how to download large files without memory issues in java

Question

When I am trying to download a large file which is of 260MB from server, I get this error: java.lang.OutOfMemoryError: Java heap space. I am sure my heap size is less than 252MB. Is there any way I can download large files without increasing heap size?

How I can download large files without getting this issue? My code is given below:

String path= "C:/temp.zip";   
response.addHeader("Content-Disposition", "attachment; filename=\"test.zip\""); 
byte[] buf = new byte[1024];   
try {   

             File file = new File(path);   
             long length = file.length();   
             BufferedInputStream in = new BufferedInputStream(new FileInputStream(file));   
             ServletOutputStream out = response.getOutputStream();   

             while ((in != null) && ((length = in.read(buf)) != -1)) {   
             out.write(buf, 0, (int) length);   
             }   
             in.close();   
             out.close();

Answer 1

There are 2 places where I can see you could potentially be building up memory usage:

1. In the buffer reading your input file.
2. In the buffer writing to your output stream (HTTPOutputStream?)

For #1 I would suggest reading directly from the file via FileInputStream without the BufferedInputStream. Try this first and see if it resolves your issue. ie:

FileInputStream in = new FileInputStream(file);   

instead of:

BufferedInputStream in = new BufferedInputStream(new FileInputStream(file));   

If #1 does not resolve the issue, you could try periodically flushing the output stream after so much data is written (decrease chunk size if necessary):

ie:

try
{
    FileInputStream fileInputStream  = new FileInputStream(file);
    byte[] buf=new byte[8192];
    int bytesread = 0, bytesBuffered = 0;
    while( (bytesread = fileInputStream.read( buf )) > -1 ) {
        out.write( buf, 0, bytesread );
        bytesBuffered += bytesread;
        if (bytesBuffered > 1024 * 1024) { //flush after 1MB
            bytesBuffered = 0;
            out.flush();
        }
    }
}
finally {
    if (out != null) {
        out.flush();
    }
}