ServletContext_功能_获取文件服务器路径和文件下载_代码实现

ServletContext对象范围：所有用户所有请求的数据

　　获取文件的真实服务器路径

方法：String getRealpath(String path)

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

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext servletContext1 = this.getServletContext();
        String realPath = servletContext1.getRealPath("/b.txt");
        System.out.println(realPath);

        String realPath1 = servletContext1.getRealPath("/WEB-INF");
        System.out.println(realPath1);

        String a = servletContext1.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);
    }


}

文件下载_代码实现

案例：

　　文件下载显示超链接

　　点击超链接后弹出下载提示框

　　文件图片文件下载

分析：

　超链接指向的资源如果能够被浏览器解析，则浏览器中展示，如果不能解析，则弹出下载提示框。不满足需求。

　　任何资源都必须弹出下载提示框

　　使用响应设置资源的打开方式

步骤

　　定义页面，编辑超链接href属性，指向Servlet，传递资源名称filename

　　定义Servlet

　　　　获取文件名称

　　　　使用字节输出流加载文件进内存

　　　　制定Response的响应：Content-dispostion:attacgment;filename=xxx

　　　　将数据写出到Response输出流

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

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

        String filename = req.getParameter("filename");

        ServletContext servletContext = this.getServletContext();
        String realPath = servletContext.getRealPath("/ass/" + filename);
        FileInputStream fileInputStream = new FileInputStream(realPath);


        String mimeType = servletContext.getMimeType(filename);
        resp.setHeader("content-type",mimeType);
        resp.setHeader("content-disposition","attachment;filename="+filename);


        ServletOutputStream outputStream = resp.getOutputStream();
        byte[] bytes = new byte[1024];

        int len = 0;
        while ((len = fileInputStream.read(bytes))!= -1){
            outputStream.write(bytes,0,len);
        }

        fileInputStream.close();
        outputStream.close();

    }

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

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <a href="/ass/banner_2.jpg">图片</a>
    <a href="/ass/bna.mp4">视频</a>

    <a href="/downloadloadServlet?filename=banner_2.jpg">图片1</a>

    <a href="/downloadloadServlet?filename=bna.mp4">视频1</a>
</body>
</html>

posted on 2022-08-11 10:55 淤泥不染阅读(50) 评论(0) 收藏举报