Question

Trying to tail / parse some log files. Entries start with a date then can span many lines.

This works, but does not ever see new entries to file.

File inputFile = new File("C:/test.txt");
InputStream is = new FileInputStream(inputFile);
InputStream bis = new BufferedInputStream(is);
//bis.skip(inputFile.length());
Scanner src = new Scanner(bis);
src.useDelimiter("\n2010-05-01 ");

while (true) {
    while(src.hasNext()){
    System.out.println("[ " + src.next() + " ]");
    }
}

Doesn’t seem like Scanner’s next() or hasNext() detects new entries to file.

Any idea how else I can implement, basically, a tail -f with custom delimiter.

---

ok – using Kelly’s advise i’m checking & refreshing the scanner, this works. Thank you !!

if anyone has improvement suggestions plz do!

File inputFile = new File("C:/test.txt");
InputStream is = new FileInputStream(inputFile);
InputStream bis = new BufferedInputStream(is);
//bis.skip(inputFile.length());
Scanner src = new Scanner(bis);
src.useDelimiter("\n2010-05-01 ");

while (true) {
    while(src.hasNext()){
    System.out.println("[ " + src.next() + " ]");
    }

    Thread.sleep(50);
    if(bis.available() > 0){
    src = new Scanner(bis);
    src.useDelimiter("\n2010-05-01 ");
    }
}

Answer 1

I would guess that the Scanner is parsing bis which is buffered but the buffer is never getting refreshed. You might be relying on the BufferedInputStream or the Scanner to keep reading bytes from the stream but I think you have to do that yourself.

From the Javadocs:

A BufferedInputStream adds
functionality to another input
stream-namely, the ability to buffer
the input and to support the mark and
reset methods. When the
BufferedInputStream is created, an
internal buffer array is created. As
bytes from the stream are read or
skipped, the internal buffer is
refilled as necessary from the
contained input stream, many bytes at
a time. The mark operation remembers a
point in the input stream and the
reset operation causes all the bytes
read since the most recent mark
operation to be reread before new
bytes are taken from the contained
input stream.