​​概念：​​

​​功能​​

​​获取MIME类型​​

​​域对象：共享数据​​

​​获取文件的 真实（服务器）路径​​



概念：

  • 代表整个web应用，可以和程序的容器（服务器）来通信



功能


  • 获取MIME类型
  • 域对象：共享数据
  • 获取文件的 真实（服务器）路径



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，如text/html         image/jpeg
  • 基本的类型可以从tomcat的配置文件web.xml找

ServletContext介绍与文件真实路径的获取_ServletContext

ServletContext介绍与文件真实路径的获取_java_02




下面我们就写个例子来展示一下



ContextDemo1代码，获取jpg文件的MIME类型，在浏览器输出


package com.lingaolu.servletContext;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.io.IOException;

/**
 * @author 林高禄
 * @create 2020-07-13-8:37
 */
@WebServlet("/contextDemo1")
public class ContextDemo1 extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();
        String aa = "a.jpg";
        String mimeType = servletContext.getMimeType(aa);
        response.getWriter().write(mimeType);
    }

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


启动访问

ServletContext介绍与文件真实路径的获取_服务器_03



域对象：共享数据



ServletContext的域范围是整个web应用，我们演示一下，在ContextDemo2存入数据name，在ContextDemo3取出数据



ContextDemo2代码


package com.lingaolu.servletContext;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.io.IOException;

/**
 * @author 林高禄
 * @create 2020-07-13-8:37
 */
@WebServlet("/contextDemo2")
public class ContextDemo2 extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();
        servletContext.setAttribute("name","爱Java,爱老婆");
    }

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


ContextDemo3代码


package com.lingaolu.servletContext;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.io.IOException;

/**
 * @author 林高禄
 * @create 2020-07-13-8:37
 */
@WebServlet("/contextDemo3")
public class ContextDemo3 extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();
        Object name = servletContext.getAttribute("name");
        response.setContentType("text/html;charset=utf-8");
        response.getWriter().write(name.toString());
    }

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


启动浏览器先访问/contextDemo2

ServletContext介绍与文件真实路径的获取_ide_04



此时ServletContext已经有数据name了，再访问/contextDemo3

ServletContext介绍与文件真实路径的获取_服务器_05



获取文件的 真实（服务器）路径



因为项目是部署到外面的服务器上的，所以将来文件的路径是部署后的路径，而不是我们本地项目的文件路劲，所以要获取文件，就要获取文件的真实路径



我们新建3个文件


  • context1.text：放在web目录下
  • context2.text：放在WEB-INF目录下
  • context3.text：放在src目录下

ServletContext介绍与文件真实路径的获取_java_06



我们先看一下我们项目的真实路径大的根目录是什么，给个空字符串说明访问的是根目录，ContextDemo4代码


package com.lingaolu.servletContext;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.io.IOException;

/**
 * @author 林高禄
 * @create 2020-07-13-8:37
 */
@WebServlet("/contextDemo4")
public class ContextDemo4 extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext servletContext = this.getServletContext();
        String realPath = servletContext.getRealPath("");
        response.getWriter().write(realPath);
    }

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


运行访问

ServletContext介绍与文件真实路径的获取_服务器_07



复制到我们电脑上查找

ServletContext介绍与文件真实路径的获取_ide_08



看到context1.text了，也看到了WEB-INF，说明我们真实路径的根目录就是web目录，所以我们web目录下的文件可以轻松直接访问，WEB-INF下也能访问了，那么src目录下的呢

src目录下的东西，最终会被放到WEB-INF目录下的classes文件下

ServletContext介绍与文件真实路径的获取_ServletContext_09



知道了context3.text的真实路径后，也就能访问了，下面就举个例子演示



ContextDemo5代码


package com.lingaolu.servletContext;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.io.IOException;
import java.io.PrintWriter;

/**
 * @author 林高禄
 * @create 2020-07-13-8:37
 */
@WebServlet("/contextDemo5")
public class ContextDemo5 extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        ServletContext servletContext = this.getServletContext();
        String context1 = servletContext.getRealPath("/context1.text");
        writer.write("context1的真实路径为:"+context1+"<br>");
        String context2 = servletContext.getRealPath("/WEB-INF/context2.text");
        writer.write("context2的真实路径为:"+context2+"<br>");
        String context3 = servletContext.getRealPath("/WEB-INF/classes/context1.text");
        writer.write("context3的真实路径为:"+context3+"<br>");
    }

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


运行访问

ServletContext介绍与文件真实路径的获取_ide_10