playframework interview questions
Top playframework frequently asked interview questions
We are planning a project primarily serving content to mobile apps, but need to have a website.
My question is whether is makes sense to use Jersey or Restlet to develop REST APIs for our mobile apps, and then use Play! to serve the website.
Or does it make more sense to just use Play! to do it all? If so, how to do REST with Play! framework?
Source: (StackOverflow)
I'm new to Play framework. I'm trying to configure MySQL database as a datasource to be used with Play Ebeans.
Could you some one please explain the steps that are needed to configure MySQL with Play 2.0 framework (like, downloading drivers, adding dependency etc).
Source: (StackOverflow)
I was making my way through the Scala playframework tutorial and I came across this snippet of code which had me puzzled:
def newTask = Action { implicit request =>
taskForm.bindFromRequest.fold(
errors => BadRequest(views.html.index(Task.all(), errors)),
label => {
Task.create(label)
Redirect(routes.Application.tasks())
}
)
}
So i decided to investigate and came across this post.
I still don't get it.
Whats the difference between this:
implicit def double2Int(d : Double) : Int = d.toInt
and..
def double2IntNonImplicit(d : Double) : Int = d.toInt
other than the obvious fact they have different method names.
When should I use implicit and why?
Thanks in advance.
Source: (StackOverflow)
How can I change the default port used by the play framework in development mode when issueing the "run" command on the play console.
This is for playframework 2.0 beta.
Using the http.port configuration parameter either on the command line or in the application.conf seems to have no effect:
C:\dev\prototype\activiti-preso>play run --http.port=8080
[info] Loading project definition from C:\dev\prototype\activiti-preso\project
[info] Set current project to activiti-preso (in build file:/C:/dev/prototype/activiti-preso/)
Windows, really? Ok, disabling colors.
--- (Running the application from SBT, auto-reloading is enabled) ---
[error] org.jboss.netty.channel.ChannelException: Failed to bind to: 0.0.0.0/0.0.0.0:9000
[error] Use 'last' for the full log.
Source: (StackOverflow)
Using AngularJS with Scala Play, I'm getting this error.
Error: Argument 'MainCtrl' is not a function, got undefined
I'm trying to create a table consisting of the days of the week.
Please take a look at my code. I had checked the name of the Controller, but that seems correct. Note: Code used from this SO answer
index.scala.html
@(message: String)
@main("inTime") {
<!doctype html>
<html lang="en" ng-app>
<head>
<link rel="stylesheet" media="screen" rel='nofollow' href="@routes.Assets.at("stylesheets/main.css")">
</head>
<div ng-controller="MainCtrl">
<table border="1">
<tbody ng-repeat='(what,items) in data'>
<tr ng-repeat='item in items'>
<td ngm-if="$first" rowspan="{{items.length}}">{{what}}</td>
<td>{{item}}</td>
</tr>
</tbody>
</table>
</div>
</html>
}
MainCtrl.js
(function() {
angular.module('[myApp]', []).controller('MainCtrl', function($scope) {
$scope.data = {
Colors: ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"]
}
});
}());
Source: (StackOverflow)
Yet another LanguageX vs LanguageY question....
Currently I have a bunch of apps built on playframework. For the most part I love it. Moving from PHP a few years ago was almost a religious experience -- an actual functional orm, much less boiler plate code, stuff just worked, etc.
I still have a website running on a a shared hosting service thats built with PHP+CodeIgniter. Recently I've been adding some features to this site and have been thinking about porting it to either Ruby on Rails or Playframework.
So far though, nothing about rails has really blown me away. It seems like it has pretty much the same featureset as playframework. I like ruby's terseness, and things like blocks, but again for the most part there's been nothing about the language itself that has made me go "oh wow this is 1000x better than java/php/c/whatever!" In fact, some parts actually kind of rub me the wrong way -- I prefer strongly-typed languages for example.
My question is, am I likely to find anything in the framework or language that's really going to differentiate it from java+play for me, or are they pretty much the same and primarily just differentiated by things like personal preference about syntax and developer community?
Source: (StackOverflow)
Waaah, the Play! framework has so many static methods. Where I go to school, we were told never ever to use any statics, yet Play! uses it like there's no tomorrow. Is that somehow okay? If so, why?
We (7 people and I) are planning to use the Play! framework for a project involving a web app. We decided to do it with Play! because it looks quite fun to do, all of us already know Java and the assignment is pretty hard so we wanted to focus on the actual assignment rather than also learning how to program in a different language.
