I want to know what actually happens when you annotate a method with `@Transactional`?
Of course, I know that Spring will wrap that method in a Transaction.

But, I have the following doubts:

1. I heard that Spring creates a **proxy class**? Can someone explain this in more **depth**. **What actually resides in that proxy class? What happens to the actual class? And how can I see Spring's created proxied class**
2. I also read in Spring docs that:

> 
> *Note: Since this mechanism is based on proxies, **only 'external' method calls coming in through the proxy will be intercepted**. This means that 'self-invocation', i.e. a method within the target object calling some other method of the target object, won't lead to an actual transaction at runtime even if the invoked method is marked with `@Transactional`!*
> 
> 
> 

Source: <http://static.springsource.org/spring/docs/2.0.x/reference/transaction.html>

**Why only external method calls will be under Transaction and not the self-invocation methods?**
['https://Stackoverflow.com/questions/1099025', 'https://Stackoverflow.com', 'https://Stackoverflow.com/users/133830/']
When Spring loads your bean definitions, and has been configured to look for `@Transactional` annotations, it will create these **proxy objects** around your actual **bean**. These proxy objects are instances of classes that are auto-generated at runtime. The default behaviour of these proxy objects when a method is invoked is just to invoke the same method on the "target" bean (i.e. your bean). 

However, the proxies can also be supplied with interceptors, and when present these interceptors will be invoked by the proxy before it invokes your target bean's method. For target beans annotated with `@Transactional`, Spring will create a `TransactionInterceptor`, and pass it to the generated proxy object. So when you call the method from client code, you're calling the method on the proxy object, which first invokes the `TransactionInterceptor` (which begins a transaction), which in turn invokes the method on your target bean. When the invocation finishes, the `TransactionInterceptor` commits/rolls back the transaction. It's transparent to the client code.

As for the "external method" thing, if your bean invokes one of its own methods, then it will not be doing so via the proxy. Remember, Spring wraps your bean in the proxy, your bean has no knowledge of it. Only calls from "outside" your bean go through the proxy.

Does that help?
As a visual person, I like to weigh in with a sequence diagram of the proxy pattern. If you don't know how to read the arrows, I read the first one like this: `Client` executes `Proxy.method()`.

1. The client calls a method on the target from his perspective, and is silently intercepted by the proxy
2. If a before aspect is defined, the proxy will execute it
3. Then, the actual method (target) is executed
4. After-returning and after-throwing are optional aspects that are
executed after the method returns and/or if the method throws an
exception
5. After that, the proxy executes the after aspect (if defined)
6. Finally the proxy returns to the calling client

![Proxy Pattern Sequence Diagram](https://i.imgur.com/Ye9pEVI.jpg)
(I was allowed to post the photo on condition that I mentioned its origins. Author: Noel Vaes, website: <https://www.noelvaes.eu>)