[Servlet] writes the file to the Respond output stream for users to download, and the respond output stream

[Servlet] writes the file to the Respond output stream for users to download, and the respond output stream

This article distinguishes the content originally printed to the console by writing Java to the Respond output stream for users to download (click to open the link, directly print it to a text file txt and download it to the user.

In fact, [Struts2] Chinese File Download and download permission control "(click to open the link) does not use three frameworks, which are purely implemented using servlets, how to download the file resources on the Tomcat server.

For example, the javaeedirectory structure is shown in the figure chrysanthemum.jpg at the root of the servletdownloadtestproject on the Tomcat server.

However, if you enter http: // localhost: 8080/ServletDownloadTest/download. java to access the Servlet "download", a download prompt box appears, for example:

After downloading the image, you can open it instead of directly displaying the image tag on the webpage like the img tag.

The display here is very simple. First of all, because the comments of Servlet3.0 are used, there is nothing in web. xml,

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns="http://java.sun.com/xml/ns/javaee"xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"version="3.0"></web-app>

The key is the code in download. java. After obtaining the real path where the server stores the file, write the file to the buffer first, and then write the buffer to the respond output stream for users to download.

Import java. io. *; import java.net. *; import javax. servlet. *; import javax. servlet. http. *; import javax. servlet. annotation. *; @ WebServlet (name = "download", urlPatterns = {"/download"}) public class download extends HttpServlet {private static final long serialVersionUID = 1L; protected void service (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {String file Path = this. getServletContext (). getRealPath ("/"); // obtain the actual path String downloadFilename = ".jpg with no question in Chinese"; // The default file name downloadFilename = URLEncoder is displayed in the download box. encode (downloadFilename, "UTF-8"); // encode the default downloaded file name. The unencoded result is that the File name is garbled during client download. file = new File (filePath + File. separator + "Chrysanthemum.jpg"); if (file. exists () {// specify the size of the file to be downloaded response. setContentLength (int) file. length (); response. setHeader ("Content-Disposition", "attachment; filename =" + downloadFilename); // set the default file name response displayed in the download box. setContentType ("application/octet-stream "); // specify that the returned object of response is a file stream // read the file to response // here, you first need to read the file content to the buffer zone // then write the buffer content to response output stream for users to download FileInputStream fileInputStream = new FileInputStream (file ); bufferedInputStream bufferedInputStream = new BufferedInputStream (fileInputStream); byte [] B = new byte [bufferedInputStream. available ()]; bufferedInputStream. read (B); OutputStream outputStream = response. getOutputStream (); outputStream. write (B); // walk bufferedInputStream. close (); outputStream. flush (); outputStream. close ();}}}

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