IntelliJ“ inputstream.read的结果被忽略”-如何解决？

Question

I'm working on fixing some potential bugs in my application. I'm using Sonar to evaluate my code. My issue is this:

private Cipher readKey(InputStream re) throws Exception {
    byte[] encodedKey = new byte[decryptBuferSize];
    re.read(encodedKey); //Check the return value of the "read" call to see how many bytes were read. (the issue I get from Sonar)


    byte[] key = keyDcipher.doFinal(encodedKey);
    Cipher dcipher = ConverterUtils.getAesCipher();
    dcipher.init(Cipher.DECRYPT_MODE, new SecretKeySpec(key, "AES"));
    return dcipher;
}

Does this mean that the byte array was empty? Why is it being ignored? I've never worked with bytes so I was wondering what exactly this issue means and how I can address it. I appreciate your assistance!

Answer 1

Does this mean that the byte array was empty?

NO - this is no't an error

look at read(byte[]) method from definition of:

public abstract class InputStream extends Object implements Closeable {

     /**
     * Reads up to {@code byteCount} bytes from this stream and stores them in
     * the byte array {@code buffer} starting at {@code byteOffset}.
     * Returns the number of bytes actually read or -1 if the end of the stream
     * has been reached.
     *
     * @throws IndexOutOfBoundsException
     *   if {@code byteOffset < 0 || byteCount < 0 || byteOffset + byteCount > buffer.length}.
     * @throws IOException
     *             if the stream is closed or another IOException occurs.
     */
    public int read(byte[] buffer, int byteOffset, int byteCount) throws IOException {

       ....
    }

}

so what the IDE indicating? is that you omitting the result of read method - which is the number of bytes actually read or -1 if the end of the stream has been reached.

How to fix?

if u care how many bytes were read to byte buffer:

  // define variable to hold count of read bytes returned by method 
  int no_bytes_read = re.read(encodedKey);

why you should care ???

1. because when you read from stream you are passing as parameter often a buffer specially when you don't know the size of data being carried by stream or you want to read by portions (in this case you passing byte array of decryptedBuferSize size - > new byte[decryptBuferSize] ) .
2. at the beginning the byte buffer (byte array) is empty (filled with zeros)
3. method read() / read(byte[]) are reading one or many bytes from stream
4. to be aware how many bytes were "mapped/read from stream to buffer" you have to get the result of read(byte[]) method, this is useful because you don't need to check the content of buffer.
5. still at some point you need get the data from buffer / then you need to know the beginning and end offset of the data in buffer

for example:

 // on left define byte array   =  //  on right reserve new byte array of size 10 bytes 
  byte[] buffer =  new byte[10];
  // [00 00 00 00 00 00 00 00 00 00]  <- array in memory 
  int we_have_read = read(buffer);     // assume we have read 3 bytes 
  // [22 ff a2 00 00 00 00 00 00 00]  <- array after read 

 have we reached the end of steram or not ?  do we need still to read ? 

 we_have_read  ? what is the value of this variable ? 3 or -1 ? 

 if 3 ? do we need still read ? 
 or -1 ? what to do ? 

i encourage you to read more about io and nio api

http://tutorials.jenkov.com/java-nio/nio-vs-io.html

https://blogs.oracle.com/slc/entry/javanio_vs_javaio

http://www.skill-guru.com/blog/2010/11/14/java-nio-vs-java-io-which-one-to-use/