Are beans in spring thread-safe?

Are beans in spring thread-safe?

#Spring does not guarantee bean thread safety.

By default, beans in the spring container are singletons. When there is a race condition in a singleton, there is a thread safety issue. As the example below

Counting class

package constxiong.interview.threadsafe;
 
/**
 * 计数类
 * @author ConstXiong
 * @date 2019-07-16 14:35:40
 */
public class Counter {
 
	private int count = 0;
	
	public void addAndPrint() {
		try {
			Thread.sleep(10);
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		System.out.println(++count);
	}
}

spring configuration file

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:context="http://www.springframework.org/schema/context"
	xsi:schemaLocation="
		http://www.springframework.org/schema/beans 
		http://www.springframework.org/schema/beans/spring-beans.xsd
	    http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd">
        
	<bean id="counter" class="constxiong.interview.threadsafe.Counter" />
	
</beans>

Test class

package constxiong.interview.threadsafe;
 
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
 
public class CounterTest {
	
	public static void main(String[] args) {
		final ApplicationContext context = new ClassPathXmlApplicationContext("spring_safe.xml");
 
		for (int i = 0; i < 10; i++) {
			new Thread(){
				@Override
				public void run() {
					Counter counter = (Counter)context.getBean("counter");
					for (int j = 0; j < 1000; j++) {
						counter.addAndPrint();
					}
				}
			}.start();
		}
		
	}
	
}

Print the beginning and end of the result

1
5
7
4
2
6
3
8
9
.
.
.
9818
9819
9820
9821
9822
9823
9824
9825

The maximum value expected to be printed should be 10000

Modify the spring configuration file and change the bean scope to prototype

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:context="http://www.springframework.org/schema/context"
	xsi:schemaLocation="
		http://www.springframework.org/schema/beans 
		http://www.springframework.org/schema/beans/spring-beans.xsd
	    http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd">
	<bean id="counter" class="constxiong.interview.threadsafe.Counter" scope="prototype"/>
</beans>

The test result outputs 10 1000

That is, each thread creates a Counter object and counts independently within the thread, so there is no thread safety issue. But this is not the result we want, 10000 is printed.

So the thread safety of beans managed by spring is related to whether there are race conditions in the creation scope of the bean and the usage environment where the bean is located. Spring cannot guarantee the thread safety of beans.

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