Reading a plain text file in Java

Question

It seems there are different ways to read and write data of files in Java.

I want to read ASCII data from a file. What are the possible ways and their differences?

Answer 1

ASCII is a TEXT file so you would use Readers for reading. Java also supports reading from a binary file using InputStreams. If the files being read are huge then you would want to use a BufferedReader on top of a FileReader to improve read performance.

Go through this article on how to use a Reader

I'd also recommend you download and read this wonderful (yet free) book called Thinking In Java

In Java 7:

new String(Files.readAllBytes(...)) 

(docs) or

Files.readAllLines(...) 

(docs)

In Java 8:

Files.lines(..).forEach(...) 

(docs)

Answer 2

My favorite way to read a small file is to use a BufferedReader and a StringBuilder. It is very simple and to the point (though not particularly effective, but good enough for most cases):

BufferedReader br = new BufferedReader(new FileReader("file.txt")); try {     StringBuilder sb = new StringBuilder();     String line = br.readLine();      while (line != null) {         sb.append(line);         sb.append(System.lineSeparator());         line = br.readLine();     }     String everything = sb.toString(); } finally {     br.close(); } 

Some has pointed out that after Java 7 you should use try-with-resources (i.e. auto close) features:

try(BufferedReader br = new BufferedReader(new FileReader("file.txt"))) {     StringBuilder sb = new StringBuilder();     String line = br.readLine();      while (line != null) {         sb.append(line);         sb.append(System.lineSeparator());         line = br.readLine();     }     String everything = sb.toString(); } 

When I read strings like this, I usually want to do some string handling per line anyways, so then I go for this implementation.

Though if I want to actually just read a file into a String, I always use Apache Commons IO with the class IOUtils.toString() method. You can have a look at the source here:

http://www.docjar.com/html/api/org/apache/commons/io/IOUtils.java.html

FileInputStream inputStream = new FileInputStream("foo.txt"); try {     String everything = IOUtils.toString(inputStream); } finally {     inputStream.close(); } 

And even simpler with Java 7:

try(FileInputStream inputStream = new FileInputStream("foo.txt")) {          String everything = IOUtils.toString(inputStream);     // do something with everything string }