菜鸟学习 Spring 之 DispatcherServlet

2019-04-27 本文已影响0人醉疯觞

写在前面

关于 DispatcherServlet 已经有很多博客，这里可以说是一篇整理文章然后加了一些自己的理解。
说到 DispatcherServlet 就不得不提到 Servlet，所以下面主要讲讲 Servlet

Servlet 生命周期

关于 Servlet 周期，这里结合源码注释进行说明：

package javax.servlet;

public interface Servlet {

    /**
     * The servlet container calls the <code>init</code> method exactly once
     * after instantiating the servlet. The <code>init</code> method must
     * complete successfully before the servlet can receive any requests.
     * 
     *  大意就是 servlet 容器会在实例化时调用一次（仅此一次）init 方法
     *  调用完成后才可以接收请求
     *
     */
    public void init(ServletConfig config) throws ServletException;

    /**
     * Called by the servlet container to allow the servlet to respond to a
     * request.
     *  
     * 
     * This method is only called after the servlet's <code>init()</code> method
     * has completed successfully.
     * 
     *  servlet 容器调用 service 方法响应请求，并且该方法只能在 init 方法调用成功后才能被调用。
     * 
     */
    public void service(ServletRequest req, ServletResponse res)
            throws ServletException, IOException;


    /**
     * Called by the servlet container to indicate to a servlet that the servlet
     * is being taken out of service. This method is only called once all
     * threads within the servlet's <code>service</code> method have exited or
     * after a timeout period has passed. After the servlet container calls this
     * method, it will not call the <code>service</code> method again on this
     * servlet.
     *
     *  
     * 大意就是说，这个方法被调用后，会等待容器内所有线程执行 service 方法完毕
     * 或超时（并且容器不会再接收请求调用 service 方法），才执行方法内容。
     * 
     */
    public void destroy();
    
    public ServletConfig getServletConfig();

    public String getServletInfo();
}

由源码可知，Servlet 生命周期：