[JAVA] How to make @Transactional work that does not work if you use it incorrectly

The Spring annotation " @ Transactional "is convenient because it automatically executes a transaction just by attaching it to a method and rolls back when a RuntimeException occurs by default. However, there are cases where the transaction cannot be performed just by adding `` `@ Transactional, and it does not cause a build error, so when I actually moved it, the transaction was not performed. So, I have summarized how to use `` `@ Transactional``` to work.

Conditions for `` `@ Transactional``` to work

After moving it around and checking it, it seems that the following conditions must be met.

--It must be a public method of the class you are DI --Called directly by another class or framework that is DI

Public method of DI class

There is also a method of using Bean definition file as a method of DI class, but here we will describe the implementation using Spring annotation.

ServiceClass.java

@Service
public class ServiceClass {

    @Transactional
	public void updateDB() {
    	//DB update process
	}
}

In the above, `@ Service``` is attached to the class, but other annotations that do DI such as @ Controller``` and `` @ Repository``` will also work.

Call directly from another class that is DI

The class that calls the above ServiceClass is as follows.

ControllerClass.java

@RequestMapping("/sample/*")
@Controller
public class ControllerClass {

	@Autowired
	ServiceClass serviceClass;

    @RequestMapping(value = { "index" })
    public String index(){
    	serviceClass.updateDB();

        return "sample/index";
    }
}

This is also a class that is DI using `` `@ Controller. @autowired```The transaction works by automatically creating an instance of serviceclass using and calling the updatedb method.

Call directly from the framework

It also works when a method with @ Transactional is called from the Spring framework. In the following cases, the transaction operates when the request corresponding to the setting of @ RequestMapping comes and the method is called.

ControllerClass.java

@RequestMapping("/sample/*")
@Controller
public class ControllerClass {

    @Autowired
    ServiceClass serviceClass;

    @RequestMapping(value = { "index" })
    @Transactional
    public String index(){
        serviceClass.updateDB();

        return "sample/index";
    }
}

ServiceClass.java

@Service
public class ServiceClass {

    public void updateDB() {
        //DB update process
    }
}

Also, the transaction works in the same way when the method is called by specifying the time by `` `@ Scheduled```.

ControllerClass.java

@Controller
public class ControllerClass {

    @Autowired
    ServiceClass serviceClass;

    @Scheduled(cron = "0 0 10 * * *")
    @Transactional
    public String index(){
        serviceClass.updateDB();

        return "sample/index";
    }
}

Implementation example

Considering a practical implementation, I want to roll back even if an exception other than RuntimeException occurs.

@Transactional(rollbackFor = Exception.class)Set Exception and classes that inherit Exception to be rolled back when thrown.

 Try-catch with the calling method and divide the process according to success or failure.


#### **`ControllerClass.java`**
```java

@RequestMapping("/sample/*")
@Controller
public class ControllerClass {

    @Autowired
    ServiceClass serviceClass;

    @RequestMapping(value = { "exec" })
    public String exec(Model model){

        try {
            //Calling a method that makes a transaction
            serviceClass.transaction();

            //What to do if successful
            model.addAttribute("message", "The process was successful.");
        } catch (Exception e) {
            //Processing when processing fails
            if (e.getMessage() != null) {
                 model.addAttribute("message", e.getMessage());
            } else {
                 model.addAttribute("message", "An error has occurred.");
            }
            return "sample/index";
        }
        return "sample/complete";
    }
}

ServiceClass.java

@Service
public class ServiceClass {

    @Transactional(rollbackFor = Exception.class)
    public void transaction() throws Exception {
        //A series of processes that you want to transaction
        //If you want to roll back, throw Exception as below
        throw new Exception("Processing failed.");
    }
}