If you're new to Apache Shiro, this short tutorial will show you how to set up an initial and very simple application secured by Apache Shiro. We'll discuss Shiro's core concepts along the way to help familiarize you with Shiro's design and API.
If you don't want to actually edit files as you follow this tutorial, you can obtain a nearly identical sample application and reference it as you go. Choose a location:
- In Apache Shiro's Git repository: https://github.com/apache/shiro/tree/master/samples/quickstart
- In Apache Shiro's source distribution's samples/quickstart directory. The source distribution is available from the Download page.
In this simple example, we'll create a very simple command-line application that will run and quickly exit, just so you can get a feel for Shiro's API.
Apache Shiro was designed from day one to support any application - from the smallest command-line applications to the largest clustered web applications. Even though we're creating a simple app for this tutorial, know that the same usage patterns apply no matter how your application is created or where it is deployed.
This tutorial requires Java 1.5 or later. We'll also be using Apache Maven as our build tool, but of course this is not required to use Apache Shiro. You may acquire Shiro's .jars and incorporate them in any way you like into your application, for example maybe using Apache Ant and Ivy.
For this tutorial, please ensure that you are using Maven 2.2.1 or later. You should be able to type mvn --version in a command prompt and see something similar to the following:
For now, create a new directory on your filesystem, for example, shiro-tutorial and save the following Maven pom.xml file in that directory:
We'll be running a simple command-line application, so we'll need to create a Java class with a public static void main(String args) method.
In the same directory containing your pom.xml file, create a *src/main/java sub directory. In src/main/java create a Tutorial.java file with the following contents:
Don't worry about the import statements for now - we'll get to them shortly. But for now, we've got a typical command line program 'shell'. All this program will do is print out the text "My First Apache Shiro Application" and exit.
To try our Tutorial application, execute the following in a command prompt in your tutorial project's root dirctory (e.g. shiro-tutorial), and type the following:
mvn compile exec:java
And you will see our little Tutorial 'application' run and exit. You should see something similar to the following (notice the bold text, indicating our output):
We've verified the application runs successfully - now let's enable Apache Shiro. As we continue with the tutorial, you can run mvn compile exec:java after each time we add some more code to see the results of our changes.
The first thing to understand in enabling Shiro in an application is that almost everything in Shiro is related to a central/core component called the SecurityManager. For those familiar with Java security, this is Shiro's notion of a SecurityManager - it is NOT the same thing as the java.lang.SecurityManager.
While we will cover Shiro's design in detail in the Architecture chapter, it is good enough for now to know that the Shiro SecurityManager is the core of a Shiro environment for an application and one SecurityManager must exist per application. So, the first thing we must do in our Tutorial application is set-up the SecurityManager instance.
While we could instantiate a SecurityManager class directly, Shiro's SecurityManager implementations have enough configuration options and internal components that make this a pain to do in Java source code - it would be much easier to configure the SecurityManager with a flexible text-based configuration format.
To that end, Shiro provides a default ‘common denominator’ solution via text-based INI configuration. People are pretty tired of using bulky XML files these days, and INI is easy to read, simple to use, and requires very few dependencies. You’ll also see later that with a simple understanding of object graph navigation, INI can be used effectively to configure simple object graphs like the SecurityManager.
Many Configuration Options
Shiro's SecurityManager implementations and all supporting components are all JavaBeans compatible. This allows Shiro to be configured with practically any configuration format such as XML (Spring, JBoss, Guice, etc), YAML, JSON, Groovy Builder markup, and more. INI is just Shiro's 'common denominator' format that allows configuration in any environment in case other options are not available.
So we'll use an INI file to configure the Shiro SecurityManager for this simple application. First, create a src/main/resources directory starting in the same directory where the pom.xml is. Then create a shiro.ini file in that new directory with the following contents:
As you see, this configuration basically sets up a small set of static user accounts, good enough for our first application. In later chapters, you will see how we can use more complex User data sources like relational databases, LDAP an ActiveDirectory, and more.
Now that we have an INI file defined, we can create the SecurityManager instance in our Tutorial application class. Change the main method to reflect the following updates:
And there we go - Shiro is enabled in our sample application after adding only 3 lines of code! How easy was that?
Feel free to run mvn compile exec:java and see that everything still runs successfully (due to Shiro's default logging of debug or lower, you won't see any Shiro log messages - if it starts and runs without error, then you know everything is still ok).
