 and the spring integration has been changed. If you used to have an application that uses the spring integration of previous versions of jBPM, this might lead to exceptions like this:

org.springframework.beans.factory.BeanCurrentlyInCreationException:
Error creating bean with name 'repositoryService': Requested bean
is currently in creation: Is there an unresolvable circular
reference?

The problem is that rather than having to declare all of jBPM’s services in your application context — like it used to be up to jBPM 4.2 —, the new spring integration provides access to them through the Process Engine. All you need in your application context is this:

<bean id="springHelper">
  <property name="jbpmCfg" value="PATH TO YOUR jbpm.cfg.xml">
</property>
</bean>
<bean id="processEngine" factory-bean="springHelper"
factory-method="createProcessEngine" />

Now you can inject the processEngine into your classes and retrieve jBPM’s services like this:

processEngine.getExecutionService() …
processEngine.getRepositoryService() …
…

Tags: code, java, jBPM4
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Eclipse on Snow Leopard (10.6.2)

When I downloaded and installed Eclipse (eclipse-SDK-3.5.1-macosx-carbon.tar.gz) yesterday, I started to get the following error message:

Eclipse error message: "Cannot complete the request. This installation has not been configured properly for software updates!"

To fix this, you need to go to “Preferences > General > Capabilities” and check “Classic Update”. Afterwards you should be able to select “Help > Software Updates > Find and Install…”.

I wasn’t able to find much on the internet, but this post on an Ubuntu forum finally brought the solution.

Tags: eclipse, java, OS X
Posted in OS X, java | 2 Comments »

Maven Dependency Conflicts

Have you ever seen an exception like this:

org.springframework.beans.factory.BeanCreationException: Error
creating bean with name 'XY' defined in class path resource
[applicationContext.xml]: Instantiation of bean failed; nested
exception is org.springframework.beans.
BeanInstantiationException: Could not instantiate bean class
[XY]: Constructor threw exception; nested exception is
java.lang.LinkageError: You are trying to run JAXB 2.0 runtime
(from jar:file:/.../WEB-INF/lib/jaxb-impl-2.1.8.jar!/com/sun/
xml/bind/v2/model/impl/ModelBuilder.class)but you have old
JAXB 1.0 runtime earlier in the classpath (at jar:file:
/.../WEB-INF/lib/jaxb-impl-1.0.4.jar!/com/sun/xml/bind/
WhiteSpaceProcessor.class) Please remove the JAXB 1.0
runtime for 2.0 runtime to work correctly.

Well, I have, several times… and the task of having to figure out which library causes this dependency conflict seemed unresolvable pretty scary at first! Luckily, there is the m2eclipse plug-in with its excellent dependency graph. So if you are using Eclipse, whether you are actually using m2eclipse to manage your project or not, just the dependency graph makes it worth having a look at it. I still run my maven tasks on the command line, but have m2eclipse installed, just to be able to use the graph.

After identifying which library is causing the dependency conflict, all you have to do is to add an “exclude” node to that dependency in your pom.xml. In the above case, this snipped did the trick:

<dependency>
    <groupId>...</groupId>
    <artifactId>...</artifactId>
    <version>...</version>
    <exclusions>
        <exclusion>
            <artifactId>jaxb-impl</artifactId>
            <groupId>javax.xml</groupId>
        </exclusion>
        ...
    </exclusions>
</dependency>

Tags: code, development, java, maven, mvn
Posted in Frameworks, java | No Comments »

Java and Snow Leopard

I noticed that there isn’t a whole lot of useful information about Java and Snow Leopard (OS X 10.6) out there on the web. Maybe this is because there isn’t a whole lot to say about it. Snow Leopard comes with Java 6 (1.6.0_15 that is) only, which means that the links that still exist in the

/System/Library/Frameworks/JavaVM.framework/Versions/

directory all point to “CurrentJDK”, which points to “1.6″. The thing is that Snow Leopard ships with a 32 bit version and a 64 bit version of the VM (Virtual Machine), 64 bit being the default one. The Java Preferences app shows this nicely:

And that is the big news about it, since a 32 bit version of java 6 didn’t previously exist for OS X.

Now I’ve previously had to tweak Eclipse to use the 1.5 VM (see “Java Versions on Mac OS X“), and now it just works. I’m assuming that this is because of the “mixed mode”:

$ java -version
java version "1.6.0_15"
Java(TM) SE Runtime Environment (build 1.6.0_15-b03-219)
Java HotSpot(TM) 64-Bit Server VM (build 14.1-b02-90, mixed mode)

…so the VM would automatically detect if an application should be executed in 64 or 32 bit mode and then start the correct VM. I still need to investigate how this actually works. Anyway, the good news is that java and eclipse seems to be working better with Snow Leopard. I’ll write more on this as I continue working with it, for now here is an interesting post on the topic:

http://blog.zvikico.com/2009/09/eclipse-java-and-snow-leopard.html

Tags: code, java, OS X
Posted in OS X, java | 1 Comment »

Different Maven Versions on OS X

I keep running into the problem that different projects I’m working on require different versions of maven. I have two versions installed, maven 2.0.6 in /usr/share/maven-2.0.6 and maven 2.0.9 in /usr/share/maven. To find out which version of maven you are running, open a terminal and type the following

$ mvn --version
Maven version: 2.0.9
Java version: 1.6.0_07
OS name: "mac os x" version: "10.5.6" arch: "x86_64" Family: "mac"

