Consolepublic final class Console extends Object implements Flushable| 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
{@link java.lang.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
{@link #readLine()}, {@link #readPassword()}, {@link #format format()},
{@link #printf printf()} as well as the read, format and write operations
on the objects returned by {@link #reader()} and {@link #writer()} may
block in multithreaded scenarios.
Invoking close() on the objects returned by the {@link #reader()}
and the {@link #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 {@link NullPointerException} to be thrown.
Security note:
If an application needs to read a password or other secure data, it should
use {@link #readPassword()} or {@link #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, ' ');
}
|
| Fields Summary |
|---|
| private Object | readLock | | private Object | writeLock | | private Reader | reader | | private Writer | out | | private PrintWriter | pw | | private Formatter | formatter | | private Charset | cs | | private char[] | rcb | | private static boolean | echoOff | | private static Console | cons |
| Constructors Summary |
|---|
private Console()
readLock = new Object();
writeLock = new Object();
String csname = encoding();
if (csname != null) {
try {
cs = Charset.forName(csname);
} catch (Exception x) {}
}
if (cs == null)
cs = Charset.defaultCharset();
out = StreamEncoder.forOutputStreamWriter(
new FileOutputStream(FileDescriptor.out),
writeLock,
cs);
pw = new PrintWriter(out, true) { public void close() {} };
formatter = new Formatter(out);
reader = new LineReader(StreamDecoder.forInputStreamReader(
new FileInputStream(FileDescriptor.in),
readLock,
cs));
rcb = new char[1024];
|
| Methods Summary |
|---|
| private static native boolean | echo(boolean on)
| | private static native java.lang.String | encoding()
| | public void | flush()Flushes the console and forces any buffered output to be written
immediately .
pw.flush();
| | public java.io.Console | format(java.lang.String fmt, java.lang.Object args)Writes a formatted string to this console's output stream using
the specified format string and arguments.
formatter.format(fmt, args).flush();
return this;
| | private char[] | grow()
assert Thread.holdsLock(readLock);
char[] t = new char[rcb.length * 2];
System.arraycopy(rcb, 0, t, 0, rcb.length);
rcb = t;
return rcb;
| | private static native boolean | istty()
| | public java.io.Console | printf(java.lang.String format, java.lang.Object args)A convenience method to write a formatted string to this console's
output stream using the specified format string and arguments.
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) .
return format(format, args);
| | public java.lang.String | readLine(java.lang.String fmt, java.lang.Object args)Provides a formatted prompt, then reads a single line of text from the
console.
String line = null;
synchronized (writeLock) {
synchronized(readLock) {
if (fmt.length() != 0)
pw.format(fmt, args);
try {
char[] ca = readline(false);
if (ca != null)
line = new String(ca);
} catch (IOException x) {
throw new IOError(x);
}
}
}
return line;
| | public java.lang.String | readLine()Reads a single line of text from the console.
return readLine("");
| | public char[] | readPassword(java.lang.String fmt, java.lang.Object args)Provides a formatted prompt, then reads a password or passphrase from
the console with echoing disabled.
char[] passwd = null;
synchronized (writeLock) {
synchronized(readLock) {
if (fmt.length() != 0)
pw.format(fmt, args);
try {
echoOff = echo(false);
passwd = readline(true);
} catch (IOException x) {
throw new IOError(x);
} finally {
try {
echoOff = echo(true);
} catch (IOException xx) {}
}
pw.println();
}
}
return passwd;
| | public char[] | readPassword()Reads a password or passphrase from the console with echoing disabled
return readPassword("");
| | public java.io.Reader | reader()Retrieves the unique {@link java.io.Reader Reader} object associated
with this console.
This method is intended to be used by sophisticated applications, for
example, a {@link java.util.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
{@link #readLine}.
The bulk read operations {@link java.io.Reader#read(char[]) read(char[]) },
{@link java.io.Reader#read(char[], int, int) read(char[], int, int) } and
{@link java.io.Reader#read(java.nio.CharBuffer) 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.
return reader;
| | private char[] | readline(boolean zeroOut)
int len = reader.read(rcb, 0, rcb.length);
if (len < 0)
return null; //EOL
if (rcb[len-1] == '\r")
len--; //remove CR at end;
else if (rcb[len-1] == '\n") {
len--; //remove LF at end;
if (len > 0 && rcb[len-1] == '\r")
len--; //remove the CR, if there is one
}
char[] b = new char[len];
if (len > 0) {
System.arraycopy(rcb, 0, b, 0, len);
if (zeroOut) {
Arrays.fill(rcb, 0, len, ' ");
}
}
return b;
| | public java.io.PrintWriter | writer()Retrieves the unique {@link java.io.PrintWriter PrintWriter} object
associated with this console.
return pw;
|
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