As per the current trend, I can see from Juniors to Seniors all are using Spring boot as a weapon to build software. Why that should not be, it is developer friendly and its "convention over configuration" style helps the developer to only focus on business logic If they are ignorant how Springs works still just seeing a Spring boot tutorial one can start using Spring boot.
I like that one, at least major taskforce in support project is now being utilized as they do not have to know Spring inner details, just put some annotations and write the business code and voila, with that said sometimes in some cases you have to know "How it works", what I am trying to say, you need to know your tool better then only you can utilize your tool as a PRO.
In this Article, I will give you an idea of how you can use asynchronous processing in Spring.
Any pieces of logic, which is not directly associated with business logic (Cross-cutting concerns) or a logic whose response not needed in invoker context to determine next flow or any business computation is an ideal candidate of Asyncronization. Also Integrating two distributed system Asyncronization technique is being used to make them decoupled.
In Spring we can use Asynchronization using @Async annotation, but wait here if you use randomly @Async annotation on top of a method and think your method will be invoked as a asynchronous fashion in a separate thread you are wrong. you need to know How @Async works and it's limitations, without that you can't understand Async behavior.
How @Async Works?
When you put an @Async annotation on a method, underlying it creates a proxy of that object where @Async is defined (JDK Proxy/CGlib) based on the proxyTargetClass property. then Spring tries to find a thread pool associated with the context, to submit this method's logic as a separate path of execution to be exact it searches a unique TaskExecutor bean or a bean named as taskExecutor if not found then use default SimpleAsyncTaskExecutor.
Now, as it creates a proxy and submits the job to TaskExecutor thread pool, it has few limitations which you must have to know, otherwise, you will scratch your head why your Async is not worked or create a new thread!!!
Limitations of @Async
1. Suppose you write a class and identify a method which will act as Async and put @Async on top of that method, now if you want to use that class from another class by creating local instance then it will not fire the async, It has to be picked up by Spring @ComponentScan annotation or created inside a class marked as @Configuration.
Async Annotation use in a Class
package com.example.ask2shamik.springAsync.demo;
import java.util.Map;
import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Component;
@Component
public class AsyncMailTrigger {
@Async
public void senMail(Map<String,String> properties) {
System.out.println("Trigger mail in a New Thread :: " + Thread.currentThread().getName());
properties.forEach((K,V)->System.out.println("Key::" + K + " Value ::" + V));
}
}
Caller Class
package com.example.ask2shamik.springAsync.demo;
import java.util.HashMap;
import java.util.Map;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
@Component
public class AsyncCaller {
@Autowired
AsyncMailTrigger asyncMailTriggerObject;
public void rightWayToCall() {
System.out.println("Calling From rightWayToCall Thread " + Thread.currentThread().getName());
asyncMailTriggerObject.senMail(populateMap());
}
public void wrongWayToCall() {
System.out.println("Calling From wrongWayToCall Thread " + Thread.currentThread().getName());
AsyncMailTrigger asyncMailTriggerObject = new AsyncMailTrigger();
asyncMailTriggerObject.senMail(populateMap());
}
private Map<String,String> populateMap(){
Map<String,String> mailMap= new HashMap<String,String>();
mailMap.put("body", "A Ask2Shamik Article");
return mailMap;
}
}
Here I create two methods one use the @Autowired version of AsyncMailtrigger, which will be picked by @ComponentScan but in a WrongWayTo Call method I create the object in local so it will not be picked up by @ComponentScan hence not spawn a new thread it executed inside the main thread.
Outcome
Calling From rightWayToCall Thread main
2019-03-09 14:08:28.893 INFO 8468 --- [ main] o.s.s.concurrent.ThreadPoolTaskExecutor : Initializing ExecutorService 'applicationTaskExecutor'
Trigger mail in a New Thread :: task-1
Key::body Value ::A Ask2Shamik Article
++++++++++++++++
Calling From wrongWayToCall Thread main
Trigger mail in a New Thread :: main
Key::body Value ::A Ask2Shamik Article
2. Never use @Async on top of a private method as in runtime it will not able to create a proxy, so not working.
@Async
private void senMail() {
System.out.println("A proxy on Private method " + Thread.currentThread().getName());
}
3. Never writes Async method in the same class where caller method invokes the same Async method , so always remember using this reference Async not worked, because in this case,although it creates a proxy but this call bypass the proxy and call directly the method so Thread will not be spawned and developer in a wrong assumption that, it will work like async fashion, Most developers implement async in this way carelessly, so be very careful while writing Async, Caller method should be in different class, while calling Async method.
Example
package com.example.ask2shamik.springAsync.demo;
import java.util.HashMap;
import java.util.Map;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Component;
@Component
public class AsyncCaller {
@Autowired
AsyncMailTrigger asyncMailTriggerObject;
public void rightWayToCall() {
System.out.println("Calling From rightWayToCall Thread " + Thread.currentThread().getName());
asyncMailTriggerObject.senMail(populateMap());
}
public void wrongWayToCall() {
System.out.println("Calling From wrongWayToCall Thread " + Thread.currentThread().getName());
this.senMail(populateMap());
}
private Map<String,String> populateMap(){
Map<String,String> mailMap= new HashMap<String,String>();
mailMap.put("body", "A Ask2Shamik Article");
return mailMap;
}
@Async
public void senMail(Map<String,String> properties) {
System.out.println("Trigger mail in a New Thread :: " + Thread.currentThread().getName());
properties.forEach((K,V)->System.out.println("Key::" + K + " Value ::" + V));
}
}
The last piece is to execute the application, please note we use @EnableAsync annotation, by this Spring submits @Async methods in a background thread pool. This class can customize, the used Executor by defining a new bean, I will discuss it in later with an Example How to do that.
package com.example.ask2shamik.springAsync;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.scheduling.annotation.EnableAsync;
import com.example.ask2shamik.springAsync.demo.AsyncCaller;
@SpringBootApplication
@EnableAsync
public class DemoApplication {
@Autowired
AsyncCaller caller;
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
@Bean
public CommandLineRunner commandLineRunner(ApplicationContext ctx) {
return args -> {
caller.rightWayToCall();
Thread.sleep(1000);
System.out.println("++++++++++++++++");
Thread.sleep(1000);
caller.wrongWayToCall();
};
}
}
Conclusion: Hope now you are able to understand How Async works internally and its limitation, now in next Article I will discuss on Exception handler in Async.
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