How to apply @transactional transaction annotation to perfection?

I was busy at work two days ago , involves @Transactional Control of transactions , He studied it carefully , Quite a gain , It took several days to test and sort out , Just published today , Hope to see the old iron bloggers get something . Don't talk too much, go straight to the point .

Just a quick introduction Spring The spread of transactions ：

The so-called communication of affairs refers to , If before starting the current transaction , A transaction context already exists , There are several options to specify the execution behavior of a transactional method . stay TransactionDefinition Several constants representing propagation behavior are included in the definition ：
1、TransactionDefinition.PROPAGATION_REQUIRED： If there are currently transactions , Then join the transaction ; If there is no current transaction , Create a new transaction . This is the default .
2、’TransactionDefinition.PROPAGATION_REQUIRES_NEW： Create a new transaction , If there are currently transactions , Suspend the current transaction .
3、TransactionDefinition.PROPAGATION_SUPPORTS： If there are currently transactions , Then join the transaction ; If there is no current transaction , Continue to run in a non transactional manner .
4、TransactionDefinition.PROPAGATION_NOT_SUPPORTED： Run in a non transactional manner , If there are currently transactions , Suspend the current transaction .
TransactionDefinition.PROPAGATION_NEVER： Run in a non transactional manner , If there are currently transactions , Throw an exception .
5、TransactionDefinition.PROPAGATION_MANDATORY： If there are currently transactions , Then join the transaction ; If there is no current transaction , Throw an exception .
6、TransactionDefinition.PROPAGATION_NESTED： If there are currently transactions , Create a transaction to run as a nested transaction of the current transaction ; If there is no current transaction , Then the value is equivalent to TransactionDefinition.PROPAGATION_REQUIRED.

And then say Spring Transaction rollback mechanism ：

Spring Of AOP That is, declarative transaction management is for by default unchecked exception Roll back .Spring The transaction boundary starts before calling the business method , After the execution of the business method, execute commit or rollback(Spring The default depends on whether to throw runtimeException).

If you have try{}catch(Exception e){} Handle , that try The code block inside is separated from transaction management , In order for the transaction to take effect, it needs to be in catch in throw new RuntimeException (“xxxxxx”); This is also the scenario of failure of affairs that will be asked in the interview .

Let me give you a brief introduction @Transactional Annotate the underlying implementation , without doubt , It's through dynamic proxy , Then dynamic agents are divided into JDK Self and CGLIB, I won't repeat this much , After all, today's theme is how to @Transactional The control of things is applied to perfection . ha-ha ~

The first thing to note is that @Transactional In the method of annotation , Then call other methods in this class method2 when , that method2 Method @Transactional Annotation is not ！ Meeting ！ raw ！ effect ！ Of ！ But plus, it won't report an error , Take pictures to help you understand . This is also the scenario of failure of affairs that will be asked in the interview .
![ Insert picture description here ](https://img-blog.csdnimg.cn/94e62f6f50dc4bfd806df8a869113afe.png#pic_center
Method enhancement before and after the target object through the proxy object , That is, transaction initiation, commit and rollback . So what about continuing to call other methods in this class , Here's the picture ：

It can be seen that the self call inside the target object , That is, through this. The target object pointed to will not perform the enhancement of the method .

Let's start with the second point that needs attention , Let's talk about how to solve the problem of the first point above . The second point is @Transactional The method of annotation must be a public method , It has to be public Modifier ！！！

As for the reason for this , Express your personal understanding , because JVM The dynamic agent is implemented based on the interface , The target method is enhanced through the proxy class , Think about it, too , No access, so what do you want me to do ,,, ok , I didn't go deep into this , Personal understanding personal understanding .

Let me also put a question here , I hope some experts can reply and instruct me , because JVM Dynamic proxies are implemented based on interfaces , So is it service All layers should follow the development mode of interface and implementation class , The annotation will take effect , That is to say controller The layer directly calls the without interface service layer , It doesn't work with annotations , This is lazy , No test , One is because no one will develop it like this , Second, I think it doesn't work , ha-ha

Let's solve the first problem , How to call other methods in this class in a method .

adopt AopContext.currentProxy () Get the proxy object of this class , Just call again . Because this is CGLIB Realization , So turn on AOP, It's also very simple , stay springboot Annotate the startup class @EnableAspectJAutoProxy(exposeProxy = true) That's all right. , It depends on you to search it by yourself . it is to be noted that , Be careful , The method called by the proxy object should also be public Modifier , Otherwise, the injected... Cannot be obtained in the method bean, A null pointer error will be reported .

emmmm, Let me talk about the method and result of the call first . I simply wrote the code myself , It's a little rough , Don't mind , Hey ...

Controller Call in Service

Service Realize the control of transactions in ： Interface

Service Realize the control of transactions in ： Implementation class （ Descriptions of various situations are written in the picture , It's easy to read , Help you understand quickly ）

In the above two cases, the method is called without proxy 1 And methods 2, Method transactionalMethod All in one transaction , All four update operations failed .

Then someone may have questions , In the method 1 And methods 2 Plus all @Transactional What about the notes ？ The answer is that the result is consistent with the above .

Summary as long as the method transactionalMethod There's a note on it , And the way 1 And methods 2 Are in the current transaction （ Do not use proxy to call , Method 1 And methods 2 Upper @Transactional Annotations are not valid ; Using agents , Need method 1 And methods 2 All in transactionalMethod Method , Either default or nested transactions , Of course, it can be omitted @Transactional annotation ）, So keep transaction consistency as a whole .

If you want a way 1 And methods 2 How to keep the transaction consistency separately , I just said , If you don't call with a proxy @Transactional Annotations are not valid , So be sure to use proxy calls to implement , Then let the method 1 And methods 2 Open new transactions separately , then OK La . Put the picture below .

Both cases are methods 1 And methods 2 Are in separate transactions , Keep the consistency of transactions .

Next, further optimization , Can be in transactionalMethod In the method, the method 1 And methods 2 Control . The art of code should be brought into full play , Let's start .

The code is too long , Beyond the screen , Paste out the screenshot , The red box notes need to be read carefully , I hope it doesn't affect your reading experience , thus , This article is about @Transactioinal That's all for annotations ,

Let's summarize briefly ：

1、 Namely @Transactional Annotations ensure that each method is in a transaction , If there is try It must be catch Throw a runtime exception in .

2、 The method must be public Modifier . Otherwise the annotation will not take effect , But there's nothing wrong with adding notes , No mistake. , It's just useless .

3、this. The call of this method , The annotation on the called method does not take effect , Because the slice enhancement cannot be performed again .

If there is more detailed discussion, please comment , Thank you for reading .