We were always told, however, NEVER EVER to use 'static's in any Java program we developed, but when I look at Play! ... Well... about half the methods are static. </exaggeration>
I suppose, at the very least, we could use singleton objects (by using Scala, for example ^^) in order to program our project, but I'm quite concerned at how many statics there actually are in framework itself.
So, should I be concerned about this? Did the way the Play! developers programmed it make it so that all these statics don't pose a problem?
(For example, this thread has a rant about why static members should be avoided at all costs.)
Source: (StackOverflow)
I am really torn between two different stacks with which to build a large application. One the one hand there is this option:
- Node.js
- express
- coffee script
- coffeekup
- mongoose/mongodb
or
- presistencejs/mysql
- Play Framework w/ Scala
- Anorm w/ mysql
- or mongodb
The node.js path is appealing to me because i can write all of the server side code, views and client side code in coffeescript, which i already know. If i go down this road i am still not 100% sure which db path i would take. mongoose makes storing data quick and easy, but the lack of true relationships might be more difficult to work with given the data model i have in mind (very SQLish).
The Play Framework path is also appealing because i know the framework well when using Java, but i don't know much about Scala, so there would be a hit to productivity as i work through learning that language. The Anorm database access layer is appealing because i can write the SQL by hand which i would prefer, and have the results mapped to objects automatically, which saves a lot of effort.
I keep leaning towards node.js, but i'm not sold on the best db access layer to use. Anyone have any experience with any of this and can share some insight?
Source: (StackOverflow)
We have a Play 1.2.4 application and we got Jenkins (on Ubuntu) for the application. We're having problems with Cobertura.
After running the tests (succesfully), every now and then, we get the following error:
---------------------------------------
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at net.sourceforge.cobertura.util.FileLocker.lock(FileLocker.java:124)
at play.modules.cobertura.CoberturaPlugin$CoberturaPluginShutdownThread.run(Unknown Source)
Caused by: java.nio.channels.OverlappingFileLockException
at sun.nio.ch.FileChannelImpl$SharedFileLockTable.checkList(FileChannelImpl.java:1166)
at sun.nio.ch.FileChannelImpl$SharedFileLockTable.add(FileChannelImpl.java:1068)
at sun.nio.ch.FileChannelImpl.lock(FileChannelImpl.java:824)
at java.nio.channels.FileChannel.lock(FileChannel.java:860)
... 6 more
---------------------------------------
Unable to get lock on /var/lib/jenkins/jobs/project/workspace/cobertura.ser.lock: null
This is known to happen on Linux kernel 2.6.20.
Make sure cobertura.jar is in the root classpath of the jvm
process running the instrumented code. If the instrumented code
is running in a web server, this means cobertura.jar should be in
the web server's lib directory.
Don't put multiple copies of cobertura.jar in different WEB-INF/lib directories.
Only one classloader should load cobertura. It should be the root classloader.
---------------------------------------
lock file could not be deleted
This doesn't seem to "break the build" but further down the build, we get the following (which causes the cobertura reports to fail)
Publishing Cobertura coverage report...
No coverage results were found using the pattern 'test-result/code-coverage/coverage.xml' relative to '/var/lib/jenkins/jobs/project/workspace'. Did you enter a pattern relative to the correct directory? Did you generate the XML report(s) for Cobertura?
Build step 'Publish Cobertura Coverage Report' changed build result to FAILURE
Running a subsequent build manually usually passes.
According to Zero code coverage with cobertura 1.9.2 but tests are working , I tried setting -Dcobertura.use.java.nio=false after play auto-test -command.
As this error was happening only now and then, I'm not totally sure if this helped. But after that, we got a problem with play auto-test hanging:
...
Executing /opt/play-1.2.4/play auto-test "/var/lib/jenkins/jobs/project/workspace" -Dcobertura.use.java.nio=false
[workspace] $ /opt/play-1.2.4/play auto-test "/var/lib/jenkins/jobs/project/workspace" -Dcobertura.use.java.nio=false
<build stuck here for a couple of days>
Since nothing has been totally deterministic, it's a bit difficult to say about causalities here. (This seems to happen after one or two builds after jenkins/server restart)
Currently I'm considering disabling Cobertura in our project, but if somebody has other ideas, that would be great =)
Source: (StackOverflow)
I'd like to know your experience finding a host for play applications on free or low-cost servers
So far now I found the following options:
Do you have any experience with one of these?
