I'm trying to port some code from Play Framework Java to Play Framework Scala but I'm having some issues with porting a tag.
The tag in question in the Java version checks the contents of the Flash scope and creates notifications to the user according to its values (error, success, etc).
I tried to create a Scala view (flag.scala.html):
#()(implicit flash:play.mvc.Scope.Flash)
#if(flash.get("error")) {
<p style="color:#c00">
#flash.get("error")
</p>
}
Which I call from main.scala.html via:
#views.Application.html.flag()
The error I get is:
The file {module:.}/tmp/generated/views.html.main.scala could not be
compiled. Error raised is : could not find implicit value for
parameter flash: play.mvc.Scope.Flash
The call to the new tag is correct, as if I replace the content by some String that's shown in the browser.
I'm sure it's something stupid but I got stuck. Any suggestion?
I don't know the details of Play, but this compile error is saying you should either:
Pass an explicit instance of play.mvc.Scope.Flash in the call to flag(),
views.Application.html.flag()(myFlash)
or
Make an implicit instance of Flash available in the scope where flag() is called. You could do this by importing the contents of some object (import some.path.FlashImplicits._) or by defining the implicit instance yourself,
implicit val myFlash: play.mvc.Scope.Flash = ...
...
views.Application.html.flag()
So the real question becomes: where do you want to get this Flash instance from?
You should not create an implementation for "implicit flash : Flash" on your own. Just add a "implicit request" to your action and it should work.
More details is here at the end of the page: https://github.com/playframework/Play20/wiki/ScalaSessionFlash
Ivan had the right suggestion, adding "implicit request". However, his link seems outdated. If you want a more explicit explanation, check out my answer to a similar question, here:
How to pass flash data from controller to view with Play! framework
I had the same issue but looking at the documentation i found the following:
If the error ‘could not find implicit value for parameter flash:
play.api.mvc.Flash’ is raised then this is because your Action didn’t
import a request object. Add an “implicit request=>”
of course the implicit Flash must appear in every view if you have nested views like:
#(implicit flash: Flash){
#main(){<h1>hello</h1>}
}
this view does not use flash scope but if main uses it, should be declared in views using main because the compiler will complain.
source: http://www.playframework.com/documentation/2.1.1/ScalaSessionFlash
Related
In a nutshell, if I define a constructor in a class thats named after the same name as the file itself, it returns the following area.
Some example code. Take the filename as ParseWebsiteData.scala for both.
This returns an error.
class ParseWebsiteData(url:String) {
}
This however, works fine.
class Foo(url:String) {
}
The only thing that I'm seeing as the issue are parser bugs from 2013, but this is the latest version of Eclipses's Scala IDE setup so I'm strongly thinking this is not the case, but turns out I'm wrong. Oops :(
As it's still an issue, what are the way(s) to avoid this occurring as I code in the future?
Well, can't tell the root cause but I was getting the same error in Scala Eclipse editor and I just did "project->clean" and it was gone!
Am facing an issue while trying to implement an example given over a website.
One of the methods in a class has a signature like this -
private void updateTable(JsArray prices) {....}
And am trying to invoke this method from another method as -
updateTable(JsonUtils.safeEval(response.getText()));
while doing this am seeing a compilation error as -
The method updateTable(JsArray) in the type StockWatcher is not applicable for the arguments (JavaScriptObject)
Though I have just used the exact code displayed in the website, am seeing this error. Not sure what needs to be done. Please help.
The problem has been fixed by making the following change -
updateTable((JsArray)JsonUtils.safeEval(response.getText()));
introduced a casting in the above statement.
I am using the Selenium dsl and would like to use a Page object. Currently however it seems I have to define the page object inside the test class. The reason I would want a page object is to share common features between tests so this seems a bit pointless... Has anyone been using the page object model with Selenium DSL? What is the idea behind defining the page object in the same class? How come I get a compiler error if I define the page object outside of the test class. Am I doing something wrong?
The compiler error I get is:
Expected MySpec.this.type#Page, actual: MyPage
You can define the class outside of the test class like this:
class TwitterPage {
val url = "http://twitter.com"
}
Then, use it inside the test by mixing in the Page trait:
val page = new TwitterPage with Page
go to page
title should be ("Welcome to Twitter")
This compiled and worked just fine for me.
