Spring Singleton @Transactional并发访问

Question

In a Spring 3 MVC web application scenario with @Controller , @Service, @Repository if I am annotating the @Service classes with @Transactional and leave the scope of bean to be a Singleton, would the transaction manager block the service method in case of concurrent accesses?

In case of singleton, as there would be one instance of Service class in the application context at any point of time, a subsequent request by a different thread, to the same service method which is already executing inside a transaction need to wait till the service method completes processing, please let me know if this true.

I have just started looking into Java EE 6 with @Stateless EJBs being used for service classes, and comparing it with how things are done in Spring.

Answer 1

@Transactional specify that method code is executed in transaction. There are different transaction isolation levels which specify the behavior of the method according to the underlying datastore (isolation property of @Transactional annotation).

The are next isolation levels: http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/transaction/annotation/Isolation.html .

This isolation levels are referred to underlying data store, not to the method.

The most aggressive isolation level is serializable: A constant indicating that dirty reads, non-repeatable reads and phantom reads are prevented. This level includes the prohibitions in ISOLATION_REPEATABLE_READ and further prohibits the situation where one transaction reads all rows that satisfy a WHERE condition, a second transaction inserts a row that satisfies that WHERE condition, and the first transaction rereads for the same condition, retrieving the additional "phantom" row in the second read. ( http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/transaction/annotation/Isolation.html#SERIALIZABLE )

If you want to limit access to this method maybe you should simply use synchronized keyword.