@Detailed explanation of the use of transactional annotation

@Transactional The scope of action of

1. Method ： It is recommended to use annotations on methods , But here's the thing ： This annotation can only be applied to public On the way , Otherwise it doesn't work .
2. class ： If this annotation is used on a class , Indicates that the annotation is valid for all public All methods work .
3. Interface ： It is not recommended to use .

@Transactional Summary of common configuration parameters of （ It only lists 5 I usually use it ）：

Property name

explain

propagation

The spread of transactions , The default value is REQUIRED, Optional values are described above

isolation

The isolation level of the transaction , Default value adopts DEFAULT, Optional values are described above

timeout

Transaction timeout , The default value is -1（ No timeout ）. If the time limit is exceeded but the transaction has not completed , Then automatically roll back the transaction .

readOnly

Specifies whether the transaction is read-only , The default value is false.

rollbackFor

Used to specify the exception type that can trigger transaction rollback , And you can specify multiple exception types .

@Transactional Transaction annotation principle

During the interview, I was asking AOP One of the questions that may be asked is . In a nutshell ！

We know ,@Transactional The working mechanism of is based on AOP Realized ,AOP It is also implemented by using dynamic proxy . If the target object implements the interface , By default... Is used JDK Dynamic proxy for , If the target object does not implement the interface , Will use CGLIB A dynamic proxy .

If a class or a class of public Methods are marked with @Transactional Annotations of words ,Spring The container will create a proxy class for it at startup time , In the call by @Transactional Annotated public Method time , What's actually called is ,TransactionInterceptor Class invoke() Method . The function of this method is to start the transaction before the target method , If an exception is encountered during the execution of the method, the transaction will be rolled back , After the method call completes, the transaction is committed .

TransactionInterceptor Class invoke() The actual call inside the method is TransactionAspectSupport Class invokeWithinTransaction() Method .

Spring AOP Self call problem

If the others in the same category do not @Transactional The internal calls of the annotated methods are @Transactional Method of annotation , Yes @Transactional Transactions of annotated methods will fail .

This is because Spring AOP Agency , Because only when @Transactional When annotated methods are called outside the class ,Spring Business management takes effect .

MyService Class method1() call method2() It will lead to method2() Transaction failure for .

@Service
public class MyService {

private void method1() {
     method2();
     //......
}
@Transactional
 public void method2() {
     //......
  }
}

The solution is to avoid self calling or using AspectJ replace Spring AOP agent .

@Transactional A summary of the precautions in the use of

• @Transactional Annotations only apply to public The transaction takes effect on the method , It is not recommended to use ;
• Avoid calling in the same class @Transactional Method of annotation , This will cause the transaction to fail ;
• The right settings @Transactional Of rollbackFor and propagation attribute , Otherwise, the transaction may fail to roll back ;
• By @Transactional The class of the annotated method must be Spring management , Otherwise it doesn't work ;
• The underlying database must support transaction mechanism , Otherwise it doesn't work ;