Servlet自启动

有时候要执行一些初始化的代码，比如校验数据库的完整性，就需要自启动

load-on-startup

• 在web.xml中增加一句：<load-on-startup>10</load-on-startup>

• 10表示优先级，数字越小，启动的优先级越高

  
  image.png

• web.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<web-app>

    <servlet>
        <servlet-name>HelloServlet</servlet-name>
        <servlet-class>HelloServlet</servlet-class>
        <load-on-startup>10</load-on-startup>
    </servlet>
    
    <servlet-mapping>
        <servlet-name>HelloServlet</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>
    
    <servlet>
        <servlet-name>LoginServlet</servlet-name>
        <servlet-class>LoginServlet</servlet-class>
    </servlet>
    
    <servlet-mapping>
        <servlet-name>LoginServlet</servlet-name>
        <url-pattern>/login</url-pattern>
    </servlet-mapping>
    
</web-app>

• HelloServlet.java文件

import java.io.IOException;
import java.util.Date;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class HelloServlet extends HttpServlet {
    
    @Override
    public void init(ServletConfig config) throws ServletException {
        System.out.println("init of Hello Servlet");
    }
    
    public void doGet(HttpServletRequest request, HttpServletResponse responce) {
        // TODO Auto-generated method stub
        try {
            responce.getWriter().println("<h1>Hello Servlet!</h1>");
            responce.getWriter().println(new Date().toLocaleString());
        } catch (Exception e) {
            // TODO: handle exception
            e.printStackTrace();
        }
    }
}