When trying to deploy app with context root "/" to JBoss AS 7 / EAP 6 in default configuration, you will encounter the following.

06:46:17,324 ERROR [org.jboss.msc.service.fail] (MSC service thread 1-1) MSC000001: Failed to start service jboss.web.deployment.default-host./ROOT: org.jboss.msc.service.StartException in service jboss.web.deployment.default-host./ROOT: Failed to start service
    at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1767) [jboss-msc-1.0.4.GA-redhat-1.jar:1.0.4.GA-redhat-1]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) [rt.jar:1.7.0_09-icedtea]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) [rt.jar:1.7.0_09-icedtea]
    at java.lang.Thread.run(Thread.java:722) [rt.jar:1.7.0_09-icedtea]
Caused by: java.lang.IllegalStateException: JBAS018038: Root contexts can not be deployed when the virtual host configuration has the welcome root enabled, disable it and redeploy
    at org.jboss.as.web.deployment.WebContextInjector.inject(WebContextInjector.java:57)
    at org.jboss.as.web.deployment.WebContextInjector.inject(WebContextInjector.java:38)
    at org.jboss.msc.inject.CastingInjector.inject(CastingInjector.java:55) [jboss-msc-1.0.4.GA-redhat-1.jar:1.0.4.GA-redhat-1]
    at org.jboss.msc.service.ServiceControllerImpl.doInject(ServiceControllerImpl.java:1549) [jboss-msc-1.0.4.GA-redhat-1.jar:1.0.4.GA-redhat-1]
    at org.jboss.msc.service.ServiceControllerImpl.access$1900(ServiceControllerImpl.java:49) [jboss-msc-1.0.4.GA-redhat-1.jar:1.0.4.GA-redhat-1]
    at org.jboss.msc.service.ServiceControllerImpl$StartTask.performInjections(ServiceControllerImpl.java:1780) [jboss-msc-1.0.4.GA-redhat-1.jar:1.0.4.GA-redhat-1]
    at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1741) [jboss-msc-1.0.4.GA-redhat-1.jar:1.0.4.GA-redhat-1]
    ... 3 more

This is because AS has the root context occupied by default welcome page.

BTW, I would suggest to switch that off automatically when deploying anything with root context ("/"), and switch it off when it's undeployed... anyway:

Solution

Though Management API or CLI:

For AS 7:

/profile=default/subsystem=web/virtual-server=default-host:write-attribute(name=enable-welcome-root,value=false)

For EAP 6.1:

/subsystem=web/virtual-server=default-host/:write-attribute(name=enable-welcome-root,value=false)

You should get:

{
    "outcome" => "success",
    "response-headers" => {
        "operation-requires-reload" => true,
        "process-state" => "reload-required"
    }
}

Alternative way, for both:

Shut down the AS and switch it to "false" in standalone.xml.

<subsystem xmlns="urn:jboss:domain:web:1.2" default-virtual-server="default-host" native="false">
    <virtual-server name="default-host" enable-welcome-root="false">
    ...

In case you have an older Java 6 application and want to switch to Java 7 code with goodies like diamond operator and multi-type exceptions:

touch .openshift/markers/java7
git add .openshift/markers/java7

Also make sure you don't have it ignored in .gitignore like I had.

Then in pom.xml

<plugin>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.0</version>
    <configuration>
        <source>1.7</source>
        <target>1.7</target>
    </configuration>
</plugin>

Then git push, and you're done.

My friends are writing a web app. Java EE 6 (JBoss EAP 6.0.1), JPA/Hibernate.

DTOs

On other colleague's advice, they don't use collections in Entities at all. Instead, they query for lists of entities and build up DTOs with collections, using multiple calls.

What do you think about this approach? Is it justifiable? Or is it rather about lack of experience with Hibernate?

I personally do mixed approach. I use @OneToMany collections whereever needed, even bi-di.

But I try to avoid @ManyToMany, and if there's need for it, I rather create an entity between, or don't map the other side.

Bottom-up

Also, since they don't have UI yet, they started creating the service / DAO layers.

They have kind of complete set of CRUDs for all entities.

But in my experience, this leads to a lot of unused code, and what they will really need when building UI won't be there.

Plus, there's a danger of view layer programmers won't ask for the right methods;

instead, they will use existing ones and code the rest in Java code, what will lead to a highly inefficient DB usage.

Isn't it better to start coding after you have at least some UI and use cases?