Week 4 - Singleton Session Beans

Question 1

Why use a singleton session bean?

Answer 1

To create a shared instance for all clients.

Question 2

What is AtomicInteger?

Answer 2

some data structures from java.util.concurrent are thread-safe

AtomicInteger shared = new AtomicInteger(1);
public int increment() {
return shared.incrementAndGet();
}

Question 3

What is a problem with using synchronized or locks for concurrency?

Answer 3

Bottlenecks

Question 4

What is container-managed concurrency?

Answer 4

The default for singleton session beans.

Annotate class or methods with:
@jakarta.ejb.Lock(locktype)

locktype is an enum defined in jakarta.ejb.LockType

READ allows concurrent access to all requests

WRITE (default) defines lock that can be held by one
thread at a time

Question 5

What is bean managed concurrency?

Answer 5

@jakarta.ejb.ConcurrencyManagement(BEAN)

make bean thread-safe manually using tools from java.util.concurrent

Question 6

What other session bean has the same lifecycle as a singleton session bean?

Answer 6

Stateless session bean
(Does not exist OR method-ready)

Question 7

What are value objects (data transfer objects)?

Answer 7

DTOs (Data Transfer Objects) are simple objects that carry data between different parts of a system. They are especially useful when transferring data reliably, ensuring that values (like a URL) remain consistent and unmodified during the transfer. Since some types, like URLs, are mutable, it’s important to copy them before passing them along to prevent unexpected changes.

Question 8

Singleton beans are suitable for caching RSS feeds (T or F)

Answer 8

T

Question 9

What is an RSS feed?

Answer 9

An RSS feed (Really Simple Syndication) is a way for websites to share their latest content with you automatically, without you needing to visit the site directly.