Andrej Koelewijn

Nexus is a maven repository manager. You can use Nexus to host your own maven repository for artifact created in your company, or for caching external artifacts.

Getting started with Nexus is pretty easy. Download the application. The package contains a webserver, so you don’t have to have a java container running. Simply unpack the downloaded archive and start the applications:

cd nexus/nexus-webapp-1.5.0/bin/jsw/linux-x86-32/
nexus start

Nexus has a web interface for managing your maven repository. The url for this web app is: http://localhost:8081/nexus/. The preconfigured admin account is admin, password: admin123.

According to the Nexus documentation you need to enable remote index downloads on a new installation, but it seems that this has been removed in the latest Nexus release. I couldn’t find the checkbox mentioned in Nexus 1.5.0.

Next you need to tell maven to use your maven repository. To do this, modify $HOME/.m2/settings.xml as follows:

<?xml version="1.0" encoding="UTF-8"?>
<settings xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">
  <mirrors>
    <mirror>
      <id>nexus</id>
      <mirrorOf>*</mirrorOf>
      <url>http://localhost:8081/nexus/content/groups/public</url>
    </mirror>
  </mirrors>
  <proxies></proxies>
  <servers></servers>
  <pluginGroups></pluginGroups>
  <profiles>
    <profile>
      <id>nexus</id>
      <!--Enable snapshots for the built in central repo to direct -->
      <!--all requests to nexus via the mirror -->
      <repositories>
        <repository>
          <id>central</id>
          <url>http://central</url>
          <releases><enabled>true</enabled></releases>
          <snapshots><enabled>true</enabled></snapshots>
        </repository>
      </repositories>
      <pluginRepositories>
        <pluginRepository>
          <id>central</id>
          <url>http://central</url>
          <releases><enabled>true</enabled></releases>
          <snapshots><enabled>true</enabled></snapshots>
        </pluginRepository>
      </pluginRepositories>
    </profile>
  </profiles>
  <activeProfiles>
    <activeProfile>nexus</activeProfile>
  </activeProfiles>
</settings>

To make sure you are actually using dependencies downloaded through nexus, delete all dependencies maven has already cached on your system:

rm -rf ~/.m2/repository

To test this Nexus setup, we can create a little java application using maven. The following create a java web application:

mvn archetype:create -DarchetypeGroupId=org.apache.maven.archetypes -DarchetypeArtifactId=maven-archetype-webapp -DgroupId=nl.iteye -DartifactId=App1
cd App1

You should now be able to compile and package your application:

mvn clean install

Next we’ll add the embedded glassfish maven plugin to our pom so we can test the web application. Add the plugin in the build section of your pom:

    <plugins>
         <plugin>
            <groupId>org.glassfish</groupId>
            <artifactId>maven-embedded-glassfish-plugin</artifactId>
            <version>3.0</version>
            <configuration>
               <app>${project.build.directory}/${build.finalName}.war</app>
               <port>7070</port>
               <containerType>web</containerType>
            </configuration>
         </plugin>
    </plugins>

When you try to run your application using the embedded glassfish plugin you’ll run into an error as maven will not be able to download all the required dependencies:

$:~/projects/jee/App1$ mvn embedded-glassfish:run
[INFO] Scanning for projects...
Downloading: http://localhost:8081/nexus/content/groups/public/org/glassfish/maven-embedded-glassfish-plugin/3.0/maven-embedded-glassfish-plugin-3.0.pom
[INFO] Unable to find resource 'org.glassfish:maven-embedded-glassfish-plugin:pom:3.0' in repository central (http://central)
Downloading: http://localhost:8081/nexus/content/groups/public/org/glassfish/maven-embedded-glassfish-plugin/3.0/maven-embedded-glassfish-plugin-3.0.pom
[INFO] Unable to find resource 'org.glassfish:maven-embedded-glassfish-plugin:pom:3.0' in repository central (http://central)
[INFO] ------------------------------------------------------------------------
[ERROR] BUILD ERROR
[INFO] ------------------------------------------------------------------------
[INFO] Error building POM (may not be this project's POM).

