How does InputStream.read(byte[]) work?

Question

I'm trying to unzip a zip folder, I have problem understand how the ZipInputStream.read(byte[]) work. This code work just fine but I don't know if my file is bigger than the buffer I set how I'll operate.

byte[] buffer = new byte[1024];
zipIs = new ZipInputStream(new FileInputStream(FILE_PATH));
while ((entry = zipIs.getNextEntry()) != null) {

        String entryName = File.separator + entry.getName();

        // Call file input stream
        FileOutputStream fos = new FileOutputStream(entryName);

        int len;
        // Write current entry
        while ((len = zipIs.read(buffer)) > 0) {
            fos.write(buffer, 0, len);
        }
        fos.close();
      }

I did read the doc but I find it confusing, please help.

Stephen C · Accepted Answer · 2016-10-20T04:31:59.467

I have problem understand how the ZipInputStream.read(byte[]) work.

It is described in the javadocs for InputStream.read(bytes[]):

This code work just fine but i don't know if my file is bigger than the buffer i set how i'll operate.

That is what the loop is for.

    while ((len = zipIs.read(buffer)) > 0) {
        fos.write(buffer, 0, len);
    }

It reads one buffer at a time, setting len to the number of bytes read, until the read call returns zero (or less). Each buffer-full is written using len to say how many bytes to write, and then it repeats ...

The while ((a = call()) > 0) { syntax is simply exploiting the fact that an assignment (e.g. (a = call())) is an expression whose value that is the value that was assigned to the variable.

Reading streams is one situation where this idiom is commonly used. It is worth remembering it.

How does InputStream.read(byte[]) work?

1 Answers1