In this case, maven 2.0.9 is running, so we’ll see how to switch to maven 2.0.6. First we need to know where the maven executable, or in this case, the symbolic link to the executable is located:

$ which mvn
/usr/bin/mvn

Next, we’ll use ls to check where the symbolic link is pointing:

$ ls -l /usr/bin/mvn
lrwxr-xr-x  1 root  wheel  24 Apr 24 14:26 /usr/bin/mvn -> /usr/share/maven/bin/mvn

Finally, if you have different maven versions installed, you can switch between them by overwriting the symbolic link:

$ sudo ln -fhsv /usr/share/maven-2.0.6/bin/mvn /usr/bin/mvn

After providing your password, the symbolic link should now be pointing to the maven 2.0.6 executable. To doublecheck, type

$ mvn --version

The output should be something like this

Maven version: 2.0.6

Tags: code, development, java, maven, OS X
Posted in OS X, java | No Comments »

Java Versions on Mac OS X

Update: This post refers to OS X 10.5 “Leopard”, if you are using 10.6 “Snow Leopard”, you might want to consider reading my post “Java and Snow Leopard” instead.

I just started using my Mac as a development machine and thought I’d share some of the issues and solutions I came across. I’m using Java 6, Tomcat 6, Eclipse 3.3.2 (Europa), hibernate 3, Spring 2.0.3 and tapestry 1.4.5.

The first issue I came across was an

UnsupportedClassVersionError: Bad version number in .class file

error when I tried to start tomcat. (I’m using the sysdeo plug-in to control tomcat, even though I’m aware that WTP is much better… I have my reasons, but that’s beyond the scope of this post.)

Now the title of the console in Eclipse revealed the problem, the Sysdeo plug-in was using version 1.4 of the Java RE. The thing is, I didn’t notice this until I tried a whole bunch of other stuff… which cost me quite a bit of time, but also helped understand a few things better.

OS X keeps the different Java versions neatly separated in the

/System/Library/Frameworks/JavaVM.framework/Versions

directory. By creating or overwriting the symbolic link “CurrentJDK”, you can change the default JDK version of your system. To do this, you have to change to the Versions directory and set a new symlink with ln:

$cd /System/Library/Frameworks/JavaVM.framework/Versions
$sudo ln -fhsv 1.6 CurrentJDK

After providing the administrator password, the default JDK will be set to version 1.6. Unfortunately, after doing this, I couldn’t start Eclipse anymore. The fix for this is to edit the following file:

/Applications/eclipse/Eclipse.app/Contents/Info.plist

and un-comment the following line:

<string>-vm</string><string>/System/Library/Frameworks/
JavaVM.framework/Versions/1.5.0/Commands/java</string>

This tells Eclipse to use a specific Java version, instead of the platforms default one. Now I was able to start Eclipse again and tomcat started without exceptions when I manually deployed my war files. My next step was to try Sysdeo to start Tomcat, which is where I realized that all I would have had to do was to set the correct JVM in Preferences > Tomcat > JVM Settings. Anyway, learned something on the way

Here are some links that helped me:

http://blog.kischuk.com/2008/05/08/running-eclipse-on-macbooks-with-java-6/

http://www.insanelymac.com/forum/index.php?showtopic=58817&st=0&p=435204&#entry435204

http://johnnywey.wordpress.com/2008/06/21/os-x-and-java-unsupportedclassversionerror/

Tags: java, OS X
Posted in OS X, java | 1 Comment »

Overview of reliable open source frameworks

In a Time of Less, Do More with Open Source: Top 25 Open Source Projects That Will Help Trim Development Budgets

Palamida published a useful list of reliable open source frameworks on their blog. There are no surprises on the list but they put it in relation to the person years it took to create these frameworks. Interesting!

Tags: code, development, framework, java
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“JAX-RS: The Java API for RESTful Web Services” Talk at Devoxx08

This talk was given by Paul Sandoz. He showed a few examples and listed the following existing implementations of JSR 311 (JAX-RS):

• Jboss RESTEasy
• Apache CXF
• Jersey. (Reference Impl.)
• Restlet
• Triaxrs

He was testing the services on a command line with curl (i.e. curl -v -d x=1 -H “Accept: application/xml” http://localhost:8080/xyz or “Accept: application/json”).

The JAX-RS Overview is supposed to be a good starting point to implement RESTful web services. His presentation and a zip file wih examples can be downloaded from his blog.

Tags: Devoxx, java, JAX-RS, REST, web services
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“Easy Entity Versioning with Envers” Talk at Devoxx08

This talk was given by Adam Warski. He is the creator of Envers, a framework that provides entity versioning for hibernate. It does this by creating additional auditing tables and inserting data to them on update/insert and delete. This creates global revisions, similar to the way it is done in Subversion. In order to activate versioning for a class, the @Versioned annotation is used. User information is not automatically stored with the revisions but can be added by implementing a custom RevisionListener.

Envers is now a hibernate core module and will be included in the next release of hibernate.

Here is a link to the current version of Envers

Tags: Devoxx, hibernate, java, persistence, versioning
Posted in Devoxx | No Comments »

JavaRebel

Just came across this at Devoxx: JavaRebel – like JVM HotSwap but without all the limitations. And I got a 90 day free license card… Nice!

Tags: Devoxx, hot swap, java, jvm
Posted in Devoxx | No Comments »