Spring父容器与Spring MVC子容器是如何体现出父子关系的

Question

平常的子类继承父类通过extends关键字来实现,那么Spring父容器与Spring MVC子容器是如何体现出父子关系的呢?
容器指的是一个类吗?Spring容器是哪个类，Spring MVC容器又是哪个类?

Answer 1

所谓容器，就是上下文，在这同一个上下文里，大家可以共享一些东西。

在Spring应用启动时，会先读取web.xml文件，调用ContextLoaderListener创建Spring容器，也就是你说的父容器。

    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>

Listener创建完之后，开始创建Servlet：

    <servlet>
        <servlet-name>SpringMVC</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    </servlet>

这时候这个DispatcherServlet开始试图创建SpringMVC的ApplicationContext，它先找刚才由上面那个ContextLoaderListener创建的Spring的ApplicationContext，找到后，把Spring的ApplicationContext作为参数传给DispatcherServlet的ApplicationContext的setParent方法，这样SpringMVC的容器就变成了Spring容器的儿子。

因为在SpringMVC这个子容器创建的时候指定了它的Spring父容器，所以儿子能找到父亲，所以SpringMVC这个子容器里的Bean可以调用父容器的服务，而父容器不知道有这个儿子的存在（一个不负责任的父亲），父容器里的Bean不能调用子容器里的服务。

Answer 2

想必Servlet的关系就不必多说了，直接上代码吧
HttpServletBean 继承了 HttpServlet，init方法如下

    @Override
    public final void init() throws ServletException {
        // Let subclasses do whatever initialization they like.
        initServletBean();
    }

看看子类FrameworkServlet#initServletBean 方法

@Override
protected final void initServletBean() throws ServletException {
    this.webApplicationContext = initWebApplicationContext();
    initFrameworkServlet();
}

看看 initWebApplicationContext

protected WebApplicationContext initWebApplicationContext() {
        WebApplicationContext rootContext =WebApplicationContextUtils.getWebApplicationContext(getServletContext());
        WebApplicationContext wac = null;

        if (this.webApplicationContext != null) {
            wac = this.webApplicationContext;
            if (wac instanceof ConfigurableWebApplicationContext) {
                ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
                if (!cwac.isActive()) {
                    // The context has not yet been refreshed -> provide services such as
                    // setting the parent context, setting the application context id, etc
                    if (cwac.getParent() == null) {
                        // The context instance was injected without an explicit parent -> set
                        // the root application context (if any; may be null) as the parent ,看到没有，如果有就设置rootApplicationContext,
                        cwac.setParent(rootContext);
                    }
                    configureAndRefreshWebApplicationContext(cwac);
                }
            }
        }
        if (wac == null) {
            // No context instance was injected at construction time -> see if one
            // has been registered in the servlet context. If one exists, it is assumed
            // that the parent context (if any) has already been set and that the
            // user has performed any initialization such as setting the context id
            wac = findWebApplicationContext();
        }
        if (wac == null) {
            // No context instance is defined for this servlet -> create a local one
            wac = createWebApplicationContext(rootContext);
        }

        if (!this.refreshEventReceived) {
            // Either the context is not a ConfigurableApplicationContext with refresh
            // support or the context injected at construction time had already been
            // refreshed -> trigger initial onRefresh manually here. 看到这里就不多说了，初始化beanFactory
            onRefresh(wac);
        }

        if (this.publishContext) {
            String attrName = getServletContextAttributeName();
            getServletContext().setAttribute(attrName, wac);
        }

        return wac;
    }

结束，就是辣么简单

Answer 3

https://blog.csdn.net/wuseyuk...

Answer 4

不是很清楚

哈哈哈不好意思，我就是来找这个问题的答案的。