Downloading Multiple Files Using Multipart Response

Example to download multiple files using “multipart/x-mixed-replace”.

PS: This code does not work with Internet Explorer.

import java.io.BufferedInputStream; 
import java.io.File; 
import java.io.FileInputStream; 
import java.io.FileNotFoundException; 
import java.io.IOException; 
import java.util.ArrayList; 
import java.util.List; 
import javax.servlet.ServletException; 
import javax.servlet.ServletOutputStream; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse;

/**
 * Downloading Multiple Files using "multipart/x-mixed-replace".
 *
 * @author JavaDigest
 */
public class DownloadMultipleFiles extends HttpServlet {

  private static final long serialVersionUID = 3305561818342965462L;

  public void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {

    // Set the response type and specify the boundary string
    response.setContentType("multipart/x-mixed-replace;boundary=END");

    // Set the content type based on the file type you need to download
    String contentType = "Content-type: text/rtf";

    // List of files to be downloaded
    List files = new ArrayList();
    files.add(new File("C:/first.txt"));
    files.add(new File("C:/second.txt"));
    files.add(new File("C:/third.txt"));

    ServletOutputStream out = response.getOutputStream();

    // Print the boundary string
    out.println();
    out.println("--END");

    for (File file : files) {

      // Get the file
      FileInputStream fis = null;
      try {
        fis = new FileInputStream(file);

      } catch (FileNotFoundException fnfe) {
        // If the file does not exists, continue with the next file
        System.out.println("Could not find file " + file.getAbsolutePath());
        continue;
      }

      BufferedInputStream fif = new BufferedInputStream(fis);

      // Print the content type
      out.println(contentType);
      out.println("Content-Disposition: attachment; filename=" + file.getName());
      out.println();

      System.out.println("Sending file " + file.getName());

      // Write the contents of the file
      int data = 0;
      while ((data = fif.read()) != -1) {
        out.write(data);
      }
      fif.close();

      // Print the boundary string
      out.println();
      out.println("--END");
      out.flush();
      System.out.println("Finished sending file " + file.getName());
    }

    // Print the ending boundary string
    out.println("--END--");
    out.flush();
    out.close();
  }

}

Yet another way to achieve this will be to zip all the files before downloading, and then download the zip file as a zip attachment.

Downloading Multiple Files As Zip