Hi I am trying to learn JAVA deeply and so I am digging into the JDK source code in the following lines:
URL url = new URL("http://www.google.com");
URLConnection tmpConn = url.openConnection();
I attached the source code and set the breakpoint at the second line and stepped into the code. I can see the code flow is: URL.openConnection() -> sun.net.www.protocol.http.Handler.openConnection()
I have two questions about this
First In URL.openConnection() the code is:
public URLConnection openConnection() throws java.io.IOException {
return handler.openConnection(this);
}
handler is an object of URLStreamHandler, define as blow
transient URLStreamHandler handler;
But URLStreamHandler is a abstract class and method openConnection() is not implement in it so when handler calls this method, it should go to find a subclass who implement this method, right? But there are a lot classes who implement this methods in sun.net.www.protocol (like http.Hanlder, ftp.Handler ) How should the code know which "openConnection" method it should call? In this example, this handler.openConnection() will go into http.Handler and it is correct. (if I set the url as ftp://www.google.com, it will go into ftp.Handler) I cannot understand the mechanism.
second. I have attached the source code so I can step into the JDK and see the variables but for many classes like sun.net.www.protocol.http.Handler, there are not source code in src.zip. I googled this class and there is source code online I can get but why they did not put it (and many other classes) in the src.zip? Where can I find a comprehensive version of source code?
Thanks!
First the easy part:
... I googled this class and there is source code online I can get but why they did not put it (and many other classes) in the src.zip?
Two reasons:
In the old days when the Java code base was proprietary, this was treated as secret-ish ... and not included in the src.zip. When they relicensed Java 6 under the GPL, they didn't bother to change this. (Don't know why. Ask Oracle.)
Because any code in the sun.* tree is officially "an implementation detail subject to change without notice". If they provided the code directly, it helps customers to ignore that advice. That could lead to more friction / bad press when customer code breaks as a result on an unannounced change to sun.* code.
Where can I find a comprehensive version of source code?
You can find it in the OpenJDK 6 / 7 / 8 repositories and associated download bundles:
http://hg.openjdk.java.net/jdk6/jdk6 - http://download.java.net/openjdk/jdk6/
http://hg.openjdk.java.net/jdk7/jdk7 - http://download.java.net/openjdk/jdk7/
http://hg.openjdk.java.net/jdk8/jdk8
Now for the part about "learning Java deeply".
First, I think you are probably going about this learning in a "suboptimal" fashion. Rather than reading the Java class library, I think you should be reading books on java and design patterns and writing code for yourself.
To the specifics:
But URLStreamHandler is a abstract class and method openConnection() is not implement in it so when handler calls this method, it should go to find a subclass who implement this method, right?
At the point that the handler calls than method, it is calling it on an instance of the subclass. So finding the right method is handled by the JVM ... just like any other polymorphic dispatch.
The tricky part is how you got the instance of the sun.net.www.protocol.* handler class. And that happens something like this:
When a URL object is created, it calls getURLStreamHandler(protocol) to obtain a handler instance.
The code for this method looks to see if the handler instance for the protocol already exists and returns that if it does.
Otherwise, it sees if a protocol handler factory exists, and if it does it uses that to create the handler instance. (The protocol handler factory object can be set by an application.)
Otherwise, searches a configurable list of Java packages to find a class whose FQN is package + "." + protocol + "." + "Handler", loads it, and uses reflection to create an instance. (Configuration is via a System property.)
The reference to handler is stored in the URL's handler field, and the URL construction continues.
So, later on, when you call openConnection() on the URL object, the method uses the Handler instance that is specific to the protocol of the URL to create the connection object.
The purpose of this complicated process is to support URL connections for an open-ended set of protocols, to allow applications to provide handlers for new protocols, and to substitute their own handlers for existing protocols, both statically and dynamically. (And the code is more complicated than I've described above because it has to cope with multiple threads.)
This is making use of a number of design patterns (Caches, Adapters, Factory Objects, and so on) together with Java specific stuff such as the system properties and reflection. But if you haven't read about and understood those design patterns, etcetera, you are unlikely to recognize them, and as a result you are likely to find the code totally bamboozling. Hence my advice above: learn the basics first!!
Take a look at URL.java. openConnection uses the URLStreamHandler that was previously set in the URL object itself.
The constructor calls getURLStreamHandler, which generates a class name dynamically and loads, and the instantiates, the appropriate class with the class loader.
But URLStreamHandler is a abstract class and method openConnection()
is not implement in it so when handler calls this method, it should go
to find a subclass who implement this method, right?
