Use java to modify file contents in place

Question

I need to modify specific contents of a file in-place.
I do not want to create a new file and rewrite the old. Also the files are small

Answer 1

Assuming you want to be able to manipulate the file content as text, and assuming that the file fits in memory (which you say is a valid assumption), then perhaps you might find the methods in Commons IO FileUtils useful:

http://commons.apache.org/io/apidocs/org/apache/commons/io/FileUtils.html

For example:

File f = new File("my-file.txt");
List lines = FileUtils.readLines(f, "UTF-8");
List outLines = modify(lines); // Do some line-by-line text processing
FileUtils.writeLines(f, "UTF-8", outLines);

So, you're reading the file content into memory, modifying it in-memory, and then over-writing the original file with the new content from memory. Does that meet your criteria for "in-place"?