Writing an entire list to a file in java

Question

I am working on a big project where I have more than 1 million lines of data. Data is divided into various files containing 20,000 lines each. Now the data from each file is read line by line and some variable x is concatenated to each line. I am storing these concatenated string to an array list. Then this array list is saved to output files line by line.

This is taking 3-4 minutes on each file. Is there anyway to write the entire ArrayList to a file in one go, so that it won't take that much time. Or is there any faster way to do this?

Here is some sample code:

    List<String> outputData = new ArrayList<String>(); 
//Output arraylist containing concatenated data

writeLines(File outputFile,outputData); //The data is written to file

What would be the fastest way to achieve this task?

Solution

Once you have the ArrayList ready you can use the writeLines method from FileUtils to write the entire ArrayList in one go.

Have a look at the documentation here and the various writeLines methods that are available.

Comments

[Ahmar Ali]

Hello thanks for answering but I used this solution also but it is way slower. Is there any faster way of file writing?

[Moritz Petersen]

How long are the lines? I just generated a file with 1.000.000 lines and it took less than 1 sec.