GetPictureFile

package com.controller;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URLEncoder;
import java.sql.SQLException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.dao.IPictureTableDao;
import com.dao.impl.PictureTableMSSQLDao;
import com.model.PictureTable;

@WebServlet("/GetPictureFile")
public class GetPictureFile extends HttpServlet {
    private static final long serialVersionUID = 1L;

    public GetPictureFile() {
        super();
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // response.getWriter().append("Served at: ").append(request.getContextPath());

        String indexStr = "";
        int index = 0;
        indexStr = request.getParameter("id");

        // System.out.println("indexStr = " + indexStr);

        if (indexStr == null) {
            // 如果沒有 query string 就結束這段程式。
            System.out.println("無 query string ，抓取圖片id失敗。");
            RequestDispatcher requestDispatcher = request.getRequestDispatcher("viewAllPicture.jsp");
            requestDispatcher.forward(request, response);
            return;
        }

        try {
            index = Integer.parseInt(indexStr);
        } catch (NumberFormatException e) {
            e.printStackTrace();
            // 如果不是合法數字就結束這段程式。
            System.out.println("圖片id非合法數字。");
            RequestDispatcher requestDispatcher = request.getRequestDispatcher("viewAllPicture.jsp");
            requestDispatcher.forward(request, response);
            return;
        }

        IPictureTableDao pictureDao = new PictureTableMSSQLDao();
        PictureTable pictureTable = pictureDao.getPictureWithBlobById(index);

        if (pictureTable == null) {
            // 查無資料，結束程式。
            System.out.println("查無資料，結束程式。");
            RequestDispatcher requestDispatcher = request.getRequestDispatcher("viewAllPicture.jsp");
            requestDispatcher.forward(request, response);
            return;
        }

        String pictureName = pictureTable.getPictureName();
        InputStream inputStream = null;
        long fileLength = 0L;
        try {
            inputStream = pictureTable.getFile2().getBinaryStream();
            fileLength = pictureTable.getFile2().length();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        OutputStream outputStream = null;

        // String mimeType = this.getServletContext().getMimeType(pictureName);
        // System.out.println("mimeType = " + mimeType);

        // 原文網址：https://kknews.cc/code/n5xn4yq.html
        String userAgent = request.getHeader("User-agent");
        userAgent = userAgent.toLowerCase();
        System.out.println("userAgent");
        System.out.println(userAgent);

        boolean isInternetExplorer = false;
        if (userAgent.indexOf("trident") != -1 || userAgent.indexOf("wow64") != -1 || userAgent.indexOf("edge") != -1
                || userAgent.indexOf("edg") != -1) {
            System.out.println("Yes. It's Internet Explorer Browser. It's Microsoft Edge Browser");
            isInternetExplorer = true;
        } else {
            isInternetExplorer = false;
        }

        if (false == isInternetExplorer) {
            // Google, Firefox, Opera瀏覽器
            pictureName = new String(pictureName.getBytes(), "ISO8859-1");
        } else {
            // Internet Explorer, Microsoft Edge瀏覽器
            pictureName = URLEncoder.encode(pictureName, "UTF-8");
            pictureName = pictureName.replace("+", "%20");
        }

        // 清空response
        response.reset();
        // 設定response的Header
        /* FireFox瀏覽器 必須在 fileName前後加上 \" 才能避免瀏覽器擷取到空格就停止擷取檔案名稱。 */
        response.addHeader("Content-Disposition", "attachment;filename=\"" + pictureName + "\"");
        // 這行程式碼設定檔案的名稱，為了避免中文字變亂碼，必須做額外處理。

        response.addHeader("Content-Length", String.valueOf(fileLength));
        response.setContentType("application/octet-stream");

        outputStream = response.getOutputStream();
        byte[] byteBuffer = new byte[(int) fileLength];
        int length = 0;
        try {
            while ((length = inputStream.read(byteBuffer)) != -1) {
                outputStream.write(byteBuffer, 0, length);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (outputStream != null) {
                outputStream.close();
                outputStream = null;
            }
            if (inputStream != null) {
                inputStream.close();
                inputStream = null;
            }
        }

    }// end of doGet() method
}