Simple app with authorization and session management
In this extended example you will see how to create a simple authorization app with login/sign up scenarios
and session management.
DataKernel doesn’t include built-in authorization modules or solutions, as this process may significantly vary depending
on the project’s business logic. This example represents a simple “best practice” which you
can extend and modify depending on your needs. You can find full example sources on GitHub.
In the example we will consider only the server which was created using DataKernel HttpServerLauncher and
AsyncServlet. This approach allows to create an embedded application server in about 100 lines of code with no
additional XML configurations or third-party dependencies.
Let’s create an AuthLauncher, which is the main part of the application as it manages the application lifecycle, routing
and authorization processes. We will use DataKernel HttpServerLauncher and extend it:
The following objects are provided:
AuthService - authorization and register logic
Executor - needed for StaticLoader
StaticLoader - loads static content from /site directory
SessionStore - handy storage for information about sessions
AsyncServletservlet - the main servlet that combines public and private servlets (for authorized and
unauthorized sessions). As you can see, due to DI, this servlet only requires two servlets without their own dependencies
Now let’s provide the public and private servlets.
Let’s take a closer look at how we set up routing for servlets. DataKernel approach resembles Express. For example,
here’s the request to the homepage for unauthorized users:
Method map(@Nullable HttpMethod method, String path, AsyncServlet servlet) adds the route to the RoutingServlet:
method (optional) is one of the HTTP methods (GET, POST etc)
path is the path on the server
servlet defines the logic of request processing. If you need to get some data from the request while processing you can use:
request.getPathParameter(String key)/request.getQueryParameter(String key) (see example of query parameter usage)
to provide the key of the needed parameter and receive back a corresponding String
request.getPostParameters() to get a Map of all request parameters
GET requests with paths “/login” and “/signup” upload the needed HTML pages.
POST requests with paths “/login” and “/signup” take care of log in and sign up logic respectively:
Pay attention at POST“/login” rout. serveFirstSuccessful() takes two servlets and waits until one of them
finishes processing successfully. So if authorization fails, a Promise of null will be returned (AsyncServlet.NEXT),
which means fail. In this case, a simple StaticServlet will be created to load the errorPage.
Successful log in will generate a session id for the user and will save string "My saved object in session" to session store.
Also it will redirect user to “/members”.
Now, let’s get to the next servlet that handles authorized sessions.
First, it redirects requests from homepage to “/members”:
Next, it takes care of all of the requests that go after “/members” path:
Pay attention to the path “/members/*“.
* is a variable for the next part of the path. It states that this servlet will process any path segment that goes after “/members/”.
For example, this route:
is a GET request for “/members/cookie” path. This request shows all cookies stored in the session.
A request can have an attachment map where any content can be mapped to some type, i.e. String.
By default, requests have no attachments.
In this case, the request contains 'cookies' as an attachment that's mapped to the `String` type.
“/members/logout” logs the user out, deletes all cookies related to this session and redirects the user to the homepage.
After public and private servlets are set up, we define main() method, which will start our launcher:
Running the application
If you want to run the example, clone DataKernel and import it
as a Maven project. Check out branch v3.0. Before running the example, build the project (Ctrl + F9 for IntelliJ IDEA).
Open AuthLauncher class and run its main() method.
Then open your favorite browser and go to localhost:8080. Try to sign up and then log in. When
logged in, check out your saved cookies for session. You will see the following content: My saved object in session.
Finally, try to log out. You can also try to log in with an invalid login or password.