javaWeb 获得servelt初始化参数以及config为null的问题

喜欢ヅ旅行 2023-06-19 09:33 19阅读 0赞

注意：如果是3.0以上Tomcat，具有注释配置的功能，

这时如果@WebServlet("/HelloServlet")，即在注解中声明一个servelt

然后你又憨憨的在web.xml中声明了一遍，并且在xml中声明了servelt初始化变量。

放心，你访问不到初始化变量。

因为你只能通过注解的那种方式访问，但是注解中你没有声明变量，所以：

要么把参数声明转移到注解，要么删除注解。

package com.my.servlet;
    
    import java.io.IOException;
    import java.io.PrintWriter;
    
    import javax.servlet.ServletConfig;
    import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    /**
     * Servlet implementation class HelloServlet
     */
    //@WebServlet("/HelloServlet")这是那行万恶的注解
    public class HelloServlet extends HttpServlet {
    	private static final long serialVersionUID = 1L;
           
    	
    	/**
         * @see HttpServlet#HttpServlet()
         */
        public HelloServlet() {
            super();
        }
        public void init(ServletConfig config) throws ServletException{
        	super.init(config);
        	System.out.println(this.getClass().getName()+"的init方法被调用:");
        	
        }
        
        public void destroy() {
        	System.out.println(this.getClass().getName()+"的destory方法被调用");
        }
    	/**
    	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
    	 */
    	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		ServletConfig config=getServletConfig();
        	String url = config.getInitParameter("password");
        	System.out.println(url);
    	}
    
    	/**
    	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
    	 */
    	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    	}
    
    }

xml

<?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xmlns="http://xmlns.jcp.org/xml/ns/javaee" 
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" 
    id="WebApp_ID" version="4.0">
      <display-name>mytest2</display-name>
      <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.htm</welcome-file>
        <welcome-file>index.jsp</welcome-file>
        <welcome-file>default.html</welcome-file>
        <welcome-file>default.htm</welcome-file>
        <welcome-file>default.jsp</welcome-file>
      </welcome-file-list>
      <servlet>
    	<servlet-name>HelloServlet</servlet-name>
    	<servlet-class>com.my.servlet.HelloServlet</servlet-class>
    	<init-param>
    		<param-name>url</param-name>
    		<param-value>ifyouwannago</param-value>
    	</init-param>
    	<init-param>
    		<param-name>user</param-name>
    		<param-value>qst</param-value>
    	</init-param>
    	<init-param>
    		<param-name>password</param-name>
    		<param-value>qst123</param-value>
    	</init-param>
    </servlet>
    
    <servlet-mapping>
    	<servlet-name>HelloServlet</servlet-name>
    	<url-pattern>/</url-pattern>
    </servlet-mapping>
      
    </web-app>