Methods to access the character-based console device, if any, associated
with the current Java virtual machine.
Methods to access the character-based console device, if any, associated
with the current Java virtual machine.
Whether a virtual machine has a console is dependent upon the
underlying platform and also upon the manner in which the virtual
machine is invoked. If the virtual machine is started from an
interactive command line without redirecting the standard input and
output streams then its console will exist and will typically be
connected to the keyboard and display from which the virtual machine
was launched. If the virtual machine is started automatically, for
example by a background job scheduler, then it will typically not
have a console.
If this virtual machine has a console then it is represented by a
unique instance of this class which can be obtained by invoking the
System.console()
method. If no console device is
available then an invocation of that method will return null.
Read and write operations are synchronized to guarantee the atomic
completion of critical operations; therefore invoking methods
Console.readLine()
, Console.readPassword()
, format()
,
printf()
as well as the read, format and write operations
on the objects returned by Console.reader()
and Console.writer()
may
block in multithreaded scenarios.
Invoking close() on the objects returned by the Console.reader()
and the Console.writer()
will not close the underlying stream of those
objects.
The console-read methods return null when the end of the
console input stream is reached, for example by typing control-D on
Unix or control-Z on Windows. Subsequent read operations will succeed
if additional characters are later entered on the console's input
device.
Unless otherwise specified, passing a null argument to any method
in this class will cause a NullPointerException
to be thrown.
Security note:
If an application needs to read a password or other secure data, it should
use Console.readPassword()
or Console.readPassword(String, Object...)
and
manually zero the returned character array after processing to minimize the
lifetime of sensitive data in memory.
Console cons;
char[] passwd;
if ((cons = System.console()) != null &&
(passwd = cons.readPassword("[%s]", "Password:")) != null) {
...
java.util.Arrays.fill(passwd, ' ');
}