Any other option you know?
Source: (StackOverflow)
So I have successfully gotten ajax requests to work before but I have always had to use a form, and then at the end of the submit do return false so that it doesnt refresh the page.
I have also just recently moved my javascript into a seperate file this has caused my @ commands to fail. Because of this I do not no how to set my url to my route?
Html:
<button id="saveAsDefaultButton">Save as default</button>
Playframework java code:
public static Result saveDefaultPhoneForUser(String handset) {
User currentUser = User.findByName(session("name"));
currentUser.lastControlledHandset = theHandset;
currentUser.save();
return ok();
}
routes:
POST / controllers.Application.saveDefaultPhoneForUser(handset : String)
javascript:
$('#saveAsDefaultButton').click(function(evt) {
$('#errors').hide();
$.ajax({
type : 'POST',
url : "controllers.Application.saveDefaultPhoneForUser",
data : $('#controlledPhone option:selected').text(),
dataType : "text",
success : function(data) {
//setError('Call succedded');
//$('#test1').attr("src", data)
},
error : function(data) {
setError('Make call failed');
}
});
return false;
});
Im sure there is a way to do this I am just having no luck finding anything. Any help greatly appreaciated.
Source: (StackOverflow)
I am just getting started with Play Framework. I have downloaded and installed play and created a sample java application. When I try to start the play console in the application directory it hangs at "Loading project definition".
PS C:\dev\play\javatest> play.bat
Getting org.scala-sbt sbt_2.9.1 0.11.3 ...
:: retrieving :: org.scala-sbt#boot-app
confs: [default]
37 artifacts copied, 0 already retrieved (7245kB/283ms)
[info] Loading project definition from C:\dev\play\myFirstApp\project
When i try running a Scala application i get a message about it waiting for a lock:
PS C:\dev\play\scalatest> play
[info] Loading project definition from C:\dev\play\test1\project
Waiting for lock on C:\lib\play\repository\.sbt.ivy.lock to be available...
Running Windows 7, JDK 1.7.0_05 and Play Framework 2.0.2. Any ideas?
Source: (StackOverflow)
I am building a Java web app, using the Play! Framework. I'm hosting it on playapps.net. I have been puzzling for a while over the provided graphs of memory consumption. Here is a sample:
The graph comes from a period of consistent but nominal activity. I did nothing to trigger the falloff in memory, so I presume this occurred because the garbage collector ran as it has almost reached its allowable memory consumption.
My questions:
- Is it fair for me to assume that my application does not have a memory leak, as it appears that all the memory is correctly reclaimed by the garbage collector when it does run?
- (from the title) Why is java waiting until the last possible second to run the garbage collector? I am seeing significant performance degradation as the memory consumption grows to the top fourth of the graph.
- If my assertions above are correct, then how can I go about fixing this issue? The other posts I have read on SO seem opposed to calls to
System.gc(), ranging from neutral ("it's only a request to run GC, so the JVM may just ignore you") to outright opposed ("code that relies on System.gc() is fundamentally broken"). Or am I off base here, and I should be looking for defects in my own code that is causing this behavior and intermittent performance loss?
I apologize for the brain dump of questions; I've been debugging this issue for a while now, and would greatly appreciate any pointers.
UPDATE
I have opened a discussion on PlayApps.net pointing to this question and mentioning some of the points here; specifically @Affe's comment regarding the settings for a full GC being set very conservatively, and @G_H's comment about settings for the initial and max heap size.
Here's a link to the discussion, though you unfortunately need a playapps account to view it.
I will report the feedback here when I get it; thanks so much everyone for your answers, I've already learned a great deal from them!
Resolution
Playapps support, which is still great, didn't have many suggestions for me, their only thought being that if I was using the cache extensively this may be keeping objects alive longer than need be, but that isn't the case. I still learned a ton (woo hoo!), and I gave @Ryan Amos the green check as I took his suggestion of calling System.gc() every half day, which for now is working fine.
Thanks again for all the help, as always!
Source: (StackOverflow)
I want to add an object to the Global scope, and in order to construct it I need to pass it a path to a file.
I don't want to hard code the file path in the source, and so I want to get that path from the application.conf.
The problem is that I don't know how to access these properties from the java class.
I tried this:
Configuration.root().getString("file.path")
But it ends with a NullPointerException.
Am I wrong in assuming that there's a global Configuration instance that I can use?
Thanks.
Source: (StackOverflow)