Spring-Controller的范围及其实例变量 [英] Scope of a Spring-Controller and its instance-variables

问题描述

Spring-MVC中的所有控制器是否都是单例的，并且在不同的会话和请求之间共享?

Are all controllers in Spring-MVC singletons and are shared among different sessions and requests?

如果是这样，我认为像这样的类变量

If so, I assume that a class-variable like

public String name;

所有请求和会话都相同吗?这样，如果用户X发出请求并将name设置为 Paul ，那么用户Z还将Paul作为属性吗?

would be the same for all requests and sessions? So that if User X makes a request and name is being set to Paul, User Z also has Paul as attribute?

在我的情况下，我不希望这种行为，但想知道是否有比session.getAttribute()/request.getAttribute()

In my case I do NOT want that behaviour but wondered if there is a more easier, or more cleaner OOP-way to have session/request-variables then session.getAttribute()/request.getAttribute()

推荐答案

回答第一个问题:是的，Spring MVC控制器默认为单例.对象字段将为所有请求和所有会话永久共享并可见.

To answer your first question: yes, Spring MVC controllers are singletons by default. An object field will be shared and visible for all requests and all sessions forever.

但是，如果不进行任何同步，则可能会遇到各种各样的并发问题(竞争条件，可见性).因此，您的字段应该具有volatile(顺便说一下，还有private)修饰符，以避免可见性问题.

However without any synchronization you might run into all sorts of concurrency issues (race conditions, visibility). Thus your field should have volatile (and private, by the way) modifier to avoid visibility issues.

回到您的主要问题:在Spring中，您可以使用 request-(请参阅 4.5.4.3会话范围 )豆.您可以将它们注入控制器和任何其他bean(甚至是单例！)，但是Spring确保每个请求/会话都有一个独立的实例.

Back to your main question: in Spring you can use request- (see 4.5.4.2 Request scope) and session-scoped (see: 4.5.4.3 Session scope) beans. You can inject them to controllers and any other beans (even singletons!), but Spring makes sure each request/session has an independent instance.

将请求和会话范围的bean注入单例时，要记住的是将它们包装在作用域代理中(示例取自

Only thing to remember when injecting request- and session-scoped beans into singletons is to wrap them in scoped proxy (example taken from 4.5.4.5 Scoped beans as dependencies):

<!-- an HTTP Session-scoped bean exposed as a proxy -->
<bean id="userPreferences" class="com.foo.UserPreferences" scope="session">

    <!-- instructs the container to proxy the surrounding bean -->
    <aop:scoped-proxy/>
</bean>

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