javaWeb:ServletContext学习

• • 1.ServletContext对象之获取web项目信息
  • 2.利用：ServletContext:获取公共属性
  • 3.ServletContext:获取读取web项目下的文件：
  • 4.ServletContext：ServletContext对象之作为域对象存取数据：

在：服务器目录conf下的：web.xml文件里面：有

        text  //索引
        text/plain//文本类型
    

创建一个类：

 ServletContext servletContext=this.getServletContext();//创建ServletContext对象
        String mineType=servletContext.getMimeType("aa.txt");//aa.text,文本类型是txt ，servletContext.getMimeType();对象的：API,返回类型
                System.out.println(mineType);

package com.example.demo16;


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;
import java.util.Enumeration;

public class HelloSerrvlet3 extends HttpServlet {


    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //super.doGet(req, resp);
        resp.getWriter().println("helloWolrd!");
        ServletConfig config=this.getServletConfig();//创建对象ServletConfig
      //  String username=config.getInitParameter("username");//得到配置里面的值

       // String password=config.getInitParameter("password");//也得到了
    //    System.out.println(username+"  "+password);
        Enumeration names=config.getInitParameterNames();//获得所有参数值
        while (names.hasMoreElements()){

            String name=names.nextElement();
            String value=config.getInitParameter(name);
            System.out.println(name+" "+value);

        }

        String servletName=config.getServletName();//获类取名称
        System.out.println(servletName);


        ServletContext servletContext=this.getServletContext();
        String mineType=servletContext.getMimeType("aa.txt");//aa.text,文本类型是txt
                System.out.println(mineType);             //就会打印出类型


    }


    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.doPost(req, resp);
    }
}

配置：公共属性web.xml中

    username
    root


    
        password
        123

    

在 doGet(）{}，增加下面代码：

String username=servletContext.getInitParameter("username");
        String password=servletContext.getInitParameter("password");

        System.out.println(username+" "+password); //获得值


        Enumeration names=servletContext.getInitParameterNames();  



        while (names.hasMoreElements()) {  //遍历


            String name=names.nextElement();
             String value=config.getInitParameter(name);
             System.out.println(name+" "+value);

        }

效果：

xml文件配置：

    username
    root


    
        password
        123

    




    
        demo2
        com.example.demo16.HelloServlet2





        1


    



    demo2
    /hello




    
        demo3
        com.example.demo16.HelloSerrvlet3

        
            username
            root
        

        
            password
            abc
        

    


    
        demo3
        /helloo
    

创建类:HelloServlet4

WEB-INF/dp.properties:（IDEA中）

要放在：WEB-INF下面：建立dp.properties文件

那么：就会在：服务器目录：有WEB-INF/dp.properties.
就可以服务器被访问到

 InputStream is=this.getServletContext().getResourceAsStream("WEB-INF/dp.properties");

package com.example.demo16;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

public class HelloServlet4 extends HttpServlet {


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

resp.getWriter().println("helloworld");

text();

    }



    protected void text() throws IOException {

        Properties properties=new Properties();//创建文件对象
        InputStream is=this.getServletContext().getResourceAsStream("WEB-INF/dp.properties");//这里的路径，

          properties.load(is);
String driverClassName=properties.getProperty("driverClassName");
        String url=properties.getProperty("url");
      String  password=properties.getProperty("password");
        String usernane=properties.getProperty("username");

        System.out.println(driverClassName);
System.out.println(url);
System.out.println(password);
System.out.println(usernane);

    }



    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.doPost(req, resp);
    }
}

xml配置：

        demo4
        com.example.demo16.HelloServlet4

        1


    


    
        demo4
        /htrt

    

效果：

在：init(){}放：
this.getServletContext().setAttribute(“name”,“张三”);
在doget(){}放：

String name= (String) this.getServletContext().getAttribute(“name”);
System.out.println(name);
结果：打印出张三

另外：在其他的类也可以使用：
this.getServletContext().getAttribute(“name”);
System.out.println(name);//打印出数据

package com.example.demo16;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

public class HelloServlet4 extends HttpServlet {

    @Override
    public void init() throws ServletException {
        super.init();

        this.getServletContext().setAttribute("name","张三");
    }

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

resp.getWriter().println("helloworld");



        String name= (String) this.getServletContext().getAttribute("name");
        System.out.println(name);
//text();

    }



    protected void text() throws IOException {

        //Properties properties=new Properties();//创建文件对象
        //InputStream is=this.getServletContext().getResourceAsStream("WEB-INF/dp.properties");//这里的路径，

        //  properties.load(is);
//String driverClassName=properties.getProperty("driverClassName");
       // String url=properties.getProperty("url");
      //String  password=properties.getProperty("password");
      //  String usernane=properties.getProperty("username");

      //  System.out.println(driverClassName);
//System.out.println(url);
//System.out.println(password);
//System.out.println(usernane);



    }



    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.doPost(req, resp);
    }
}