ServletContext对象

ServletContext对象：

1. 概念：代表整个web应用，可以和程序的容器(服务器)来通信
2. 获取：
	1. 通过request对象获取
		request.getServletContext();
	2. 通过HttpServlet获取
		this.getServletContext();

*例子：

package cn.itcast.web.servletContext;

import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

@WebServlet("/servletContextDemo1")
public class ServletContextDemo1 extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        /*
        ServletContext对象获取：
            1.通过request对象获取
                req.getServletContext();
            2.通过HttpServlet获取
                this.getServletContext();
         */
        ServletContext s1 = req.getServletContext();
        ServletContext s2 = this.getServletContext();

        System.out.println(s1==s2);
    }

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

3. 功能：
	1. 获取MIME类型：
		* MIME类型:在互联网通信过程中定义的一种文件数据类型
			* 格式： 大类型/小类型   text/html		image/jpeg

		* 获取：String getMimeType(String file)  

*例子

package cn.itcast.web.servletContext;


import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

@WebServlet("/servletContextDemo2")
public class ServletContextDemo2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        /*
        获取MIME类型：
            MIME类型：在互联网通信过程中定义的一种文件数据类型
                格式：大类型/小类型 text/html image/jpeg
         */
        ServletContext servletContext = this.getServletContext();

        //定义文件名称
        String file = "a.jpg";
        //获取MIME类型
        String mimeType = servletContext.getMimeType(file);
        System.out.println(mimeType);
    }

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

	2. 域对象：共享数据
		1. setAttribute(String name,Object value)
		2. getAttribute(String name)
		3. removeAttribute(String name)

		* ServletContext对象范围：所有用户所有请求的数据

*例子：

package cn.itcast.web.servletContext;

import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

@WebServlet("/servletContextDemo4")
public class ServletContextDemo4 extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        //获取数据
        Object msg = context.getAttribute("msg");
        System.out.println(msg);
    }

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

package cn.itcast.web.servletContext;

import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

@WebServlet("/servletContextDemo3")
public class ServletContextDemo3 extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        /*
        域对象：共享数据
         */


        ServletContext context = this.getServletContext();
        //设置数据
        context.setAttribute("msg","hello");
    }

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

	3. 获取文件的真实(服务器)路径
		1. 方法：String getRealPath(String path)  
			 String b = context.getRealPath("/b.txt");//web目录下资源访问
	         System.out.println(b);
	
	        String c = context.getRealPath("/WEB-INF/c.txt");//WEB-INF目录下的资源访问
	        System.out.println(c);
	
	        String a = context.getRealPath("/WEB-INF/classes/a.txt");//src目录下的资源访问
	        System.out.println(a);

*例子：

package cn.itcast.web.servletContext;

import jakarta.servlet.ServletContext;
import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

@WebServlet("/servletContextDemo5")
public class ServletContextDemo5 extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        //获取服务器的路径
        String b = context.getRealPath("/b.txt");
        System.out.println(b);
        String a = context.getRealPath("/WEB-INF/classes/a.txt");
        System.out.println(a);

    }

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