Question

I’m working on a 1.2 Play! framework application, and I have a problem when deploying it as a WAR on a Tomcat 6.

One page of my application displays a list of information.
These information are retrieved from a .yml file.
So I have a controller that generate a Iterable<Object> from this .yml file, like that:

public static void myFunction() {
    Constructor constructor = new Constructor(MyClass.class); // org.yaml.snakeyaml.constructor.Constructor
    constructor.addTypeDescription(new TypeDescription(MyClass.class));
    Yaml yaml = new Yaml(constructor);
    Iterable<Object> listOfInfo = yaml.loadAll(Application.class.getResourceAsStream("/my-file.yml"));
    render("Application/my-page.html", listOfInfo);
}

The important point is that MyClass is located in the app/my/company/my-app/ package (my.company.my-app.MyClass).

When I run my application using play run, there is no problem.

Now, I build the WAR package (using play war -o some/dir --zip), and I install this generated WAR on a Tomcat (6.0).
Once the server is started, and try to access the corresponding page, I get the following error:

@683lh76fn
Internal Server Error (500)

Template execution error (In /app/views/Application/my-page.html around line 9)
Execution error occured in template /app/views/Application/my-page.html. Exception raised was ConstructorException : null; Can't construct a java object f
or tag:yaml.org,2002:my.company.my-app.MyClass; exception=Class not found: my.company.my-app.MyClass.

play.exceptions.TemplateExecutionException: null; Can't construct a java object for tag:yaml.org,2002:my.company.my-app.MyClass; exception
=Class not found: my.company.my-app.MyClass
        at play.templates.BaseTemplate.throwException(BaseTemplate.java:84)
        at play.templates.GroovyTemplate.internalRender(GroovyTemplate.java:252)
        at play.templates.Template.render(Template.java:26)
        at play.templates.GroovyTemplate.render(GroovyTemplate.java:184)
        at play.mvc.results.RenderTemplate.<init>(RenderTemplate.java:24)
        at play.mvc.Controller.renderTemplate(Controller.java:659)
        at play.mvc.Controller.renderTemplate(Controller.java:639)
        at play.mvc.Controller.render(Controller.java:694)
        at controllers.Application.myFunction(Application.java:311)

If I have a look in the exploded war, I see that my.company.my-app.MyClass is located in the directory WEB-INF/application/precompiled/java/my/company/my-app/ directory.

If I move this directory into WEB-INF/classes, then I don’t get this error anymore.

Why does this error occurs? What are my options to make it work (without modifying manually the WAR)?

Answer 1

I finally found the answer of this problem!

The Yaml parser (snakeyaml) creates its own ClassLoader in order to parse a .yml file. The structure of the Play! framework uses its own ClassLoader, and the compiled classes are located in the WEB-INF/application/precompiled/java directory, which is not the WAR standard.
Due to that, Yaml was not able to retrieve the classes, in particular MyClass.class.

The solution to solve this issue (except by modifying the WAR using Ant for example), is to give the Play! ClassLoader to the Yaml parser. Instead of writing that:

Constructor constructor = new Constructor(MyClass.class);
constructor.addTypeDescription(new TypeDescription(MyClass.class));

I write:

CustomClassLoaderConstructor constructor = new CustomClassLoaderConstructor(MyClass.class, MyController.class.getClassLoader());
constructor.addTypeDescription(new TypeDescription(MyClass.class));

using this, I can use the WAR created by Play! directly without getting the Yaml error anymore!