Question

In java, how to read a fixed length from the inputstream and save as a file?
eg. I want to read 5M from inputStream, and save as downloadFile.txt or whatever.(BUFFERSIZE=1024)

FileOutputStream fos = new FileOutputStream(downloadFile);
byte buffer [] = new byte[BUFFERSIZE];
int temp = 0;
while ((temp = inputStream.read(buffer)) != -1)
{
    fos.write(buffer, 0, temp);
}

Answer 1

Two options:

1. Just keep reading and writing until you either reach the end of the input or you’ve copied enough:

   byte[] buffer = new byte[1024];
   int bytesLeft = 5 * 1024 * 1024; // Or whatever
   FileInputStream fis = new FileInputStream(input);
   try {
     FileOutputStream fos = new FileOutputStream(output);
     try {
       while (bytesLeft > 0) {
         int read = fis.read(buffer, 0, Math.min(bytesLeft, buffer.length);
         if (read == -1) {
           throw new EOFException("Unexpected end of data");
         }
         fos.write(buffer, 0, read);
         bytesLeft -= read;
       }
     } finally {
       fos.close(); // Or use Guava's Closeables.closeQuietly,
                    // or try-with-resources in Java 7
     }
   } finally {
     fis.close(); 
   }
   

2. Read all 5M into memory in one call, e.g. using DataInputStream.readFully, and then write it out in one go. Simpler, but obviously uses more memory.