Servlet方法生命周期及执行原理详解

public class ServletDemo1 implements Servlet {
    /**
     * 初始化方法
     * 在Servlet被创建时，执行。只会执行一次
     * @param servletConfig
     * @throws ServletException
     * */
    @Override
    public void init(ServletConfig servletConfig) throws ServletException {
        System.out.println("init......");
    }
    /**
     * 获取ServletConfig对象
     * ServletCongig:Servlet的配置对象
     * @return
     * */
    @Override
    public ServletConfig getServletConfig() {
        return null;
    }
    /**
     * 提供服务方法
     * 每一次Servlet被访问时，执行。可执行多次
     * @param servletRequest
     * @param servletResponse
     * @throws ServletException
     * @throws IOException
     * */
    @Override
    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
        System.out.println("服务小皮皮美滋滋！");
    }
    /**
     * 获取Servlet的一些详细，版本，作者等等
     * @return 
     * */
    @Override
    public String getServletInfo() {
        return null;
    }
    /**
     * 销毁方法
     * 在服务器正常关闭时执行。执行一次
     * */
    @Override
    public void destroy() {
        System.out.println("服务关闭了...");
    }
}

<!--配置Servlet -->
    <servlet>
        <servlet-name>demo1</servlet-name>
        <servlet-class>xppmzz.ServletDemo1</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>demo1</servlet-name>
        <url-pattern>/demo1</url-pattern>
    </servlet-mapping>

  <servlet>
        <servlet-name>demo1</servlet-name>
        <servlet-class>xppmzz.ServletDemo1</servlet-class>
        <load-on-startup>5</load-on-startup>
  </servlet>

			@Target({ElementType.TYPE})
			@Retention(RetentionPolicy.RUNTIME)
			@Documented
			public @interface WebServlet {
			    String name() default "";//相当于<Servlet-name>
			
			    String[] value() default {};//代表urlPatterns()属性配置
			
			    String[] urlPatterns() default {};//相当于<url-pattern>
			
			    int loadOnStartup() default -1;//相当于<load-on-startup>
			
			    WebInitParam[] initParams() default {};
			
			    boolean asyncSupported() default false;
			
			    String smallIcon() default "";
			
			    String largeIcon() default "";
			
			    String description() default "";
			
			    String displayName() default "";
			}

@WebServlet("/demo2")
public class ServletDemo2 extends GenericServlet {
    @Override
    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
        System.out.println("GenericServlet....");
    }
}

@WebServlet("/demo3")
public class ServletDemo3 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("doGet......");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("doPost......");
    }
}