为什么InputStream.seek导致乱码内容？

Question

I have to read a resource partially, then later on (at a very different point in time), I need to skip the number of bytes I'd initially read. I need to glue the two parts I've read.

This is a very simplistic illustration of my code. I am using separate ByteArrayInputStream -s because, as mentioned above, the invocations will be totally unrelated to each other (almost certainly, not using the same InputStream ).

I am not quite sure what's going wrong here. Instead of getting a concatenated String with a value of This is a big fat super long text has no meaning, but is good for the test. , I am getting: This is a big fat super long text has no meaning, but is good for the test.aning, but is good fo .

public void testFoo()
{
    String s = "This is a big fat super long text has no meaning, but is good for the test.";

    ByteArrayInputStream bais1 = new ByteArrayInputStream(s.getBytes());
    ByteArrayInputStream bais2 = new ByteArrayInputStream(s.getBytes());

    ByteArrayOutputStream baos1 = new ByteArrayOutputStream();
    ByteArrayOutputStream baos2 = new ByteArrayOutputStream();

    int size = 32;
    byte[] bytes = new byte[size];

    int total = 0;
    int len;

    while ((len = bais1.read(bytes, 0, size)) != -1)
    {
        baos1.write(bytes);
        baos1.flush();

        total += len;
        if (total >= size)
        {
            // This is here just to illustrate that
            // we are reading a few bytes, and then
            // just terminating before the rest of
            // the stream has been read.
            break;
        }
    }

    bytes = new byte[size];
    bais1.close();

    System.out.println("Read " + total + " bytes.");

    // Here we are supposed to skip the number
    // of bytes that have already been read:
    bais2.skip(total);

    System.out.println("Skipped " + total + "/" + s.getBytes().length + " bytes.");

    while ((len = bais2.read(bytes, 0, size)) != -1)
    {
        baos2.write(bytes);
        baos2.flush();

        total += len;
    }

    System.out.println("Original:      " + s);
    System.out.println("Partial read1: " + new String(baos1.toByteArray()));
    System.out.println("Partial read2: " + new String(baos2.toByteArray()));

    System.out.println("Read " + total + " bytes.");
}

Could somebody please point out what's wrong and how to fix it? I don't quite understand why after skipping the number of bytes during the second read, the end of the read data gets messed up. Please, advise!

Answer 1

In your second read loop, you are ignoring the number of bytes read, so the bytes already in the buffer are being appended to the output stream.

Try changing it to this:

  System.out.println("Skipped " + total + "/" + s.getBytes().length + " bytes.");

  while ((len = bais2.read(bytes, 0, size)) != -1)
  {
    baos2.write(bytes, 0, len); // <- added write offset and length
    baos2.flush();

    total += len;
  }