CODEWITHSUNDEEP
javafileoverwrite
Shawn Shroyer
Shawn Shroyer

Reputation: 923

How to edit a specific attribute in file?

So say you have a file that is written in XML or soe other coding language of that sort. Is it possible to just rewrite one line rather than getting the entire file into a string, then changing then line, then having to rewrite the whole string back to the file?

Upvotes: 0

Views: 50

Answers (2)

jbx
jbx

Reputation: 22168

If the line you want to replace is larger than the new line that you want to replace it with, then it is possible as long as it is acceptable to have some kind of padding (for example white-space characters ' ') which will not effect your application.

If on the other hand the new content are larger than the content to be replaced you will need to shift all the data downwards, so you need to rewrite the file, or at least from the replaced line onwards.

Since you mention XML, it might be you are approaching your problem in the wrong way. Could it be that what you need is to replace a specific XML node? In which case you might consider using DOM to read the XML into a hierarchy of nodes and adding/updating/removing in there before writing the XML tree back to the file.

Upvotes: 1

Jon Skeet
Jon Skeet

Reputation: 1502506

In general, no. File systems don't usually support the idea of inserting or modifying data in the middle of a file.

If your data file is in a fixed-size record format then you can edit a record without overwriting the rest of the file. For something like XML, you could in theory overwrite one value with a shorter one by inserting semantically-irrelevant whitespace, but you wouldn't be able to write a larger value.

In most cases it's simpler to just rewrite the whole file - either by reading and writing in a streaming fashion if you can (and if the file is too large to read into memory in one go) or just by loading the whole file into some in-memory data structure (e.g. XDocument), making the changes, and then saving the file again. (You may want to consider saving to a different file then moving the files around to avoid losing data if the save operation fails for some reason.)

If all of this ends up being too expensive, you should consider using multiple files (so each one is smaller) or a database.

Upvotes: 2

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