Read a file and replace certain line with a new one - java-8

Question

I want to:
Read a file,
Find a line that starts with certain word
Replace that line with a new one
Is there an efficient way of doing this using Java 8 Stream please?

Answer 1

Can you try this sample program. I read a file and look for a pattern, if I find a pattern I replace that line with a new one.
In this class:
- In method getChangedString, I read each line (Sourcefile is the path to the file you read)
- using map I check each line
- If I find the matching line, I replace it
- or else I leave the existing line as it is
- And finally return it as a List
import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;
import java.util.stream.Collectors;
public class FileWrite {
private static String sourceFile = "c://temp//data.js";
private static String replaceString = "newOrders: [{pv: 7400},{pv: 1398},{pv: 1800},{pv: 3908},{pv: 4800},{pv: 3490},{pv: 4300}";
public static void main(String[] args) throws IOException {
Files.write(Paths.get(sourceFile), getChangedString());
}
/*
* Goal of this method is to read each file in the js file
* if it finds a line which starts with newOrders
* then it will replace that line with our value
* else
* returns the same line
*/
private static List<String> getChangedString() throws IOException {
return Files.lines(Paths.get(sourceFile)) //Get each line from source file
//in this .map for each line check if it starts with new orders. if it does then replace that with our String
.map(line -> {if(line.startsWith("newOrders:" )){
return replaceString;
} else {
return line;
}
} )
//peek to print values in console. This can be removed after testing
.peek(System.out::println)
//finally put everything in a collection and send it back
.collect(Collectors.toList());
}
}