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Bean Scope
| scope | description | - |
|---|---|---|
| singletion | (Default) Scopes a single bean definition to a single object instance per Spring IoC container. | 单例bean |
| prototype | Scopes a single bean definition to any number of object instances. | 多例bean,每次请求都新产生bean |
| request | Scopes a single bean definition to the lifecycle of a single HTTP request; that is, each HTTP request has its own instance of a bean created off the back of a single bean definition. Only valid in the context of a web-aware Spring ApplicationContext. | 每一次HTTP请求都会产生一个新的bean，该bean仅在当前HTTP request内有效 |
| session | Scopes a single bean definition to the lifecycle of an HTTP Session. Only valid in the context of a web-aware Spring ApplicationContext. | 每一次HTTP请求都会产生一个新的 bean，该bean仅在当前 HTTP session 内有效 |
| application | Scopes a single bean definition to the lifecycle of a ServletContext. Only valid in the context of a web-aware Spring ApplicationContext. | - |
| websocket | Scopes a single bean definition to the lifecycle of a WebSocket. Only valid in the context of a web-aware Spring ApplicationContext. | - |
Spring bean 的默认作用范围是什么？
singletion
Spring 中的 singleton bean 的线程安全问题？
存在线程问题;
对于一个无状态Bean(即对bean属，性只有读操作，无写操作)，那么这个单例Bean是线程安全的。比如Spring mvc 的 Controller、Service、Dao等，这些Bean大多是无状态的，只关注于方法本身。
对于有状态的bean，Spring官方提供的bean，一般提供了通过
ThreadLocal去解决线程安全的方法，比如RequestContextHolder、TransactionSynchronizationManager、LocaleContextHolder等。
prototype
- Spring does not manage the complete lifecycle of a prototype bean
@Component("userService")
@Scope("prototype")
public class UserServiceImpl implements UserService {
@Autowired
private UserRepo userRepo;
@Override
public User getUserById(Integer id){
User user = userRepo.getById(id);
try {
TimeUnit.SECONDS.sleep(2);
} catch (Exception e) {
e.printStackTrace();
}
return user;
}
}
- AbstractBeanFactory类的
doGetBean方法
else if (mbd.isPrototype()) {
// It's a prototype -> create a new instance.
Object prototypeInstance = null;
try {
beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
总结：多线程, 生成多个实例，Ioc容器不负责完整的生命周期