Servlet : zipservlet

rberthou — Sat, 29 Sep 2007 09:48:08 +0000

This article aims at presenting how to create a servlet that sends a zip file to the user. We create here a html page with a form where you can enter an url. The servlet will get the content of this url (only the html page, not the images or other frames), create a zip file with it, and send you the file.

This example can be used as a basis to do various things.

Sending a file with a servlet

This involves two headers: Content-Type and Content-Disposition. The content type is set to “application/zip”. The other one is used to specify the filename used by the browser when it starts downloading the file.
```
res.setContentType("application/zip");
res.setHeader("Content-Disposition","inline; filename=output.zip;");
```
This header replace “res.setHeader(“Content-Disposition”,”attachment; filename=output.zip;”);” (not work with IE5)

In this example, we create a zip file. We’ll discuss later on how to create such files. As soon as we get a byte array with the zip file, we are ready to send it.
We simply call out.println(zip) to send the file.

li>Creating a zip file Have you ever noticed the java.util.zip package ?

Basically, a zip file is created by adding ZipEntries to a ZipOutputStream.
Once we have create a ZipEntry with a file name, we are ready to write an array of byte to the ZipOutputStream. Then we close the entry, finish the work with a call to finish(). We finally get a String containing the zipped file.

zout.putNextEntry(new ZipEntry("file.html"));
zout.write(b,0,size);
zout.closeEntry();
zout.finish();
String zip=bout.toString();

package javaside.servlet.sample ;
 
/**
* zipservlet.java
*
*  Main class for sample servlet
*
*  @author : R. BERTHOU
*  URL    : http://www.berthou.com/
* -----------------------------------------------------------
* Ver  * Author     *  DATE    * Description
* ....................DD/MM/YY...............................
* 1.00 * R.BERTHOU  * 12/01/01 *
**********************************************************/
 
import java.io.*;
 
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.zip.*;
import java.net.*;
import java.util.*;
 
public class zipservlet extends HttpServlet {
 
     public void doGet (HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException
     {
          byte b[]=new byte[300000];
 
          URL url;
          String temp;
 
          ByteArrayOutputStream bout=new ByteArrayOutputStream();
          ZipOutputStream zout=new ZipOutputStream(bout);
          ServletOutputStream out = res.getOutputStream();
          ServletContext servletContext = getServletContext();
 
          if ((temp=req.getParameter("url"))!=null)
          {
               try {
                    url=new URL(temp);
                    URLConnection uc = url.openConnection();
 
                    DataInputStream input = new DataInputStream(uc.getInputStream());
 
                    int numRead=0;
                    int size=0;
 
                    while (numRead != -1) {
                         numRead = input.read(b,size,20000);
                         size+=numRead;
                    }
 
                    zout.putNextEntry(new ZipEntry("file.html"));
                    zout.write(b,0,size);
                    zout.closeEntry();
                    zout.finish();
                    String zip=bout.toString();
 
                    res.setContentType("application/zip");
                    res.setHeader("Content-Disposition","inline; filename=output.zip;");
 
                    out.println(zip);
                    out.flush();
 
               }
               catch (Exception e)
               {
                    res.setContentType("text/html");
                    out.println("");
                    out.println("");
                    out.println("An error has occured while processing "+temp+"");
                    out.println("Here is the exception: "+e+"");
                    e.printStackTrace(new PrintWriter(out));
                    out.println("");
                    out.println("");
               }
          }
     }
}

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Servlet : zipservlet