ServletContext介绍与文件真实路径的获取

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

 

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

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

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

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

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

复制到我们电脑上查找

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

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