I'm trying to understand how CQ form components works.
I see that they use a variable called 'resource' a lot. For example, in the beginning of every componenet it always goes:
final String name = FormsHelper.getParameterName(resource);
final String id = FormsHelper.getFieldId(slingRequest, resource);
final boolean required = FormsHelper.isRequired(resource);
I know that Sling treats everything as a resource. But what exactly is this specific piece of 'resource'? Where is it defined? Where does it come from? And what does it contain?
The resource variable, which is an implementation of org.apache.sling.api.resource.Resource, is an object that represents a node entity in the jcr repository, but comes with some additional convenience methods compared to e.g. lower level javax.jcr.Node object.
In this case the mentioned resource likely represents the component's resource.
To explain why sling is using the terminology Resource:
A resource is a fundamental concept in restful APIs.
Resources are typed objects with associated data, relationships to other resources and methods that operate on it.
Sling is actually a restful layer on top of a Java Content Repository.
For the sling layer the repository is a virtual tree of resources.
I highly recommend you to read the official documentation for more details on this topic https://sling.apache.org/documentation/the-sling-engine/resources.html
Related
It is straightforward to put resource id into url if it is a int or long type. e.g.
GET files/123
But my problem is that my resource identifier is a path. e.g. /folder_1/folder_2/a.sh because the underlying implementation is a filesystem. So I can not put it as part of rest api url because it is conflict with url path.
Here's approaches what I can think of:
Put the path id as the request param. e.g.
GET files?path=/folder_1/folder_2/a.sh
Encode/decode the path to make it qualifier as part of url.
Introduce another int/long id for this resource in backend. And map it to the path. The int/long type resource id is stored in database. And I need to maintain the mapping for each CURD operation.
I am not sure whether approach 1 is restful, approach 2 needs extra encoding/decoding, and approach 3 needs extra work to maintain the mapping.
I wonder what is the best practice to design the rest api url for this kind of case.
Simple:
#GET
#Path("/files/{path:.+}")
#Produces({MediaType.TEXT_PLAIN})
public String files(
#PathParam("path") String path
) {
return path;
}
When you query files/test1/tes2 via url output is:
test1/tes2
Just put the path after a prefix, for example:
GET /files/folder_1/folder_2/a.sh
There isn't a conflict, since when the request path starts with your known prefix (/files/, in the above example), you know that the rest should be parsed as the path to the file, including any slashes.
Well, my experience designing "restful" APIs shows that you have to take into consideration future extensions of your API.
So, the guidelines work best when followed closely when it makes sense.
In your specific example, the path of the file is more of an attribute of the file, that can also serve as its unique ID.
From your API client's perspective, /files/123 would make perfect sense, but /files/dir1/file2.txt is debatable.
A query parameter here would probably help more, much like what you would do if you wanted to retrieve a filtered list of files, rather than the whole collection.
On the other hand, using a query parameter would also help for future extensions, since supporting /files/{path} would also mean conflicts when attempting to add sub-resources to your files endpoint.
For example, let's assume that you might need in the future another endpoint /files/attributes. But, having such an endpoint, would exclude any possibility for your clients to match a file named attributes.
I have configured my EF context configured like so
b.RegisterAssemblyTypes(webAssembly, coreAssembly)
.Where(t => t.IsAssignableTo<DbContext>())
.InstancePerLifetimeScope();
I would like to use it from a custom authorization attribute that hits the database using my EF context. This means no constructor-injection. I achieve this by using CommonSeviceLocator
var csl = new AutofacServiceLocator(container);
ServiceLocator.SetLocatorProvider(() => csl);
...
var user = await ServiceLocator.Current
.GetInstance<SiteContext>().FindAsync(id);
I am finding that this fails with a "multiple connections not supported" error if the browser issues two simultaneous requests to routes using this attribute. It seems like this might be due to what is mentioned in this answer. My guess is that ServiceLocator resolves from the root scope rather than the web request scope and the two request are conflicting (either request in isolation works fine).
This seems confirmed by that when I change to InstancePerRequest() I get this from any invocation of the attribute.
Autofac.Core.DependencyResolutionException No scope with a Tag matching 'AutofacWebRequest' is visible from the scope in which the instance was requested. This generally indicates that a component registered as per-HTTP request is
being requested by a SingleInstance() component (or a similar scenario.) Under the web integration always request dependencies from the DependencyResolver.Current or ILifetimeScopeProvider.RequestLifetime, never from the container itself.
So it seems like maybe ServiceLocator is simply not the way to go.
How do I resolve the request-scoped SiteContext from inside the attribute (using a service-locator pattern)?
Your issue derives from the fact that you are trying to put behavior inside of an Attribute. Attributes are for defining meta-data on code elements and assemblies, not for behavior.
