The Console.java Java example source code
/*
* Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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*/
package java.io;
import java.util.*;
import java.nio.charset.Charset;
import sun.nio.cs.StreamDecoder;
import sun.nio.cs.StreamEncoder;
/**
* Methods to access the character-based console device, if any, associated
* with the current Java virtual machine.
*
* <p> 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.
* <p>
* 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 <tt>null.
* <p>
* 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.
* <p>
* Invoking <tt>close() on the objects returned by the {@link #reader()}
* and the {@link #writer()} will not close the underlying stream of those
* objects.
* <p>
* The console-read methods return <tt>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.
* <p>
* Unless otherwise specified, passing a <tt>null argument to any method
* in this class will cause a {@link NullPointerException} to be thrown.
* <p>
* <b>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.
*
* <blockquote>{@code
* Console cons;
* char[] passwd;
* if ((cons = System.console()) != null &&
* (passwd = cons.readPassword("[%s]", "Password:")) != null) {
* ...
* java.util.Arrays.fill(passwd, ' ');
* }
* }</pre>
*
* @author Xueming Shen
* @since 1.6
*/
public final class Console implements Flushable
{
/**
* Retrieves the unique {@link java.io.PrintWriter PrintWriter} object
* associated with this console.
*
* @return The printwriter associated with this console
*/
public PrintWriter writer() {
return pw;
}
/**
* Retrieves the unique {@link java.io.Reader Reader} object associated
* with this console.
* <p>
* 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 <tt>Scanner:
* <blockquote> * Console con = System.console();
* if (con != null) {
* Scanner sc = new Scanner(con.reader());
* ...
* }
* </pre>
* <p>
* For simple applications requiring only line-oriented reading, use
* <tt>{@link #readLine}.
* <p>
* 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. The {@code Reader}'s {@code read} methods may block if a
* line bound has not been entered or reached on the console's input device.
* A line bound is considered to be any one of a line feed (<tt>'\n'),
* a carriage return (<tt>'\r'), a carriage return followed immediately
* by a linefeed, or an end of stream.
*
* @return The reader associated with this console
*/
public Reader reader() {
return reader;
}
/**
* Writes a formatted string to this console's output stream using
* the specified format string and arguments.
*
* @param fmt
* A format string as described in <a
* href="../util/Formatter.html#syntax">Format string syntax</a>
*
* @param 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
* <cite>The Java™ Virtual Machine Specification.
* The behaviour on a
* <tt>null argument depends on the .
*
* @throws 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 <a
* href="../util/Formatter.html#detail">Details</a> section
* of the formatter class specification.
*
* @return This console
*/
public Console format(String fmt, Object ...args) {
formatter.format(fmt, args).flush();
return this;
}
/**
* A convenience method to write a formatted string to this console's
* output stream using the specified format string and arguments.
*
* <p> An invocation of this method of the form con.printf(format,
* args)</tt> behaves in exactly the same way as the invocation of
* <pre>con.format(format, args).
*
* @param format
* A format string as described in <a
* href="../util/Formatter.html#syntax">Format string syntax</a>.
*
* @param 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
* <cite>The Java™ Virtual Machine Specification.
* The behaviour on a
* <tt>null argument depends on the .
*
* @throws 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 <a
* href="../util/Formatter.html#detail">Details</a> section of the
* formatter class specification.
*
* @return This console
*/
public Console printf(String format, Object ... args) {
return format(format, args);
}
/**
* Provides a formatted prompt, then reads a single line of text from the
* console.
*
* @param fmt
* A format string as described in <a
* href="../util/Formatter.html#syntax">Format string syntax</a>.
*
* @param 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
* <cite>The Java™ Virtual Machine Specification.
*
* @throws 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 <a
* href="../util/Formatter.html#detail">Details</a> section
* of the formatter class specification.
*
* @throws IOError
* If an I/O error occurs.
*
* @return A string containing the line read from the console, not
* including any line-termination characters, or <tt>null
* if an end of stream has been reached.
*/
public String readLine(String fmt, Object ... args) {
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;
}
/**
* Reads a single line of text from the console.
*
* @throws IOError
* If an I/O error occurs.
*
* @return A string containing the line read from the console, not
* including any line-termination characters, or <tt>null
* if an end of stream has been reached.
*/
public String readLine() {
return readLine("");
}
/**
* Provides a formatted prompt, then reads a password or passphrase from
* the console with echoing disabled.
*
* @param fmt
* A format string as described in <a
* href="../util/Formatter.html#syntax">Format string syntax</a>
* for the prompt text.
