Reading a plain text file in Java

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}

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)

The easiest way is to use the Scanner class in Java and the FileReader object. Simple example:

Scanner in = new Scanner(new FileReader("filename.txt"));

Scanner has several methods for reading in strings, numbers, etc... You can look for more information on this on the Java documentation page.

For example reading the whole content into a String:

StringBuilder sb = new StringBuilder();while(in.hasNext()) {    sb.append(in.next());}in.close();outString = sb.toString();

Also if you need a specific encoding you can use this instead of FileReader:

new InputStreamReader(new FileInputStream(fileUtf8), StandardCharsets.UTF_8)