Concurrency Support

In most environments, Security is stored on a per-Thread basis. This means that when work is done on a new Thread, the SecurityContext is lost. Spring Security provides some infrastructure to help make this much easier to manage. Spring Security provides low-level abstractions for working with Spring Security in multi-threaded environments. In fact, this is what Spring Security builds on to integrate with AsyncContext.start(Runnable) and Spring MVC Async Integration.

DelegatingSecurityContextRunnable

One of the most fundamental building blocks within Spring Security’s concurrency support is the DelegatingSecurityContextRunnable. It wraps a delegate Runnable to initialize the SecurityContextHolder with a specified SecurityContext for the delegate. It then invokes the delegate Runnable, ensuring to clear the SecurityContextHolder afterwards. The DelegatingSecurityContextRunnable looks something like this:

public void run() {
try {
	SecurityContextHolder.setContext(securityContext);
	delegate.run();
} finally {
	SecurityContextHolder.clearContext();
}
}

While very simple, it makes it seamless to transfer the SecurityContext from one Thread to another. This is important since, in most cases, the SecurityContextHolder acts on a per-Thread basis. For example, you might have used Spring Security’s <global-method-security> support to secure one of your services. You can now transfer the SecurityContext of the current Thread to the Thread that invokes the secured service. The following example show how you might do so:

Runnable originalRunnable = new Runnable() {
public void run() {
	// invoke secured service
}
};

SecurityContext context = SecurityContextHolder.getContext();
DelegatingSecurityContextRunnable wrappedRunnable =
	new DelegatingSecurityContextRunnable(originalRunnable, context);

new Thread(wrappedRunnable).start();

The preceding code:

Creates a Runnable that invokes our secured service. Note that it is not aware of Spring Security.
Obtains the SecurityContext that we wish to use from the SecurityContextHolder and initializes the DelegatingSecurityContextRunnable.
Uses the DelegatingSecurityContextRunnable to create a Thread.
Starts the Thread we created.

Since it is common to create a DelegatingSecurityContextRunnable with the SecurityContext from the SecurityContextHolder, there is a shortcut constructor for it. The following code has the same effect as the preceding code:

Runnable originalRunnable = new Runnable() {
public void run() {
	// invoke secured service
}
};

DelegatingSecurityContextRunnable wrappedRunnable =
	new DelegatingSecurityContextRunnable(originalRunnable);

new Thread(wrappedRunnable).start();

The code we have is simple to use, but it still requires knowledge that we are using Spring Security. In the next section we will take a look at how we can utilize DelegatingSecurityContextExecutor to hide the fact that we are using Spring Security.

DelegatingSecurityContextExecutor

In the previous section, we found that it was easy to use the DelegatingSecurityContextRunnable, but it was not ideal since we had to be aware of Spring Security to use it. Now we look at how DelegatingSecurityContextExecutor can shield our code from any knowledge that we are using Spring Security.

The design of DelegatingSecurityContextExecutor is similar to that of DelegatingSecurityContextRunnable, except that it accepts a delegate Executor instead of a delegate Runnable. The following example shows how to use it:

SecurityContext context = SecurityContextHolder.createEmptyContext();
Authentication authentication =
	UsernamePasswordAuthenticationToken.authenticated("user","doesnotmatter", AuthorityUtils.createAuthorityList("ROLE_USER"));
context.setAuthentication(authentication);

SimpleAsyncTaskExecutor delegateExecutor =
	new SimpleAsyncTaskExecutor();
DelegatingSecurityContextExecutor executor =
	new DelegatingSecurityContextExecutor(delegateExecutor, context);

Runnable originalRunnable = new Runnable() {
public void run() {
	// invoke secured service
}
};

executor.execute(originalRunnable);

This code:

Note that, in this example, we create the SecurityContext by hand. However, it does not matter where or how we get the SecurityContext (for example, we could obtain it from the SecurityContextHolder). * Creates a delegateExecutor that is in charge of executing submitted Runnable objects. * Finally, we create a DelegatingSecurityContextExecutor, which is in charge of wrapping any Runnable that is passed into the execute method with a DelegatingSecurityContextRunnable. It then passes the wrapped Runnable to the delegateExecutor. In this case, the same SecurityContext is used for every Runnable submitted to our DelegatingSecurityContextExecutor. This is nice if we run background tasks that need to be run by a user with elevated privileges. * At this point, you may ask yourself, “How does this shield my code of any knowledge of Spring Security?” Instead of creating the SecurityContext and the DelegatingSecurityContextExecutor in our own code, we can inject an already initialized instance of DelegatingSecurityContextExecutor.

Consider the following example:

@Autowired
private Executor executor; // becomes an instance of our DelegatingSecurityContextExecutor

public void submitRunnable() {
Runnable originalRunnable = new Runnable() {
	public void run() {
	// invoke secured service
	}
};
executor.execute(originalRunnable);
}

Now our code is unaware that the SecurityContext is being propagated to the Thread, the originalRunnable is run, and the SecurityContextHolder is cleared out. In this example, the same user is being used to run each thread. What if we wanted to use the user from SecurityContextHolder (that is, the currently logged in-user) at the time we invoked executor.execute(Runnable) to process originalRunnable? You can do so by removing the SecurityContext argument from our DelegatingSecurityContextExecutor constructor:

SimpleAsyncTaskExecutor delegateExecutor = new SimpleAsyncTaskExecutor();
DelegatingSecurityContextExecutor executor =
	new DelegatingSecurityContextExecutor(delegateExecutor);

Now, any time executor.execute(Runnable) is run, the SecurityContext is first obtained by the SecurityContextHolder and then that SecurityContext is used to create our DelegatingSecurityContextRunnable. This means that we are running our Runnable with the same user that was used to invoke the executor.execute(Runnable) code.

Spring Security Concurrency Classes

See the Javadoc for additional integrations with both the Java concurrent APIs and the Spring Task abstractions. They are self-explanatory once you understand the previous code.