#Adam.Blog#

While working on ColdFusion applications with Railo on Tomcat I have been piecing together tools necessary to get these applications to do everything I need them to do. So I’ve bolted on Hibernate, a URL rewriter, and so on. Now I found myself needing an SMTP server of some type so that emails generated by the application don’t create a ColdFusion error. I then thought to myself, “Wouldn’t it be fun to write a small SMTP server?” So I did.

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I was approached tonight with a question on how one could download a file from a specific URL in Java. I had never done this in Java before, but I have done this very same task in C#, so I figured it couldn’t be too different of a solution. After a few minutes of digging here is what you need.

First, using the java.net package you will need the URL class. This class allows you to open a socket connection to a specified URL. This class also has the handy ability to open up a stream to the newly opened connection, allowing you to use the many Java stream and reader classes.

From here we probably want to actually save the file that we have a connection to and put it somewhere on our filesystem. To do this we will use a FileOutputStream class in the java.io package.

The concept is to read a specified number of bytes from the input steam into a buffer, write those out to our file output stream, and repeat until there are no more bytes to read. Below is a full code sample that connects to the Mura CMS website and download the newest version of their awesome software, then save it to a ZIP file on your C: drive (yes, Windows). Cheers, and happy coding!

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package com.adampresley.examples;
 
import java.net.*;
import java.io.*;
 
public class DownloadFile 
{
  public static void main(String[] args) 
  {
     try 
     {
        /*
         * Get a connection to the URL and start up
         * a buffered reader.
         */
        long startTime = System.currentTimeMillis();
 
        System.out.println("Connecting to Mura site...\n");
 
        URL url = new URL("http://www.getmura.com/currentversion/");
        url.openConnection();
        InputStream reader = url.openStream();
 
        /*
         * Setup a buffered file writer to write
         * out what we read from the website.
         */
        FileOutputStream writer = new FileOutputStream("C:/mura-newest.zip");
        byte[] buffer = new byte[153600];
        int totalBytesRead = 0;
        int bytesRead = 0;
 
        System.out.println("Reading ZIP file 150KB blocks at a time.\n");
 
        while ((bytesRead = reader.read(buffer)) > 0)
        {  
           writer.write(buffer, 0, bytesRead);
           buffer = new byte[153600];
           totalBytesRead += bytesRead;
        }
 
        long endTime = System.currentTimeMillis();
 
        System.out.println("Done. " + (new Integer(totalBytesRead).toString()) + " bytes read (" + (new Long(endTime - startTime).toString()) + " millseconds).\n");
        writer.close();
        reader.close();
     } 
     catch (MalformedURLException e) 
     {
        e.printStackTrace();
     }
     catch (IOException e)
     {
        e.printStackTrace();
     }
 
  }
 
}