What is the best way to iterate over the lines of a Java String?

Question

Currently I\'m using something like :

String[]lines = textContent.split(System.getProperty(\"line.separator\"));
for(String tmpLine : lines){
   //do somethi         


        

Answer 1

Scanner

What about the java.util.Scanner class added in Java 1.5?

In summary:

A simple text scanner which can parse primitive types and strings using regular expressions.

A Scanner breaks its input into tokens using a delimiter pattern, which by default matches whitespace. The resulting tokens may then be converted into values of different types using the various next methods.

and of note for your scenario:

The scanner can also use delimiters other than whitespace. This example reads several items in from a string:

     String input = "1 fish 2 fish red fish blue fish";
     Scanner s = new Scanner(input).useDelimiter("\\s*fish\\s*");
     System.out.println(s.nextInt());
     System.out.println(s.nextInt());
     System.out.println(s.next());
     System.out.println(s.next());
     s.close();

Answer 2

use BufferedReader with StringReader argument. BufferedReader has a method readLine() so you can read your string line by line.

    StringReader reader = new StringReader(myBigTextString);
    BufferedReader br = new BufferedReader(reader);
    String line;
    while((line=br.readLine())!=null)
    {
        //do what you want
    }

Answer 3

I believe you have a better API available starting with Java-11 where you can do the same using the String.lines() API which returns the stream of strings extracted from this string partitioned by line terminators.

public Stream<String> lines()

Usage of the same could be:-

Stream<String> linesFromString = textContent.lines();
linesFromString.forEach(l -> {  //do sth });

Important API Note :-

@implNote This method provides better performance than
          split("\R") by supplying elements lazily and
          by faster search of new line terminators.

Answer 4

Guava's Splitter works well. Especially as you can remove blank lines

Splitter splitter = Splitter.on(System.getProperty("line.separator"))
                            .trimResults()
                            .omitEmptyStrings();
for (String line : splitter.split(input)){
   // do work here
}

Answer 5

If you are using Java 1.8 (or Android) then try this:

new BufferedReader(new StringReader(str)).lines().forEachOrdered((line) -> {
    // process each line as you like
});

Docs state

The Stream is lazily populated, i.e., read only occurs during the terminal stream operation.

Which means this runs quicker than other solutions that first generate a massive array of Strings before iteration can begin.

If you are using Java 11 or later then the answer @Naman gave recommending String#lines() method is even cleaner and fast as well, see https://stackoverflow.com/a/50631579/215266

Answer 6

You could use String.indexOf()/String.substring()

String separator = System.getProperty("line.separator");
int index = textContent.indexOf(separator);

while (index > 0)
{
  int nextIndex = textContent.indexOf(separator, index + separator.length());
  String line = textContent.substring(index + separator.length(), nextIndex);

  // do something with line.
}