In this tutorial we’re going to show how to use Java Scanner to read data from different input sources – String, File/Path, and InputStream.

The basic use of java.util.Scanner is like this:

try (Scanner scanner = new Scanner(input)) {
   // process data
}

We use try with resources to close the scanner, which automatically closes input if it implements Closeable interface.

Scanner can be used to read input data from simple Strings:

try (Scanner scanner = new Scanner("1 2 3 5 8 13")) {
    int sum = 0;
    while (scanner.hasNextInt()) {
        sum += scanner.nextInt();
    }
    System.out.println("Sum of numbers: " + sum);
}

The above example generates:

Sum of numbers: 32

To read from java.io.File use new File(“filename”):

Path source = Paths.get("/proc/meminfo");
System.out.println("Reading from file: " + source);
try (Scanner scanner = new Scanner(source)) {
    scanner.useDelimiter("\n");
    while (scanner.hasNext()) {
        System.out.println(scanner.next());
    }
}

Cut output of the above code:

Reading from file: /proc/meminfo
MemTotal:        8064000 kB
MemFree:          266620 kB
MemAvailable:    3502160 kB
...

Notice the change of delimiter to comma (,):

byte[] data = "one,two,three".getBytes();
InputStream source = new ByteArrayInputStream(data);
try (Scanner scanner = new Scanner(source)) {
    scanner.useDelimiter(",");
    while (scanner.hasNext()) {
        System.out.println(scanner.next());
    }
}

The above code produces:

one
two
three

• Java IO Tutorial to learn more about Paths