If this doesn't seem like a question for a Clojure group, I'll preface this by saying it is motivated by writing Clojure examples for a "Clojure cookbook" [1]. So far the examples are intended to work like the Perl examples from the 1st edition of the Perl Cookbook [2], but it may grow beyond that some day (e.g. its own text, examples specific to Clojure constructs that have no direct analog in Perl). In particular, there are examples there for doing random access on files in Chapter 8, and I was wondering whether I'm on the right track.
I know about the class RandomAccessFile [3], which provides byte-oriented I/O on a file with the ability to tell your current byte position, or seek to a specified byte position. I know that some of the subclasses of Reader have mark and reset methods, but those appear to have implementation-specific limitations on how far back you can go, and only let you mark one position. I'm interested in something that lets you jump anywhere. Is the only way with built-in Java classes as follows? Use a RandomAccessFile for opening and manipulating the file. When you want to read a character or string, read enough bytes into a byte array and use the String constructor with signature String(byte[] bytes, int offset, int length, String charsetName) to convert it to characters, or the CharsetDecoder class if you want more control over the details. When you want to write a string, use String's getBytes(String charsetName) method to convert it to a byte array and then write that byte array to the file. Are there other open source Java or Clojure libraries that can do this? If you know you are working with a fixed width character encoding like ASCII or ISO-8859, this seems relatively straightforward. I realize that with variable-length multi-byte character encodings like UTF-8, it would be a bad idea to seek to a random byte position and start trying to decode a UTF-8 character starting at that byte position. I'm thinking of cases where you have an index of byte positions of interest you want to jump to in the future that are known to be the first byte of a character in the appropriate encoding. I also realize that one must be very cautious in writing to the middle of such a file, since byte lengths of strings are variable. In general, restricting writing only to appending, or forgetting this idea altogether and using a database, are preferable in most cases. Thanks, Andy [1] https://github.com/jafingerhut/pleac-clojure forked from https://github.com/mbacarella/pleac-clojure It is easier to understand what the examples are intended to do if you read along with the text of the 1st ed Perl Cookbook. [2] The 2003 2nd edition is here: http://www.amazon.com/Perl-Cookbook-Second-Tom-Christiansen/dp/0596003137/ref=sr_1_1?ie=UTF8&qid=1325800290&sr=8-1 It has some section numbers and examples different from 1st ed, which you can see on line here: http://docstore.mik.ua/orelly/perl/cookbook/ [3] http://docs.oracle.com/javase/6/docs/api/java/io/RandomAccessFile.html -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
