Java add text to a specific line in a file

Question

I would like to know if it's possible to add a line in a File with Java.

For example myFile :

1: line 1
2: line 2
3: line 3
4: line 4

I would like to add a line fox example in the third line so it would look like this

1: line 1
2: line 2
3: new line
4: line 3
5: line 4

I found out how to add text in an empty file or at the end of the file but i don't know how to do it in the middle of the text without erasing the line.

Is the another way than to cut the first file in 2 parts and then create a file add the first part the new line then the second part because that feels a bit extreme ?

Thank you

You may use stackoverflow.com/questions/289965/…

nikli
– nikli

2016-05-17 13:04:09 +00:00
Commented May 17, 2016 at 13:04 — nikli
– nikli, Commented May 17, 2016 at 13:04

M. Suurland · Accepted Answer · 2016-05-17 13:38:34Z

13

In Java 7+ you can use the Files and Path class as following:

List<String> lines = Files.readAllLines(path, StandardCharsets.UTF_8);
lines.add(position, extraLine);
Files.write(path, lines, StandardCharsets.UTF_8);

To give an example:

Path path = Paths.get("C:\\Users\\foo\\Downloads\\test.txt");
List<String> lines = Files.readAllLines(path, StandardCharsets.UTF_8);

int position = lines.size() / 2;
String extraLine = "This is an extraline";  

lines.add(position, extraLine);
Files.write(path, lines, StandardCharsets.UTF_8);

edited May 17, 2016 at 13:38

answered May 17, 2016 at 13:05

M. Suurland

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5 Comments

user3718160 Over a year ago

Hello I tried to use this but I get an IDE error "usage of api which is not available at the configured language level". Apparently Path & Files are documented as 1.6+ but I'm using Java version 1.7 so it should work wright ? I don't really get it

M. Suurland Over a year ago

Please check the following: stackoverflow.com/questions/17714584/…

user3718160 Over a year ago

Even with that I keep seeing an error in my IDE but the code run so I will just ignore it thanks a lot !

M. Suurland Over a year ago

Welcome :) I am not running InteliJ (running Eclipse myself), but i guess it is related to your IDE.

Chris F Over a year ago

How can I extend this so I can add a line BEFORE a line with a certain string, e.g., add new line before that line that has line 4 in it?

Daniel Gutierrez · Accepted Answer · 2016-05-17 13:09:24Z

1

You may read your file into an ArrayList, you can add elements in any position and manipulate all elements and its data, then you can write it again into file.

PD: you can not add a line directly to the file, you just can read and write/append data to it, you must manipulte de data in memory and then write it again.

let me know if this is useful for you

answered May 17, 2016 at 13:09

Daniel Gutierrez

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