1. ServletContext物件（域物件）    （*****）

1.1 定義：

WEB容器在啟動時，它會為每個WEB應用程式都建立一個對應的ServletContext物件，它代表當前web應用。

            一個WEB應用對應一個ServletContext物件

            一個WEB應用下有多個Servlet程式

            所有的servlet程式都共享同一個ServletContext物件

            demo1存入內容    ServletContext    demo2中取出來

2.作用：

2.1獲取WEB應用全域性初始化引數

                    * 在web.xml中配置
                        <context-param>
                            <param-name>encoding</param-name>
                            <param-value>UTF-8</param-value>
                        </context-param>
                    
                    String getInitParameter(String name)

                    getInitParameterNames()          

package cn.itcast.context;

import java.io.IOException;
import java.util.Enumeration;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


/**
 * 獲取全域性初始化引數
 * @author Administrator
 *
 */
public class ContextDemo1 extends HttpServlet {

	@SuppressWarnings("unchecked")
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		//獲取servletcontext物件
		ServletContext context = getServletContext();
		//獲取初始化引數
		String encoding = context.getInitParameter("encoding");
		System.out.println("編碼：" + encoding);
		
		Enumeration<String> e = context.getInitParameterNames();
		while(e.hasMoreElements()){
			String name = e.nextElement();
			String value = context.getInitParameter(name);
			System.out.println(name + ": " + value);
		}
		
		
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		doGet(request, response);
	}

}
 

2.2實現資料的共享（*****）（統計網站被訪問了多少次）

                    void setAttribute(String name, Object object)   存入資料
                    void removeAttribute(String name)                  刪除資料

                    Object getAttribute(String name)                  獲取資料

兩個servlet實現：

CountServlet.java

package cn.itcast.context;

import java.io.IOException;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * 統計網站的訪問次數
 * @author Administrator
 *
 */
public class CountServlet extends HttpServlet {

	/**
	 * 例項被建立，呼叫init方法初始化
	 * 在域物件中存入一個變數，賦值0
	 */
	public void init() throws ServletException {
		getServletContext().setAttribute("count", 0);
	}

	/**
	 * 每次訪問，都會執行該方法
	 * 拿出count值，然後自加，再存入域中
	 */
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		ServletContext context = getServletContext();
		Integer count = (Integer) context.getAttribute("count");
		count++;
		//存入域物件中
		context.setAttribute("count", count);
		
		//向頁面輸出
		response.setContentType("text/html; charset=UTF-8");
		response.getWriter().write("<h1> 歡迎再來哦！！！ </h1>");
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		doGet(request, response);
	}

}

showServlet.java

package cn.itcast.context;

import java.io.IOException;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * 顯示網站的訪問量
 * @author Administrator
 *
 */
public class ShowServlet extends HttpServlet {

	/**
	 * 獲取網站訪問次數
	 */
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		ServletContext context = getServletContext();
		Integer count = (Integer) context.getAttribute("count");
		
		//向頁面輸出
		response.setContentType("text/html; charset=UTF-8");
		response.getWriter().write("<h1>該網站一共被訪問了" + count + "次</h1>");
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		doGet(request, response);
	}

}

2.3讀取資原始檔（*****）

                    InputStream getResourceAsStream(String path)      通過檔案的地址獲取輸入流

                    String getRealPath(String path)          通過檔案的地址獲取檔案的絕對磁碟路徑

package cn.itcast.context;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ReadServlet extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		read5();
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		doGet(request, response);
	}
	
	
	public void read5() throws IOException{
		String path = getServletContext().getRealPath("/WEB-INF/classes/db.properties");
		System.out.println(path);
		
		//servletContext來讀取檔案
		InputStream in = new FileInputStream(path);
		//列印方式
		print(in);
	}
	
	public void read2() throws IOException{
		//servletContext來讀取檔案
		InputStream in = getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
		//列印方式
		print(in);
		
	}
	
	/**
	 * 傳統方式讀取資原始檔
	 * 交給伺服器處理，相對位置在tomcat/bin
	 * @throws IOException
	 */
	public void read1() throws IOException{
		//獲取輸入流
		InputStream in = new FileInputStream("/src/db.properties");
		Properties pro = new Properties();
		
		//載入
		pro.load(in);
		
		//獲取檔案中的內容
		String username = pro.getProperty("username");
		String password = pro.getProperty("password");
		String desc     = pro.getProperty("desc");
		
		System.out.println("使用者名稱：" + username);
		System.out.println("密碼："  + password);
		System.out.println("描述："  + desc);
	}
	
	public void print(InputStream in) throws IOException{
		
		Properties pro = new Properties();
		//載入
		pro.load(in);
		
		//獲取檔案中的內容
		String username = pro.getProperty("username");
		String password = pro.getProperty("password");
		String desc     = pro.getProperty("desc");
		
		System.out.println("使用者名稱：" + username);
		System.out.println("密碼："  + password);
		System.out.println("描述："  + desc);
	}

}