ServletContext域对象

* ServletContext域对象（接口）  

* 定义：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。

                  一个WEB应用对应一个ServletContext对象

                  一个WEB应用下有多个Servlet程序

                  一个web应用所有的servlet程序都共享同一个ServletContext对象

 

          demo1存入内容—》ServletContext—》demo2中取出来：ServletContext相当于一个媒介，demo1向其中存入数据，demo2可以冲其中取出数据。

* 获取全局初始化参数

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;

/**
 * 获取全局初始化参数
 * @author Administrator
 *
 */
public class ContextDemo1 extends HttpServlet {
    
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 先获取ServletContext对象
        ServletContext context = getServletContext();
        // 获取web.xml全局初始化参数
        String encoding = context.getInitParameter("encoding");
        System.out.println("编码："+encoding);
        //获取所有的参数名
        Enumeration<String> e = context.getInitParameterNames();
        while(e.hasMoreElements()){
            String name = e.nextElement();
            // 通过name获取值
            String value = context.getInitParameter(name);
            System.out.println(name+" : "+value);
        }
    }

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

}

 * 统计和显示网站的访问次数

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;

/**
 * 统计网站的访问次数
 * @author Administrator
 *
 */
public class CountServlet extends HttpServlet {
    
    /**
     * 实例被创建，调用init方法进行初始化
     *     在域对象存入一个变量，赋值为0
     */
    public void init() throws ServletException {
        // 获取ServletContext对象
        getServletContext().setAttribute("count", 0);
    }

    /**
     * 每一次访问，都会执行该方法。
     * 拿出count的变量，值自增，存入到域对象中
     */
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 先获取ServletContext对象
        ServletContext context = getServletContext();
        // 获取count的值，自增
        Integer count = (Integer) context.getAttribute("count");
        // 存入到域对象中
        context.setAttribute("count", ++count);
        
        // 向页面输出内容
        response.setContentType("text/html;charset=UTF-8");
        response.getWriter().write("<h3>大爷，欢迎再来哦！！</h3>");
    }

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

}

 

import java.io.IOException;

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

/**
 * 显示网站的访问次数
 * @author Administrator
 *
 */
public class ShowServlet extends HttpServlet {

    /**
     * 获取网站的访问次数，输出到客户端
     */
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        Integer count = (Integer) getServletContext().getAttribute("count");
        // 向页面输出
        response.setContentType("text/html;charset=UTF-8");
        response.getWriter().write("<h3>该网站一共被访问了"+count+"次</h3>");
    }

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

}

 * 读取资源文件

import java.io.FileInputStream;
import java.io.FileNotFoundException;
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;

/**
 * 读取资源文件
 * @author Administrator
 *
 */
public class ReadServlet extends HttpServlet {
    
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        read2();
    }
    
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }
    
    /**
     * 通过ServletContext对象获取文件的绝对磁盘路径
     * 获取src目录下文件
     * @throws IOException 
     */
    public void read5() throws IOException{
        // 获取对象
        String path = getServletContext().getRealPath("/WEB-INF/classes/db.properties");
        // System.out.println(path);
        // C:\apache-tomcat-6.0.14\webapps\day09\WEB-INF\classes\db.properties
        
        // 获取输入流
        InputStream in = new FileInputStream(path);
        print(in);
    }
    
    /**
     * 获取WebRoot目录目录下db.properties文件
     * @throws IOException
     */
    public void read4() throws IOException{
        // ServletContext读取文件
        InputStream in = getServletContext().getResourceAsStream("/db.properties");
        // 打印方式
        print(in);
    }
    
    /**
     * 获取包目录下db.properties文件
     * @throws IOException
     */
    public void read3() throws IOException{
        // ServletContext读取文件
        InputStream in = getServletContext().getResourceAsStream("/WEB-INF/classes/cn/itcast/context/db.properties");
        // 打印方式
        print(in);
    }
    
    /**
     * 获取src目录下db.properties文件
     * @throws IOException   编译后，src文件不见了，全都放在class文件里
     */
    public void read2() throws IOException{
        // ServletContext读取文件
        InputStream in = getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
        // 打印方式
        print(in);
    }
    
    /**
     * 传统方式读取资源文件
     *     交给服务器处理，相对的位置tomcat/bin
     * @throws IOException 
     */
    public void read1() throws IOException{
        // 获取输入流
        InputStream in = new FileInputStream("src/db.properties");
        print(in);
    }
    
    /**
     * 在控制台打印内容
     * @param in
     * @throws IOException
     */
    public void print(InputStream in) throws IOException{
        Properties pro = new Properties();
        // 加载
        pro.load(in);
        // 获取文件中的内容
        String username = pro.getProperty("username");
        String password = pro.getProperty("password");
        String desc = pro.getProperty("desc");
        
        System.out.println("用户名："+username);
        System.out.println("密码："+password);
        System.out.println("描述："+desc);
    }
    
}

 配置文件db.properties

username=root33
password=12333
desc=haha33