problem in downloading file from a URL.

[lalit.wientech]

Hi All,

I have a file on my local server tomcat.

I am trying to save this file to different location in my computer using a servlet . Servlet reads the file from the URL and writes to some location.
Here is the code.

      HttpURLConnection connection = null;
	   
	    //OutputStreamWriter wr = null;
        BufferedReader rd  = null;
        StringBuilder sb = null;
        String line = null;
      
        URL serverAddress = null;
      
        try {
        	
        	
            serverAddress = new URL("http://localhost:8080/data/video.flv");
            //set up out communications stuff
            connection = null;
          
            //Set up the initial connection
            connection = (HttpURLConnection)serverAddress.openConnection();
            connection.setRequestMethod("GET");
            connection.setDoOutput(true);
            connection.setReadTimeout(10000);
                      
            connection.connect();
                  
          
            rd  = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            sb = new StringBuilder();
            
            Writer output = new BufferedWriter(new FileWriter("/home/lalit/file.flv"));
            
            System.out.println(connection.getContentLength());    
            int length = connection.getContentLength();        	
            
           int contentLength = connection.getContentLength();   
           char buffer[] = new char[contentLength];  
           output.write(buffer, 0, contentLength); 	
        	       
            
            
            output.close();
                      
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (ProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        finally
        {
       
            rd = null;           
            connection = null;
        }

This successfully saves file at specified location but i am not able to open this file. I tried different file formats flv, 3GP, doc etc.


Thanks

[iluxa]

don't use Writers and Readers: they're for characters. Use InputStream and OutputStream, and their read (byte[] bytes) kind of methods, and you should be fine.

When you use Readers, they convert the in-coming bytes into characters according to some character encoding, and then convert the characters back to bytes when writing to the disk... and messing up your bytes along the way.

[Eranga]

Simple what iluxa says is in the way you download the file, the format is changed. Not it the correct format to open it and so on.

[lalit.wientech]

Thanks iluxa & eranga
Now it's working file
Here is my updated code.

{
		
	    HttpURLConnection connection = null;
	   
	   
        InputStream isR = null;
     
        URL serverAddress = null;
      
        try {
        	
        	
            serverAddress = new URL("http://localhost:8080/data/file.doc");
            //set up out communications stuff
            connection = null;
          
            //Set up the initial connection
            connection = (HttpURLConnection)serverAddress.openConnection();
            connection.setRequestMethod("GET");
            connection.setDoOutput(true);
            connection.setReadTimeout(10000);
                      
            connection.connect();
      
           // rd  = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            isR = connection.getInputStream();
          
            File file = new File("/home/lalit/file.doc");
            FileOutputStream foS =  new FileOutputStream(file);
            
       
            System.out.println(connection.getContentLength());
        	
      
        	long contentLength = connection.getContentLength();  
        	
        	int read = 1024;
        
        	byte buffer[] = new byte[read];  
       
        	int readBytes = 0;
        	while ((isR != null) && ((readBytes = isR.read(buffer)) != -1)) {
				foS.write(buffer, 0, readBytes);
			}
        	
        	
        	
            isR.close();
            foS.close();
                      
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (ProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        finally
        {
            //close the connection, set all objects to null
            connection.disconnect();
           connection = null;
        }
        
     
	}

[Eranga]

Please use code tags next time.

[Eranga]

Are you downloading a text file (doc file) as a flv?

[lalit.wientech]

hi eranga
i will keep in mind for code.
No i am not trying to convert doc to flv.
I was just trying to test this for different file formats. I have modified the mistake in post.

Thanks
Lalit

[Eranga]

That's much better lalit. Just for interest, if you change of that byte array from 1024 to some other value what would happen?

[lalit.wientech]

1024 means reads 1024 bytes from InputStrem if you will change this to x . Then it will try to read x bytes from InputStream.

[Eranga]

Yeah that's true. So why can't you change it. I mean what's the advantage/dis-advantage doing that.

[lalit.wientech]

hi eranga,

nice question.

We can change this value but it should not exceed the range of Integer.

I think that

byte buffer[] = new byte[1024];
with this value OS tries to load 1024 bytes in buffer.
If you have so smaller size say 100 then it will take more time in reading and writing.
It is important that you should increase this value depending upon your availiable memory, capacity of butter etc.

Please correct if i am wrong.

Thanks

[Eranga]

It is important that you should increase this value depending upon your availiable memory, capacity of butter etc.

Exactly, that's what I want to point to you. We have to thing about lots of things with the programming limitations, such as primitive types range and so on.