Java: reading strings from a random access file with buffered input

Question

I\'ve never had close experiences with Java IO API before and I\'m really frustrated now. I find it hard to believe how strange and complex it is and how hard it could be to

Answer 1

I think the confusion is caused by the UTF-8 encoding and the possibility of double byte characters.

UTF8 doesn't specify how many bytes are in a single character. I'm assuming from your post that you are using single byte characters. For example, 412 bytes would mean 411 characters. But if the string were using double byte characters, you would get the 206 character.

The original java.io package didn't deal well with this multi-byte confusion. So, they added more classes to deal specifically with strings. The package mixes two different types of file handlers (and they can be confusing until the nomenclature is sorted out). The stream classes provide for direct data I/O without any conversion. The reader classes convert files to strings with full support for multi-byte characters. That might help clarify part of the problem.

Since you state you are using UTF-8 characters, you want the reader classes. In this case, I suggest FileReader. The skip() method in FileReader allows you to pass by X characters and then start reading text. Alternatively, I prefer the overloaded read() method since it allows you to grab all the text at one time.

If you assume your "bytes" are individual characters, try something like this:

FileReader fr = new FileReader( new File("x.txt") );
char[] buffer = new char[ pos2 - pos ];
fr.read( buffer, pos, buffer.length );
...