关于java：Request，Session和ServletContext中的属性之间的差异


Differences between attributes in Request, Session and ServletContext

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我很难理解这三种设置属性的方法之间的区别：

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// String as attribute of request
req.setAttribute("name","Sluggo");

// Integer as attribute of session
req.getSession().setAttribute("age", 10);

// Date as attribute of context
getServletContext().setAttribute("today", new Date());
  • 有什么区别？
  • 你应该什么时候使用？
    • 相关讨论

    A ServletContext attribute is an object bound into a context
    through the ServletContext.setAttribute() method and which is
    available to ALL Servlets (thus JSP) in that context, or to other
    contexts via the getContext() method. By definition a context
    attribute exists locally in the VM where they were defined. So,
    they're unavailable on distributed applications.

    Session attributes are bound to a Session, as a mean to provide state to a set of related HTTP requests. Session attributes are
    available ONLY to those Servlets which join the session. They're also
    unavailable to different JVMs in distributed scenarios. Objects can be
    notified when they're bound/unbound to the Session implementing the
    HttpSessionBindingListener interface.

    Request attributes are bound to a specific request object, and they last as far as the request is resolved or while it keeps being
    dispatched from Servlet to Servlet. They're used more as communication
    channel between Servlets via the RequestDispatcher Interface (since
    you can't add Parameters...) and by the container. Request attributes
    are very useful in web apps when you must provide setup information
    between information providers and the information presentation layer
    (a JSP) that is bound to a specific request and need not be available
    any longer, which usually happens with sessions without a rigorous
    control strategy.

    IN SUMMARY, we can say that:

    • Context attributes are meant for infra-structure, such as shared connection pools.
    • Session attributes are meant for contextual information, such as user identification.
    • Request attributes are meant for specific request info, such as query results.

    来源：servlets访谈问题，作者：krishna [email protected]

    这三个具有不同的范围：

    • 请求属性在该请求/响应周期的生命周期内有效

    • 会话生命周期的会话属性

    • ServletContext跨越servlet上下文，它一直存在到上下文被破坏为止。

    相关讨论