Microsoft's marketing of Action Filter Attributes has led people implementing DI down the wrong path by putting both the Filter and the Attribute into the same class. As described in the post passive attributes, the solution is to break apart filter attributes into 2 classes:
An attribute that contains no behavior to mark code elements with meta-data.
A globally-registered filter that scans for the attribute and executes the desired behavior if present.
See the following for more examples:
Constructor Dependency Injection WebApi Attributes
Unity Inject dependencies into MVC filter class with parameters
Implementing passive attributes with dependencies that should be resolved by a DI container
Dependency Injection in Attributes: don’t do it!
Injecting dependencies into ASP.NET MVC 3 action filters. What's wrong with this approach?
How can I test for the presence of an Action Filter with constructor arguments?
Another option is to use IFilterProvider to resolve the filters as in IFilterProvider and separation of concerns.
Once you get your head around the fact that Attributes should not be doing anything themselves, using them with DI is rather straightforward.
For REST service is it a best practice to accept the complete Request as input to your service (as below - Option- A) or should we accept individual parameters as in option - B:
Option - A:
#GET
#Produces("text/plain")
public String hello(#Context HttpServletRequest req) {
}
Option - B
#GET
#Produces("text/plain")
public String hello(#PathParam("id") int id, #BeanParam etc.) {
}
I think it's better to leverage support provided by JAX-RS to extract content from request than working directly on the request object. This will remove some technical plumbing and you will be able to focus on your own processing.
Moreover the Servlet API isn't really REST oriented. I mean, for example, regarding path variables / parameters, you need to extract them by your own.
Hope it helps you,
Thierry
A rest resource is generally identified by its name and the path parameters(optional).
Example : /tweets/{123} - This indicates 'Give me a tweet from the tweets collection identified by its id(123)'
The rest style of design might not mandate the service provider to expose the resource through path/query parameters but the general idea is that the path parameters uniquely identify a resource and query parameters are to be used as filters.
In your case, the obvious choice would be is to go for path parameters but you should use the injected request object only for the purpose of keeping track of things like remote user, session id etc.. which would not be used to identify the resource but something which will be used internally.
I used the suggested approach in this question to return HATEOAS formatted outputs that match those returned by spring-data-rest. It works good, but is there a way to avoid boiler plate code to create entity resource assemblers like the QuestionResourceAssembler in the referenced question, if I only want to add 'self' links using the id to all entities? Perhaps using ResourceAssemblerSupport?
The easiest way is to simply use the Resource wrapper type:
Resource<Person> personResource = new Resource<>(person);
personResource.addLink(…);
personResource.addLink(…);
Links can be created either by simply instantiating them (i.e. new Link("http://localhost/foo", "relation") or by using the ControllerLinkBuilder which allows you to point to Controller methods for obtain a reverse mapping. See this section of the Readme for details.
I'm wondering where to put the edit, and new keywords by rest application. I'll use express-resource in a project, and the default settings are these:
GET /forums -> index
GET /forums/new -> new
POST /forums -> create
GET /forums/:forum -> show
GET /forums/:forum/edit -> edit
PUT /forums/:forum -> update
DELETE /forums/:forum -> destroy
There is a problem with this solution: there is not a real resource behind the new and edit. I mean the URL-s refer to resources, and after any slash is a sub-resource.
For example:http://my.example.com/users/1 represents:
var firstUser = {
name: "John Smith",
birthDate: new Date(1952,10,4),
hobbies: ["skiing", "football"],
...
}
And http://my.example.com/users/1/birthDate represents:
firstUser.birthDate
But by http://my.example.com/users/1/edit there is no such property:
firstUser.edit
So something is wrong with this conception.
Where is the real place of these keywords? In queryString or in headers?
From the perspective of a REST API these do not exist anywhere as they are not related to the representation of resources. They are actions upon resources and therefore expressed by the HTTP methods used. They would not bee needed if you were to create an external client that uses the API.
There is likely a need to provide some support for this type of functionality so that something like a UI could be presented, but that is the concern of the particular application and not the API itself. At that point it becomes discretionary but I would certainly avoid using headers as that would be pretty outside of conventional practice. But by headers it appears that you actually meant URI path. Out of those 2 I would say the path is the better option since it clearly defines any type of UI as a distinct resource and would keep it apart from the clean API, while using a query string on a part of the API would more tightly (mistakenly) associate it with the underlying resource.
Some update after a year or so:
edit and new should be hyperlinks
these links are just the representations of possible operation calls
by following them it is possible to manipulate the resource they belong by sending representations of the intended resource state, and/or by calling the proper methods
these terms are no resources, they don't have their own URL (resource identifier)
Thanks the advices Matt Whipple!
I think the best way to learn REST is reading the Fielding dissertation. There are many tutorials out there, but the authors of most of these does not really understand REST.