Outputstream the file through http response

[Anandha Loganathan]

I have the requirement like this
1) I have to create a file which would contain data from DB
2) and outputstream this file to http response.

eg: if the request is "http://localhost/abcd/product.csv "
then the user should save the file from his browser.

I have never worked on IO object and I have little knowledge about FileWriter, OutputStreams. Not sure If I have to use Objectoutstream for this purpose ?.

I could manage Mime type, buffer and other properties.

I would really appreciate if some one could help me on this.

[Anandha Loganathan]

I found solution but Do you have an elegant way to do this code.

   	FileWriter sw= new FileWriter("products.csv");
	 		CSVWriter writer = new CSVWriter(sw, '\u0009');
	 		for(int i=0;i <l.size();i++){
				Object[] obj=(Object[])l.get(i);
				writer.writeNext(convertObjectToString(obj));
		  	}
	 	 
	 		sw.close();
	 		
	 		FileInputStream fis = new FileInputStream("products.csv");
			byte b[];
			int x = fis.available();
			b = new byte[x];
			System.out.println(" b size"+b.length);
			fis.read(b);
			
			// FIXME: this is ugly
			if (response != null)
				response.setContentType(mimeType);
			
			OutputStream os = response.getOutputStream();
	        os.write(b);
	        os.flush();	
 

>

[Greg Charles]

That looks about right to me. It a good idea to set the content length of the response as well. I've run into trouble with that before, but it was only when sending the response to a non-standard browser. The normal browsers seemed happy enough with the 0 content length.

If you expect the file to be large, you could read it a chunk at a time and write each chunk immediately to the output stream. That avoids having the whole file resident in a byte array. Actually, unless you need the file for other reasons, you could just let the CSVWriter() write it directly to the servlet output stream (well, through a OutputStreamWriter anyway). In that case, you probably won't know the size though, so you have to hope a 0 content length won't freak out your client.

[Anandha Loganathan]

I couldn't get you. How do we use OutputStreamWriter?.

If you could provide me the example code then I would appreciate that.

Thanks
Ananda

[Greg Charles]

Oh, I just meant you needed an OutputStreamWriter to fit your interface. Something like this:

    
		response.setContentType(mimeType);
		
		OutputStream os = response.getOutputStream();
 		CSVWriter writer = new CSVWriter(new OutputStreamWriter(os), '\u0009');
 		for(int i=0;i <l.size();i++){
			Object[] obj=(Object[])l.get(i);
			writer.writeNext(convertObjectToString(obj));
	  	}
 	 
 		writer.flush();

>

[Anandha Loganathan]

Wrote the code in a better way.

  	 		response.setContentType(mimeType);
 	 		OutputStream fout= response.getOutputStream();
 	        OutputStream bos = new BufferedOutputStream(fout); 
  			OutputStreamWriter       outputwriter       = new OutputStreamWriter(bos);
 	 		 
  			CSVWriter writer = new CSVWriter(outputwriter);
	 		 for(int i=1;i <l.size();i++){	 		 
  	 			Object[] obj=(Object[])l.get(i);
				if(obj!=null){
 					writer.writeNext(convertObjectToString(obj));
  				}				
 	 		} 	

	 		 
	 		outputwriter.flush(); 
	 		outputwriter.close();   

>

[Anandha Loganathan]

Greg thanks for your help.

[Greg Charles]

You're welcome. IIRC, you don't want to close the servlet output stream though. Your close() call will chain all the way through. If it doesn't cause you any problems though, I guess it's OK.