JavaWeb-----ServletConfig对象和servletContext对象

1.ServletConfig

ServletConfig:代表当前Servlet在web.xml中的配置信息

String getServletName() -- 获取当前Servlet在web.xml中配置的名字
String getInitParameter(String name) -- 获取当前Servlet指定名称的初始化参数的值
Enumeration getInitParameterNames() -- 获取当前Servlet所有初始化参数的名字组成的枚举
ServletContext getServletContext() -- 获取代表当前web应用的ServletContext对象

在Servlet的配置文件中，可以使用一个或多个<init-param>标签为servlet配置一些初始化参数

当servlet配置了初始化参数后，web容器在创建servlet实例对象时，会自动将这些初始化参数封装到ServletConfig对象中

配置Web.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_3_1.xsd"

    id="WebApp_ID" version="3.1">

    <display-name>Servlet_ServletConfig</display-name>

    <welcome-file-list>

        <welcome-file>index.jsp</welcome-file>

    </welcome-file-list>

    <servlet>

        <servlet-name>AchieveParam</servlet-name>

        <servlet-class>com.servlets.AchieveParamServlet</servlet-class>

        <init-param>

            <param-name>userName</param-name>

            <param-value>jtx</param-value>

        </init-param>

        <init-param>

            <param-name>userPwd</param-name>

            <param-value>123456</param-value>

        </init-param>

        <load-on-startup>1</load-on-startup>

    </servlet>

    <servlet-mapping>

        <servlet-name>AchieveParam</servlet-name>

        <url-pattern>*.do</url-pattern>

    </servlet-mapping>

</web-app>

Servlet处理类

package com.servlets;

import java.io.IOException;

import java.util.Enumeration;

import javax.servlet.ServletConfig;

import javax.servlet.ServletContext;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import javax.servlet.http.HttpSession;

/**

 * 可以实现Servlet接口

 *

 * @author yyx 2019年3月13日

 */

public class AchieveParamServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    @Override

    protected void service(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        // 设置输出内容的编码方式

        response.setCharacterEncoding("UTF-8");

        // 获得Session

        HttpSession httpSession = request.getSession();

        // 获得ServletConfig对象

        ServletConfig servletConfig = this.getServletConfig();

        String userName = servletConfig.getInitParameter("userName");

        String userPwd = servletConfig.getInitParameter("userPwd");

        httpSession.setAttribute("userName", userName);

        httpSession.setAttribute("userPwd", userPwd);

        /*

         * getServletName()获取当前Servlet在web.xml中配置的名字

         * getServletContext()获取代表当前web应用的ServletContext对象

         * getInitParameterNames()获取当前Servlet所有初始化参数的名字组成的枚举

         */

        System.out.println(servletConfig.getServletName());

        ServletContext sContext = servletConfig.getServletContext();

        Enumeration<String> enumeration = servletConfig.getInitParameterNames();

        while (enumeration.hasMoreElements()) {

            String name= enumeration.nextElement();
            String value = servletConfig.getInitParameter(name);

            System.out.println(value);

        }

        // 转发

        request.getRequestDispatcher("/success.jsp").forward(request, response);

    }

    @Override

    public void destroy() {

        super.destroy();

        System.out.println("Servlet销毁");

    }

    @Override

    public void init(ServletConfig config) throws ServletException {

        super.init(config);

        System.out.println("Servlet初始化");

    }

}

JSP页面

<%@ page language="java" contentType="text/html; charset=UTF-8"

    pageEncoding="UTF-8"%>

<!DOCTYPE html>

<html>

<head>

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

<title>Insert title here</title>

</head>

<body>

   <a href="${pageContext.request.contextPath}/achieveparamservlet.do">获取参数</a>

</body>

</html>

<%@ page language="java" contentType="text/html; charset=UTF-8"

    pageEncoding="UTF-8"%>

<!DOCTYPE html>

<html>

<head>

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

<title>Insert title here</title>

</head>

<body>

  <h2>${ userName}</h2>

  <h2>${ userPwd}</h2>

</body>

</html>

2.ServletContext

ServletContext官方叫servlet上下文

WEB容器在启动时，它会为每个WEB应用程序都创建一个对应的ServletContext对象，它代表当前web应用

是一个域对象
可以读取全局配置参数
可以搜索当前工程目录下面的资源文件
可以获取当前工程名字