Project ID: org.glassfish:maven-embedded-glassfish-plugin

Reason: POM 'org.glassfish:maven-embedded-glassfish-plugin' not found in repository: Unable to download the artifact from any repository

  org.glassfish:maven-embedded-glassfish-plugin:pom:3.0

from the specified remote repositories:
  nexus (http://localhost:8081/nexus/content/groups/public)

 for project org.glassfish:maven-embedded-glassfish-plugin

To fix this problem we need to add the maven repository containing the glassfish plugin to Nexus. Log into Nexus using the admin account and, select repositories,and then add a proxy repository. Specify the following repository:

Next we need to add the glassfish proxy repository to the Public Repositories group:

Move the Glassfish Maven 2 Repository from available repositories to ordered group repositories:

Now you should be able to start Glassfish using maven, as Nexus will be able to find the required dependencies:

$:~/projects/jee/App1$ mvn embedded-glassfish:run
[INFO] Scanning for projects...
Downloading: http://localhost:8081/nexus/content/groups/public/org/glassfish/maven-embedded-glassfish-plugin/3.0/maven-embedded-glassfish-plugin-3.0.pom
4K downloaded  (maven-embedded-glassfish-plugin-3.0.pom)
[WARNING] *** CHECKSUM FAILED - Checksum failed on download: local = '7e111e395ec93ac48034fdf599552d547dc27618'; remote = '085185fbf2f1b3d0d36e557f4d42c9f47edc4d2c' - RETRYING
Downloading: http://localhost:8081/nexus/content/groups/public/org/glassfish/maven-embedded-glassfish-plugin/3.0/maven-embedded-glassfish-plugin-3.0.pom
4K downloaded  (maven-embedded-glassfish-plugin-3.0.pom)
[WARNING] *** CHECKSUM FAILED - Checksum failed on download: local = '7e111e395ec93ac48034fdf599552d547dc27618'; remote = '085185fbf2f1b3d0d36e557f4d42c9f47edc4d2c' - IGNORING
Downloading: http://localhost:8081/nexus/content/groups/public/org/glassfish/maven-embedded-glassfish-plugin/3.0/maven-embedded-glassfish-plugin-3.0.jar
16K downloaded  (maven-embedded-glassfish-plugin-3.0.jar)
[WARNING] *** CHECKSUM FAILED - Checksum failed on download: local = 'd6e53dbbc063ccb40aa673f0a56bafa0c2c225db'; remote = '0469be7e503a1c3df4c8ddf199b1fba3a998cca2' - RETRYING
Downloading: http://localhost:8081/nexus/content/groups/public/org/glassfish/maven-embedded-glassfish-plugin/3.0/maven-embedded-glassfish-plugin-3.0.jar
16K downloaded  (maven-embedded-glassfish-plugin-3.0.jar)
[WARNING] *** CHECKSUM FAILED - Checksum failed on download: local = 'd6e53dbbc063ccb40aa673f0a56bafa0c2c225db'; remote = '0469be7e503a1c3df4c8ddf199b1fba3a998cca2' - IGNORING
[INFO] ------------------------------------------------------------------------
[INFO] Building App1 Maven Webapp
[INFO]    task-segment: [embedded-glassfish:run]
[INFO] ------------------------------------------------------------------------
Downloading: http://localhost:8081/nexus/content/groups/public/org/glassfish/extras/glassfish-embedded-all/3.0/glassfish-embedded-all-3.0.pom
10K downloaded  (glassfish-embedded-all-3.0.pom)
Downloading: http://localhost:8081/nexus/content/groups/public/org/glassfish/extras/extras/3.0/extras-3.0.pom
2K downloaded  (extras-3.0.pom)
Downloading: http://localhost:8081/nexus/content/groups/public/org/glassfish/glassfish-parent/3.0/glassfish-parent-3.0.pom
53K downloaded  (glassfish-parent-3.0.pom)
...
INFO: Security service(s) started successfully....
classLoader = WebappClassLoader (delegate=true; repositories=WEB-INF/classes/)
SharedSecrets.getJavaNetAccess()=java.net.URLClassLoader$7@181c4eb
Mar 9, 2010 9:34:51 PM com.sun.enterprise.web.WebApplication start
INFO: Loading application App1 at /App1
Hit ENTER to redeploy, X to exit

That’s about it.

