How can I read a large text file line by line using Java?

A common pattern is to use

try (BufferedReader br = new BufferedReader(new FileReader(file))) {    String line;    while ((line = br.readLine()) != null) {       // process the line.    }}

You can read the data faster if you assume there is no character encoding. e.g. ASCII-7 but it won't make much difference. It is highly likely that what you do with the data will take much longer.

EDIT: A less common pattern to use which avoids the scope of line leaking.

try(BufferedReader br = new BufferedReader(new FileReader(file))) {    for(String line; (line = br.readLine()) != null; ) {        // process the line.    }    // line is not visible here.}

UPDATE: In Java 8 you can do

try (Stream<String> stream = Files.lines(Paths.get(fileName))) {        stream.forEach(System.out::println);}

NOTE: You have to place the Stream in a try-with-resource block to ensure the #close method is called on it, otherwise the underlying file handle is never closed until GC does it much later.

Look at this blog:

• Java Read File Line by Line - Java Tutorial

The buffer size may be specified, or the default size may be used. The default is large enough for most purposes.

// Open the fileFileInputStream fstream = new FileInputStream("textfile.txt");BufferedReader br = new BufferedReader(new InputStreamReader(fstream));String strLine;//Read File Line By Linewhile ((strLine = br.readLine()) != null)   {  // Print the content on the console  System.out.println (strLine);}//Close the input streamfstream.close();

Once Java 8 is out (March 2014) you'll be able to use streams:

try (Stream<String> lines = Files.lines(Paths.get(filename), Charset.defaultCharset())) {  lines.forEachOrdered(line -> process(line));}

Printing all the lines in the file:

try (Stream<String> lines = Files.lines(file, Charset.defaultCharset())) {  lines.forEachOrdered(System.out::println);}