It has to be declared or abstract or implemented in URLStreamHandler. If you then give an instance of a class that extends URLStreamHandler with type URLStreamHandler and call the openConnection() method, it will call the one you have overriden in the instance of the class that extends URLStreamHandler if any, if none it will try to call the one in URLStreamHandler if implemented and else it will probably throw an exception or something.
I am testing a parser I have written in Scala using ScalaTest. The parser handles one file at a time and it has a singleton object like following:
class Parser{...}
object Resolver {...}
The test case I have written is somewhat like this
describe("Syntax:") {
val dir = new File("tests\\syntax");
val files = dir.listFiles.filter(
f => """.*\.chalice$""".r.findFirstIn(f.getName).isDefined);
for(inputFile <- files) {
val parser = new Parser();
val c = Resolver.getClass.getConstructor();
c.setAccessible(true);
c.newInstance();
val iserror = errortest(inputFile)
val result = invokeparser(parser,inputFile.getAbsolutePath) //local method
it(inputFile.getName + (if (iserror)" ERR" else " NOERR") ){
if (!iserror) result should be (ResolverSuccess())
else if(result.isInstanceOf[ResolverError]) assert(true)
}
}
}
Now at each iteration the side effects of previous iterations inside the singleton object Resolver are not cleaned up.
Is there any way to specify to scalatest module to re-initialize the singleton objects?
Update: Using Daniel's suggestion, I have updated the code, also added more details.
Update: Apparently it is the Parser which is doing something fishy. At subsequent calls it doesn't discard the previous AST. strange. since this is off topic, I would dig more and probably use a separate thread for the discussion, thanks all for answering
Final Update: The issue was with a singleton object other than Resolver, it was in some other file so I had somehow missed it. I was able to solve this using Daniel Spiewak's reply. It is dirty way to do things but its also the only thing, given my circumstances and also given the fact I am writing a test code, which is not going into production use.
According to the language spec, no, there is no way to recreate singleton objects. However, it is possible to reflectively invoke the constructor of a singleton, which overwrites the internal MODULE$ field which contains the actual singleton value:
object Test
Test.hashCode // => e.g. 779942019
val c = Test.getClass.getConstructor()
c.setAccessible(true)
c.newInstance()
Test.hashCode // => e.g. 1806030550
Now that I've shared the evil secret with you, let me caution you never, ever to do this. I would try very very hard to adjust the code, rather than playing sneaky tricks like this one. However, if things are as you say, and you really do have no other option, this is at least something.
ScalaTest has several ways to let you reinitialize things between tests. However, this particular question is tough to answer without knowing more. The main question would be, what does it take to reinitialize the singleton object? If the singleton object can't be reinitialized without instantiating a new singleton object, then you'd need to make sure each test loaded the singleton object anew, which would require using custom class loaders. I find it hard to believe someone would design something that way, though. Can you update your question with more details like that? I'll take a look again later and see if the extra details makes the answer more obvious.
ScalaTest has a runpath that loads classes anew for each run, but not a testpath. So you'll have to roll your own. The real problem here is that someone has designed this in a way that it is not easily tested. I would look at loading Resolver and Parser with a URLClassLoader inside each test. That way you'd get a new Resolver each test.
You'll need to take Parser & Resolver off of the classpath and off of the runpath. Put them into a directory of their own. Then create a URLClassLoader for each test that points to that directory. Then call findClass("Parser") on that class loader to get it. I'm assuming Parser refers to Resolver, and in that case the JVM will go back to the class loader that loaded Parser to get Resolver, which is your URLClassLoader. Do a newInstance on the Parser to get the instance. That should solve your problem, because you'll get a new Resolver singleton object for each test.
No answer, but I do have a simple example of where you might want to reset the singleton object in order to test the singleton construction in multiple, potential situations. Consider something stupid like the following code. You may want to write tests that validates that an exception is thrown when the environment isn't setup correctly and also write a test validates that an exception does not occur when the environment is not setup correctly. I know, I know everyone says, "Provide a default when the environment isn't setup correctly." but I DO NOT want to do this; it would cause issues because there would be no notification that you're using the wrong system.
object RequiredProperties extends Enumeration {
type RequiredProperties = String
private def getRequiredEnvProp(propName: String) = {
sys.env.get(propName) match {
case None => throw new RuntimeException(s"$propName is required but not found in the environment.")
case Some(x) => x
}
}
val ENVIRONMENT: String = getRequiredEnvProp("ENVIRONMENT")
}
Usage:
Init(RequiredProperties.ENVIRONMENT)
If I provided a default then the user would never know that it wasn't set and defaulted to the dev environment. Or something along these lines.