If you are just starting out with JEE CDI (Weld), it’s easy to forget the required beans.xml file. If you don’t include it, you may run into problems like this:

SEVERE: javax.el.PropertyNotFoundException: /index.xhtml @8,67 action="#{crm.ping}": Target Unreachable, identifier 'crm' resolved to null
javax.faces.el.EvaluationException: javax.el.PropertyNotFoundException: /index.xhtml @8,67 action="#{crm.ping}": Target Unreachable, identifier 'crm' resolved to null
	at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:95)
	at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102)
	at javax.faces.component.UICommand.broadcast(UICommand.java:315)
...

The beans.xml file (in META-INF/classes or WEB-INF/) can be empty or contain the following:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://java.sun.com/xml/ns/javaee"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://java.sun.com/xml/ns/javaee  http://java.sun.com/xml/ns/javaee/beans_1_0.xsd">
</beans>

I ran into the following problem yesterday while building a rest service using resteasy: the code would compile ok, but the unit tests wouldn’t run. I got the following exception in the output of the unit tests:

java.lang.ClassFormatError: Absent Code attribute in method that is not native or abstract in class file javax/ws/rs/ext/RuntimeDelegate
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(ClassLoader.java:621)
	at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)

The problem is caused by the javeee-api dependency in my maven pom. As described here, the following dependency provides you with the java-ee api’s, not the implementation. This is ok for compiling, but can’t be used for executing code.

<dependency>
  <groupId>javax</groupId>
  <artifactId>javaee-api</artifactId>
  <version>6.0</version>
</dependency>

I thought i’d solved the issue by adding a scope of provided or even compile, but this doesn’t fix the problem. The maven build still fails with the Absent code attribute… error. Removing the dependency completely solves the issue for now, but will probably give me some problems when i add more code which uses jee6.

I tried Prezi yesterday, and looked at some of the presentations others made with it. It’s a nice idea, but absolutely not the presentation tool i’m looking for. Prezi basically is a mind-mapping tool, with some nice transitions. But mindmaps are for brainstorming your presentation content. You do not create a compelling presentation by showing a mindmap.

Slides need to be visual support for your story. It should be about visual storytelling. A presentation needs to be more like a live spoken documentary on Discovery channel or National Geographic Channel. I want to be able to create a movie with a presentation tool, not embed a movie. After you create the mindmap of your contents, you need to visualize it. This is where prezi falls short.

In my opinion it should offer a way to translate your mindmap into a storyboard. I really want a presentation tool which allows me to sketch out all the slides on a storyboard using a Wacom tablet. After you’ve created the storyboard, you need to fill the slides with all the real images and graphics. This means the software should have a lot of support for creating (vector) images, and adding photo’s. Integrated internet image search would be perfect. This means it needs to be a combination of animation software with onion skinning support, e.g. Pencil, vector graphics, e.g. Adobe Illustrator or Inkscape, and something like flickr search tool compflight.

It’s amazing how many people complain about the hardware specs, but forget about the software. The iPad has the most important feature of all: usability.

Remember mobile internet before the iPhone? Nobody used it. Then along came the iPhone: technically nothing new: touch screens existed before, mobile browsers existed before.

But only the usability of the iPhone has made people start to use mobile internet. So much so that AT&T has a hard time keeping up.

Hardware features don’t matter if the usability isn’t there. And that’s where the iPad shines, just look at some of the video’s here: New Multi-touch Interactions on the Apple iPad. Again, it’s all about the software. Software is the key to ease of use. Apple has just made computing a lot easier.

The video on the iPad page more or less proofs it’s purpuse: it’s THE couch device. Even the basic version seems good enough for most purposes: internet surfing, watching video, reading books and magazines, looking at your pictures.

I bet soon every member of your family will have his or her own iPad: we want to simultaneously watch a video, read a book, play a game. And with the keyboard dock, the tablet will replace laptops and desktops for many people.

Surprisingly it doesn’t seem to have a camera, which means it won’t be the ultimate ichat device. But i’m sure a future version will come with a camera, just another reason to upgrade to a newer version at some point.

It’ll be interesting to see what other hardware manufacturers are going to come up with to compete with the iPad. Problem for the competition is that software is such a big part of the iPad, it’s not just about the hardware.

Newspapers are looking to the ipad/islate/itablet to save their business, assuming that they can just copy their paper business to the tablet. Sell editions or subscription so customers can read their newspaper on the tablet.

