servlet 服務器啓動Init

servlet生命週期：服務器啓動構造器創建之後，一直到服務器關閉destory

默認當服務器啓動就init Servlet需要配置：（兩種方式）

1：web.xml文件中添加<load-on-startup>1</load-on-startup> 

<?xml version="1.0" encoding="utf-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
                      http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
  version="3.0" metadata-complete="true">
 
	<servlet>
		<servlet-name>HelloServlet</servlet-name>
		<servlet-class>com.zhengqing._01Helloservlet.HelloServlet</servlet-class>
		<load-on-startup>1</load-on-startup>
	</servlet>
	<servlet-mapping>
		<servlet-name>HelloServlet</servlet-name>
		<url-pattern>/HelloServlet</url-pattern>
	</servlet-mapping> 
 
</web-app>

2：註解 @WebServlet(value={"/HelloServlet"},loadOnStartup=1)

@WebServlet(value={"/HelloServlet"},loadOnStartup=1)
public class HelloServlet extends HttpServlet {
	@Override
	public void init() throws ServletException {
		System.out.println("===初始化===");
	}
	@Override
	protected void service(HttpServletRequest arg0, HttpServletResponse arg1) throws ServletException, IOException {
		System.out.println("===Servlet程序===");
	}
}

否則它的生命週期爲Servlet第一次被調用然後一直到服務器destory