Write a binary downloaded file to disk in Java

27,224

Solution 1

Don't use a FileWriter - that's trying to convert the data into text.

Just use FileOutputStream.

byte[] buffer = new byte[8 * 1024];

InputStream input = urlConnect.getInputStream();
try {
  OutputStream output = new FileOutputStream(filename);
  try {
    int bytesRead;
    while ((bytesRead = input.read(buffer)) != -1) {
      output.write(buffer, 0, bytesRead);
    }
  } finally {
    output.close();
  }
} finally {
  input.close();
}

Solution 2

I know this question is already answered, but a simpler approach is to use Apache Commons IO's IOUtils.copy() method, which can fully copy an InputStream to an OutputStream.

Solution 3

DataInputStream is meant for reading Java primitives, not for generic data.

It's also redundant, as urlConnect.getInputStream(); already returns an InputStream, and all InputStreams support read().

is = urlConnect.getInputStream();

P.S. This is assuming is and bis are the same variable. Otherwise, you're reading the wrong stream in the loop.

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Updated on October 03, 2020

Comments

  • radius
    radius about 3 years

    I have a software that allow to write add-on in javascript files (.js) that allow to use Java function (I don't know if this is common, I never saw java call in javascript file before)

    I need to download a binary file from a webserver and write it to the hard drive. I tried the following code:

    baseencoder = new org.apache.commons.codec.binary.Base64();
    url = new java.net.URL("https://server/file.tgz");
    
    urlConnect = url.openConnection();
    urlConnect.setDoInput(true);
    urlConnect.setDoOutput(true);
    urlConnect.setRequestProperty("authorization","Basic "+ java.lang.String(baseencoder.encodeBase64(java.lang.String( username + ":" + password ).getBytes())));
    urlConnect.setRequestProperty("content-type","application/x-www-form-urlencoded");
    
    is = new java.io.DataInputStream(urlConnect.getInputStream());
    fstream = new FileWriter("C:\\tmp\\test.tgz");
    out = new BufferedWriter(fstream);
    while((data = is.read()) != -1){
        out.write(data);
    }
    
    out.close();
    is.close();
    

    The resulting file is no longer a valid gzip archive. I'm sorry if I did a huge error but I'm not a programmer and don't know Java too much.

  • Matt Ball
    Matt Ball about 14 years
    Also, you'll want to use the correct test condition in your while loop: while((data = is.read()) != null){ ... }.
  • radius
    radius about 14 years
    Thanks using a FileOutputStream works (i still use only a simple read() because it seems that it's not possible to use a byte buffer in javascript as it's not an object.
  • Gewure
    Gewure over 6 years
    Nice Information! Interesting to learn that despite what the naming suggest DataInputStream isn't for generic data..!