However, every new technology starts with copying existing concepts. Initially on the web we saw copies of concepts that already existed: web shops, web magazines, web newspapers, web encyclopedia’s. But after a while people discover that the new technology has more to offer than a better/faster/easier way to do old concepts. It adds a whole range of new possibilities. The internet enables you to collect the knowledge of your visitors and customers to your product. Your visitors enable you to improve or completely create your products and service.

Similarly, tablet applications will initially resemble concepts we currently know which would work better on a tablet: books, newspapers, magazines. But tablets will bring their own wave of innovations. Newspaper can’t expect to just be a digital version of their current newspapers. They too will have to evolve and use these innovations, otherwise they will be surpassed by better solutions.

I have written before about what i think initial innovation on tablets will look like: media convergence. This will shake up all existing media companies.

It will also enable interactivity with these media. One of the most interesting ways to add interactivity is by adding gaming. Gaming enables better learning, working for free, and audience feedback. I think tablets will have a big impact on gaming as part of other media. Currently most of these media forms don’t allow user participation. This will change big time when tv, books, magazines and newspapers all converge on tablets.

The internet and web has created some expectations around media that media consumers are probably going to expect from media made available on a tablet:

• Findability – Using Google we can now find most content on the internet. How findable is your content in the app-store? Are we going to accept content that isn’t findable using a generic search engine?
• Aggregation – Feeds have made it easy to follow multiple websites. No need to visit all sites to find new articles. News is a lot easier to follow using feed readers. Some say this has become less important since twitter, but for twitter to work you need something else:
• Deeplinking – People like to directly link to interesting information on the internet. Can you send friends a link to a specific page? Can you send a link to a specific book in amazon, a video in youtube, a house on some real-estate site? Currently you can, but can you do this when everything becomes an iphone-app like closed application?
• Picking the interesting parts – Consumers currently expect to be able to just pay for the music or video that they like, without having to buy other stuff. Bundling popular information with less popular information like is done with magazines or music albums is less and less accepted.

Even if media offer their content on the tablet, consumers will have different expectations than they have with the old distribution format. Can media evolve and fullfill these expectations?

It’s funny to see that for some companies it’s not really clear who their customers are: are readers the customers of newspapers, and are newspapers providing them a services by selling them news? Or are advertisers the customers and are newspapers in the business of selling attention to the advertisers?

Both can work, but it seems to me that currently too much discussion on the internet is about convincing companies that one approach is working and the other not. Companies should treat readers as customers, or they should views them as a product to sell. People are trying to convince others that they should target different customers.

I think it’s more important to understand your model: if you know who your customer is, you can actually understand the value of what you’re trying to sell. Are you selling valuable news or are you selling commodity news? Or are you selling specific readers, or are you selling a large group of unfocused readers? Are there many other providers of the same service or is your service very special?

The basic economic demand and supply rules still apply. The value of scarce news is very high, the value of commodity news is very low. The value of targetted, focussed readers is very high, the value of unfocused readers is a bit lower.

Most people think good usability is not very important for internal IT systems: you can train the users and write manuals to compensate for bad usability. Also, your internal users have no choice, so they’re not going to go to the competition if your IT system is hard to use.

A story in webwereld shows that this is not true: Politie: onze statistieken zijn onbetrouwbaar. The dutch police are complaining that their statistics are incorrect: they don’t know what is happening, because their employees don’t enter the data. The new system is too hard to use, so employees refuse to use it.

Developers and techies often think that it’s enough for a product to have a specific functionality. That it doesn’t matter if it’s easy to use or not. For example, when a company like Apple launches a new product they’ll go: “that’s not new, some other product had that functionality long ago”. But there’s a huge difference between having a functionality, and making it easy enough so that users will actually start using it. Nice example is branching in version control systems: Subversion has had this ability forever, but Git makes it so easy that people actually start using it.

Moral of the story: usability isn’t just important when it’s a customer facing system, internal applications also need to be user friendly.

Use the following to configure git to use diffmerge for diffing and merging files:

git config --global diff.tool diffmerge
git config --global difftool.diffmerge.cmd "diffmerge \"\$LOCAL\" \"\$REMOTE\""

git config --global merge.tool diffmerge
git config --global mergetool.diffmerge.cmd diffmerge --merge --result=\"\$MERGED\"
  \"\$LOCAL\" \"\$BASE\" \"\$REMOTE\"
git config --global mergetool.diffmerge.trustexitcode false

The following will show diffmerge with the two versions of myfile.java side by side:

git difftool master~2 myfile.java