Servlet之config的使用

不多说，直接上代码

LoginServlet.java

package web;

import java.io.IOException;

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 LoginServlet extends HttpServlet {

    
    //tomcat创建Servlet的逻辑:
    //LoginServlet s = new LoginServlet();
    //ServletConfig c = new ServletConfig();
    //c.加载数据();//从web.xml加载数据
    //s.init(c);
    @Override
    public void init(ServletConfig config) throws ServletException {
        
        super.init(config);
        String maxOnline = config.getInitParameter("maxOnline");
        System.out.println(maxOnline);
    }

    @Override
    protected void service(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
        //此config就是init()传入的那个
        ServletConfig cfg = getServletConfig();
        String maxOnline = cfg.getInitParameter("maxOnline");
        System.out.println(maxOnline);
        System.out.println("正在登陆...");
    }
    
}

xml

<servlet>
      <servlet-name>login</servlet-name>
      <servlet-class>web.LoginServlet</servlet-class>
      <!-- 给此Servlet预置参数 -->
      <init-param>
          <param-name>maxOnline</param-name>
          <param-value>3000</param-value>
      </init-param>
  </servlet>
  <servlet-mapping>
      <servlet-name>login</servlet-name>
      <url-pattern>/login</url-pattern>
  </servlet-mapping>