spring - 用NEW创建的spring bean真的是单例吗

Question

我在这样的配置类中创建了一个spring bean:

@Bean
MyClass getMyClass() {
    MyClass mc = new MyClass()
    return mc;
}

每当MyClass在另一个需要注入(inject)的类中 Autowiring ，它是否总是会根据 new 创建一个新对象？在bean定义中？
以这种方式创建的 bean 是真正的单例吗？

Answer 1

Spring保证您在使用 Bean 注释的方法中所做的任何事情注释它只会做一次。内部 Spring 工厂会处理这个问题。

当然，这取决于 scope但默认范围是 singleton .请参阅文档:

Scopes

Bean

Is spring default scope singleton or not?

小例子应该可以帮助您了解它是如何工作的:

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import java.time.LocalDateTime;
import java.util.Random;

@Configuration
public class SpringApp {

    public static void main(String[] args) {
        ApplicationContext ctx = new AnnotationConfigApplicationContext(SpringApp.class);

        System.out.println(ctx.getBean(MyClass.class));
        System.out.println(ctx.getBean(MyClass.class));
        System.out.println(ctx.getBean(MyClass.class));
        System.out.println(ctx.getBean(MyClass.class));
    }

    @Bean
    public MyClass getMyClass() {
        System.out.println("Create instance of MyClass at " + LocalDateTime.now());
        MyClass myClass = new MyClass();

        return myClass;
    }
}

class MyClass {

    private int value = new Random().nextInt();

    @Override
    public String toString() {
        return super.toString() + " with values = " + value;
    }
}

打印:

Create instance of MyClass at 2019-01-09T22:54:37.025
com.celoxity.spring.MyClass@32a068d1 with values = -1518464221
com.celoxity.spring.MyClass@32a068d1 with values = -1518464221
com.celoxity.spring.MyClass@32a068d1 with values = -1518464221
com.celoxity.spring.MyClass@32a068d1 with values = -1518464221

当您定义具有范围 protoype 的 bean 时

@Scope("prototype")
@Bean
public MyClass getMyClass()

应用程序打印:

Create instance of MyClass at 2019-01-09T22:57:12.585
com.celoxity.spring.MyClass@282003e1 with values = -677868705
Create instance of MyClass at 2019-01-09T22:57:12.587
com.celoxity.spring.MyClass@7fad8c79 with values = 18948996
Create instance of MyClass at 2019-01-09T22:57:12.587
com.celoxity.spring.MyClass@71a794e5 with values = 358780038
Create instance of MyClass at 2019-01-09T22:57:12.587
com.celoxity.spring.MyClass@76329302 with values = 868257220