public final class Console extends Object implements Flushable
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
readLine(), readPassword(), format(),
printf() as well as the read, format and write operations
on the objects returned by reader() and writer() may
block in multithreaded scenarios.
Invoking close() on the objects returned by the reader()
and the 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 readPassword() or 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, ' ');
}
| Modifier and Type | Class and Description |
|---|---|
(package private) class |
Console.LineReader |
| Modifier and Type | Method and Description |
|---|---|
void |
flush()
Flushes the console and forces any buffered output to be written
immediately .
|
Console |
format(String fmt,
Object... args)
Writes a formatted string to this console's output stream using
the specified format string and arguments.
|
Console |
printf(String format,
Object... args)
A convenience method to write a formatted string to this console's
output stream using the specified format string and arguments.
|
Reader |
reader()
Retrieves the unique
Reader object associated
with this console. |
String |
readLine()
Reads a single line of text from the console.
|
String |
readLine(String fmt,
Object... args)
Provides a formatted prompt, then reads a single line of text from the
console.
|
char[] |
readPassword()
Reads a password or passphrase from the console with echoing disabled
|
char[] |
readPassword(String fmt,
Object... args)
Provides a formatted prompt, then reads a password or passphrase from
the console with echoing disabled.
|
PrintWriter |
writer()
Retrieves the unique
PrintWriter object
associated with this console. |
public PrintWriter writer()
PrintWriter object
associated with this console.public Reader reader()
Reader object associated
with this console.
This method is intended to be used by sophisticated applications, for
example, a Scanner object which utilizes the rich
parsing/scanning functionality provided by the Scanner:
Console con = System.console();
if (con != null) {
Scanner sc = new Scanner(con.reader());
...
}
For simple applications requiring only line-oriented reading, use
readLine(java.lang.String, java.lang.Object...).
The bulk read operations read(char[]) ,
read(char[], int, int) and
read(java.nio.CharBuffer)
on the returned object will not read in characters beyond the line
bound for each invocation, even if the destination buffer has space for
more characters. A line bound is considered to be any one of a line feed
('\n'), a carriage return ('\r'), a carriage return
followed immediately by a linefeed, or an end of stream.
public Console format(String fmt, Object... args)
fmt - A format string as described in Format string syntaxargs - Arguments referenced by the format specifiers in the format
string. If there are more arguments than format specifiers, the
extra arguments are ignored. The number of arguments is
variable and may be zero. The maximum number of arguments is
limited by the maximum dimension of a Java array as defined by
the Java
Virtual Machine Specification. The behaviour on a
null argument depends on the conversion.IllegalFormatException - If a format string contains an illegal syntax, a format
specifier that is incompatible with the given arguments,
insufficient arguments given the format string, or other
illegal conditions. For specification of all possible
formatting errors, see the Details section
of the formatter class specification.public Console printf(String format, Object... args)
An invocation of this method of the form con.printf(format, args) behaves in exactly the same way as the invocation of
con.format(format, args).
format - A format string as described in Format string syntax.args - Arguments referenced by the format specifiers in the format
string. If there are more arguments than format specifiers, the
extra arguments are ignored. The number of arguments is
variable and may be zero. The maximum number of arguments is
limited by the maximum dimension of a Java array as defined by
the Java
Virtual Machine Specification. The behaviour on a
null argument depends on the conversion.IllegalFormatException - If a format string contains an illegal syntax, a format
specifier that is incompatible with the given arguments,
insufficient arguments given the format string, or other
illegal conditions. For specification of all possible
formatting errors, see the Details section of the
formatter class specification.public String readLine(String fmt, Object... args)
fmt - A format string as described in Format string syntax.args - Arguments referenced by the format specifiers in the format
string. If there are more arguments than format specifiers, the
extra arguments are ignored. The maximum number of arguments is
limited by the maximum dimension of a Java array as defined by
the Java
Virtual Machine Specification.IllegalFormatException - If a format string contains an illegal syntax, a format
specifier that is incompatible with the given arguments,
insufficient arguments given the format string, or other
illegal conditions. For specification of all possible
formatting errors, see the Details section
of the formatter class specification.IOError - If an I/O error occurs.public String readLine()
IOError - If an I/O error occurs.public char[] readPassword(String fmt, Object... args)
fmt - A format string as described in Format string syntax
for the prompt text.args - Arguments referenced by the format specifiers in the format
string. If there are more arguments than format specifiers, the
extra arguments are ignored. The maximum number of arguments is
limited by the maximum dimension of a Java array as defined by
the Java
Virtual Machine Specification.IllegalFormatException - If a format string contains an illegal syntax, a format
specifier that is incompatible with the given arguments,
insufficient arguments given the format string, or other
illegal conditions. For specification of all possible
formatting errors, see the Details
section of the formatter class specification.IOError - If an I/O error occurs.public char[] readPassword()
IOError - If an I/O error occurs.