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    <p>Firstly I'm assuming that you meant to say that the <code>Cart</code> bean is Session scoped (your example says that it is request scoped, but that doesn't seem to make sense) and that <code>CartService</code> is a singleton.</p> <p>If we think about how your user interacts with the application, do we actually have a need to perform any synchronization on a <code>Cart</code> instance?</p> <p>We definitely do not need to make <code>CartService.addItem()</code> synchronized as we're relying on Spring's proxy injection to ensure that the <code>Cart</code> instance from the current Session is injected during the Thread of execution, so no worries there.</p> <p>So our question of synchronization is about whether there is a scenario during a single Session that requires us to synchronize adding of items to a <code>Cart</code>? </p> <p>I assume that your Session is being driven by the user's browser. There is no way legitimate way to share a single Session between different browsers. So apart from having multiple tabs open, it is highly likely that your user will be adding items to their <code>Cart</code> in a sequential manner. Even if they did open multiple tabs and enter items is there a problem? Once the user initiates your "checkout" process, you can block adding more items to the <code>Cart</code> and then ask the user to confirm that the <code>Cart</code> they are about to checkout is correct, giving them the opportunity to remove any dubious items.</p> <p>If you still decide that you really need synchronization on the <code>Cart</code> then I would do the following:</p> <pre><code>public class Cart { private HashSet&lt;Item&gt; items = new HashSet&lt;Item&gt;(); public synchronized void addItem(Item item) { items.add(item); } } </code></pre> <p>That way you easily synchronize access to the <code>Set</code> within the <code>Cart</code> class.</p>
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    1. PObest practice for thread safe session bean in spring?
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    1. USRob Blake
    1. USRob Blake
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    1. COYou're assumption was correct. I edited the scope in my question. And I just quickly want to say Yes there are plenty of scenarios where multiple threads access a session scoped bean of one session. Putting the synchronization into the model bean is not really acceptable, as it's more likely to have concurrency issues in the service.
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      1. USMarkus Malkusch
 

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