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

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>
    <context-param>
        <param-name>company</param-name>
        <param-value>Alibaba</param-value>
    </context-param>
    <servlet>
        <servlet-name>AchieveParam</servlet-name>
        <servlet-class>com.servlets.AchieveParamServlet</servlet-class>

        <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.io.InputStream;
import java.util.Enumeration;
import java.util.Properties;

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;
    private int count;

    @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ServletContext对象，读取全局参数
        ServletContext servletContext = this.getServletContext();
        String company = servletContext.getInitParameter("company");
        httpSession.setAttribute("company", company);

        Enumeration<String> names = servletContext.getInitParameterNames();
        while (names.hasMoreElements()) {
            String name = names.nextElement();
            String value = servletContext.getInitParameter(name);
            System.out.println(value);
        }

        // web应用范围内共享数据,每调用一次方法都会加1
        servletContext.setAttribute("count", count++);

        // 读取配置文件
        InputStream is = servletContext.getResourceAsStream("/WEB-INF/classes/jdbc.properties");
        Properties properties = new Properties();
        properties.load(is);
        System.out.println(properties.getProperty("driverClass"));
        System.out.println(properties.getProperty("url"));
        is.close();

        // 获取工程名称
        System.out.println(servletContext.getContextPath());
        // 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="${pageContext.request.contextPath}/achieveparamservlet.do">获取参数</a>
</body>
</html>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
  <h2>${ company}</h2>
  <h2>${ count}</h2>
</body>
</html>
【推广】 免费学中医，健康全家人
原文地址：https://www.cnblogs.com/fengfuwanliu/p/10518467.html