java.net.URL read stream to byte[]

Question

Hi folks :)

I`m trying to read an image from an URL (with the java package java.net.URL) to a byte[]. "Everything" works fine, except that the content isnt being enterely read from the stream (the image is corrupt, it doesnt contain all the image data)... The byte array is being persisted in a database (BLOB). I really dont know what the correct approach is, maybe you can give me a tip :)

This is my first approach (code formatted, removed unnecessary informations...):

URL u = new URL("http://localhost:8080/images/anImage.jpg");
int contentLength = u.openConnection().getContentLength();
Inputstream openStream = u.openStream();
byte[] binaryData = new byte[contentLength];
openStream.read(binaryData);
openStream.close();

My second approach was this one (as you'll see the contentlength is being fetched another way):

URL u = new URL(content);
openStream = u.openStream();
int contentLength = openStream.available();
byte[] binaryData = new byte[contentLength];
openStream.read(binaryData);
openStream.close();

Both of the code result in a corrupted image... I already read this post from stackoverflow

Answer 1

The content length is just a HTTP header. You cannot trust it. Just read everything you can from the stream.

Available is definitely wrong. It's just the number of bytes that can be read without blocking.

Another issue is your resource handling. Closing the stream has to happen in any case. try/catch/finally will do that.

Answer 2

There's no guarantee that the content length you're provided is actually correct. Try something akin to the following:

ByteArrayOutputStream bais = new ByteArrayOutputStream();
InputStream is = null;
try {
  is = url.openStream ();
  byte[] byteChunk = new byte[4096]; // Or whatever size you want to read in at a time.
  int n;

  while ( (n = is.read(byteChunk)) > 0 ) {
    bais.write(byteChunk, 0, n);
  }
}
catch (IOException e) {
  System.err.printf ("Failed while reading bytes from %s: %s", url.toExternalForm(), e.getMessage());
  e.printStackTrace ();
  // Perform any other exception handling that's appropriate.
}
finally {
  if (is != null) { is.close(); }
}

You'll then have the image data in bais, from which you can get a byte array by calling bais.toByteArray().

This code is untested (I just wrote it in the answer box), but it's a reasonably close approximation to what I think you're after.

Answer 3

Just extending Barnards's answer with commons-io. Separate answer because I can not format code in comments.

InputStream is = null;
try {
  is = url.openStream ();
  byte[] imageBytes = IOUtils.toByteArray(is);
}
catch (IOException e) {
  System.err.printf ("Failed while reading bytes from %s: %s", url.toExternalForm(), e.getMessage());
  e.printStackTrace ();
  // Perform any other exception handling that's appropriate.
}
finally {
  if (is != null) { is.close(); }
}

http://commons.apache.org/io/api-1.4/org/apache/commons/io/IOUtils.html#toByteArray(java.io.InputStream)