Here is what the above additions are doing:
- We use Shiro's IniSecurityManagerFactory implementation to ingest our shiro.ini file which is located at the root of the classpath. This implementation reflects Shiro's support of the Factory Method Design Pattern. The classpath: prefix is an resource indicator that tells shiro where to load the ini file from (other prefixes, like url: and file: are supported as well).
- The factory.getInstance() method is called, which parses the INI file and returns a SecurityManager instance reflecting the configuration.
- In this simple example, we set the SecurityManager to be a static (memory) singleton, accessible across the JVM. Note however that this is not desireable if you will ever have more than one Shiro-enabled application in a single JVM. For this simple example, it is ok, but more sophisticated application environments will usually place the SecurityManager in application-specific memory (such as in a web app's ServletContext or a Spring, Guice or JBoss DI container instance).
Now that our SecurityManager is set-up and ready-to go, now we can start doing the things we really care about - performing security operations.
When securing our applications, probably the most relevant questions we ask ourselves are “Who is the current user?” or “Is the current user allowed to do X”? It is common to ask these questions as we're writing code or designing user interfaces: applications are usually built based on user stories, and you want functionality represented (and secured) based on a per-user basis. So, the most natural way for us to think about security in our application is based on the current user. Shiro’s API fundamentally represents the notion of 'the current user' with its Subject concept.
In almost all environments, you can obtain the currently executing user via the following call:
Using SecurityUtils.getSubject(), we can obtain the currently executing Subject. Subject is a security term that basically means "a security-specific view of the currently executing user". It is not called a 'User' because the word 'User' is usually associated with a human being. In the security world, the term 'Subject' can mean a human being, but also a 3rd party process, cron job, daemon account, or anything similar. It simply means 'the thing that is currently interacting with the software'. For most intents and purposes though, you can think of the Subject as Shiro’s ‘User’ concept.
The getSubject() call in a standalone application might return a Subject based on user data in an application-specific location, and in a server environment (e.g. web app), it acquires the Subject based on user data associated with current thread or incoming request.
Now that you have a Subject, what can you do with it?
If you want to make things available to the user during their current session with the application, you can get their session:
The Session is a Shiro-specific instance that provides most of what you're used to with regular HttpSessions but with some extra goodies and one big difference: it does not require an HTTP environment!
If deploying inside a web application, by default the Session will be HttpSession based. But, in a non-web environment, like this simple tutorial application, Shiro will automatically use its Enterprise Session Management by default. This means you get to use the same API in your applications, in any tier, regardless of deployment environment! This opens a whole new world of applications since any application requiring sessions does not need to be forced to use the HttpSession or EJB Stateful Session Beans. And, any client technology can now share session data.
So now you can acquire a Subject and their Session. What about the really useful stuff like checking if they are allowed to do things, like checking against roles and permissions?
Well, we can only do those checks for a known user. Our Subject instance above represents the current user, but who is the current user? Well, they're anonymous - that is, until they log in at least once. So, let's do that:
That's it! It couldn't be easier.
But what if their login attempt fails? You can catch all sorts of specific exceptions that tell you exactly what happened and allows you to handle and react accordingly:
There are many different types of exceptions you can check, or throw your own for custom conditions Shiro might not account for. See the AuthenticationException JavaDoc for more.
Security best practice is to give generic login failure messages to users because you do not want to aid an attacker trying to break into your system.
Ok, so by now, we have a logged in user. What else can we do?
Let's say who they are:
We can also test to see if they have specific role or not:
We can also see if they have a permission to act on a certain type of entity:
Also, we can perform an extremely powerful instance-level permission check - the ability to see if the user has the ability to access a specific instance of a type:
Piece of cake, right?
Finally, when the user is done using the application, they can log out:
After adding in the above code examples, here is our final Tutorial class file. Feel free to edit and play with it and change the security checks (and the INI configuration) as you like:
Hopefully this introduction tutorial helped you understand how to set-up Shiro in a basic application as well Shiro's primary design concepts, the Subject and SecurityManager.
But this was a fairly simple application. You might have asked yourself, "What if I don't want to use INI user accounts and instead want to connect to a more complex user data source?"
To answer that question requires a little deeper understanding of Shiro's architecture and supporting configuration mechanisms. We'll cover Shiro's Architecture next.