JavaWeb之Servlet（三）ServletConfig与ServletContext

导航

·JavaWeb之Servlet（一）Maven创建Servlet项目时的换源与运行时404的可能解决方案
·JavaWeb之Servlet（二）Servlet生命周期方法与GET/POST请求分发
·JavaWeb之Servlet（三）ServletConfig与ServletContext
·JavaWeb之Servlet（四）HttpServletRequest与HttpServletResponse

前言

–>视频教程传送门<–

项目结构：

一、ServletConfig

Ⅰ、创建ServletConfig类对象

ServletConfig类是配置文件，通过方法getServletConfig()得到ServletConfig类对象

ServletConfig config = getServletConfig();

Ⅱ、ServletConfig类对象方法

方法	描述
ServletConfig.getServletName()	获取当前程序的名称
ServletConfig.getServletContext()	获取web.xml初始化配置的参数
ServletConfig.getInitParameter(String)	获取servletContext

参数只能由当前程序访问

Ⅲ、java程序

package com.HolaAs;

import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class configServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletConfig config = getServletConfig();

        System.out.println("Name: "+ config.getServletName());
        System.out.println("context: "+ config.getServletContext());
        System.out.println("init-param: "+ config.getInitParameter("password"));

    }
}

Ⅳ、配置web.xml

<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>

  <servlet>
    <servlet-name>configServlet</servlet-name>
    <servlet-class>com.HolaAs.configServlet</servlet-class>
    //配置初始化参数,可重复多次
    <init-param>
      <param-name>password</param-name>
      <param-value>1234</param-value>
    </init-param>
  </servlet>

  <servlet-mapping>
    <servlet-name>configServlet</servlet-name>
    <url-pattern>/config</url-pattern>
  </servlet-mapping>

</web-app>

Ⅴ、回显

二、ServletContext

Ⅰ、创建ServletContext类对象

ServletContext类是上下文，通过方法getServletContext()得到ServletContext类对象

ServletContext context = getServletContext();

Ⅱ、ServletContext类对象方法

方法	描述
ServletContext.getInitParameter(String)	获取上下文参数
ServletContext.getContextPath()	获取工程路径
ServletContext.getRealPath("/")	获取在服务器端的绝对路径
ServletContext.setAttribute(String key,String value)	添加域数据
ServletContext.getAttribute(String key)	获取域数据
ServletContext.removeAttribute(String key)	删除域数据

上下文参数在Servlet初始化的时候创建，在Servlet关闭的时候回收
全部程序均可访问

Ⅲ、java程序

package com.HolaAs;

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 java.io.IOException;

public class contextServlet1 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        ServletContext context = getServletContext();

        System.out.println("context-param: "+context.getInitParameter("username"));
        System.out.println("Project path: "+context.getContextPath());
        System.out.println("In-disk path: "+context.getRealPath("/"));
        
        context.setAttribute("key1","value1");
        System.out.println("getValue: "+context.getAttribute("key1"));

    }

}

Ⅳ、配置web.xml

<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
  //配置上下文参数
  <context-param>
    <param-name>username</param-name>
    <param-value>root</param-value>
  </context-param>
  
  <servlet>
    <servlet-name>contextServlet</servlet-name>
    <servlet-class>com.HolaAs.contextServlet</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>contextServlet</servlet-name>
    <url-pattern>/context</url-pattern>
  </servlet-mapping>

</web-app>

Ⅴ、回显

完

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