*
* @param 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
* <cite>The Java™ Virtual Machine Specification.
*
* @throws 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 <a
* href="../util/Formatter.html#detail">Details</a>
* section of the formatter class specification.
*
* @throws IOError
* If an I/O error occurs.
*
* @return A character array containing the password or passphrase read
* from the console, not including any line-termination characters,
* or <tt>null if an end of stream has been reached.
*/
public char[] readPassword(String fmt, Object ... args) {
char[] passwd = null;
synchronized (writeLock) {
synchronized(readLock) {
try {
echoOff = echo(false);
} catch (IOException x) {
throw new IOError(x);
}
IOError ioe = null;
try {
if (fmt.length() != 0)
pw.format(fmt, args);
passwd = readline(true);
} catch (IOException x) {
ioe = new IOError(x);
} finally {
try {
echoOff = echo(true);
} catch (IOException x) {
if (ioe == null)
ioe = new IOError(x);
else
ioe.addSuppressed(x);
}
if (ioe != null)
throw ioe;
}
pw.println();
}
}
return passwd;
}
/**
* Reads a password or passphrase from the console with echoing disabled
*
* @throws IOError
* If an I/O error occurs.
*
* @return A character array containing the password or passphrase read
* from the console, not including any line-termination characters,
* or <tt>null if an end of stream has been reached.
*/
public char[] readPassword() {
return readPassword("");
}
/**
* Flushes the console and forces any buffered output to be written
* immediately .
*/
public void flush() {
pw.flush();
}
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 native String encoding();
private static native boolean echo(boolean on) throws IOException;
private static boolean echoOff;
private char[] readline(boolean zeroOut) throws IOException {
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;
}
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;
}
class LineReader extends Reader {
private Reader in;
private char[] cb;
private int nChars, nextChar;
boolean leftoverLF;
LineReader(Reader in) {
this.in = in;
cb = new char[1024];
nextChar = nChars = 0;
leftoverLF = false;
}
public void close () {}
public boolean ready() throws IOException {
//in.ready synchronizes on readLock already
return in.ready();
}
public int read(char cbuf[], int offset, int length)
throws IOException
{
int off = offset;
int end = offset + length;
if (offset < 0 || offset > cbuf.length || length < 0 ||
end < 0 || end > cbuf.length) {
throw new IndexOutOfBoundsException();
}
synchronized(readLock) {
boolean eof = false;
char c = 0;
for (;;) {
if (nextChar >= nChars) { //fill
int n = 0;
do {
n = in.read(cb, 0, cb.length);
} while (n == 0);
if (n > 0) {
nChars = n;
nextChar = 0;
if (n < cb.length &&
cb[n-1] != '\n' && cb[n-1] != '\r') {
/*
* we're in canonical mode so each "fill" should
* come back with an eol. if there no lf or nl at
* the end of returned bytes we reached an eof.
*/
eof = true;
}
} else { /*EOF*/
if (off - offset == 0)
return -1;
return off - offset;
}
}
if (leftoverLF && cbuf == rcb && cb[nextChar] == '\n') {
/*
* if invoked by our readline, skip the leftover, otherwise
* return the LF.
*/
nextChar++;
}
leftoverLF = false;
while (nextChar < nChars) {
c = cbuf[off++] = cb[nextChar];
cb[nextChar++] = 0;
if (c == '\n') {
return off - offset;
} else if (c == '\r') {
if (off == end) {
/* no space left even the next is LF, so return
* whatever we have if the invoker is not our
* readLine()
*/
if (cbuf == rcb) {
cbuf = grow();
end = cbuf.length;
} else {
leftoverLF = true;
return off - offset;
}
}
if (nextChar == nChars && in.ready()) {
/*
* we have a CR and we reached the end of
* the read in buffer, fill to make sure we
* don't miss a LF, if there is one, it's possible
* that it got cut off during last round reading
* simply because the read in buffer was full.
*/
nChars = in.read(cb, 0, cb.length);
nextChar = 0;
}
if (nextChar < nChars && cb[nextChar] == '\n') {
cbuf[off++] = '\n';
nextChar++;
}
return off - offset;
} else if (off == end) {
if (cbuf == rcb) {
cbuf = grow();
end = cbuf.length;
} else {
return off - offset;
}
}
}
if (eof)
return off - offset;
}
}
}
}
// Set up JavaIOAccess in SharedSecrets
static {
try {
// Add a shutdown hook to restore console's echo state should
// it be necessary.
sun.misc.SharedSecrets.getJavaLangAccess()
.registerShutdownHook(0 /* shutdown hook invocation order */,
false /* only register if shutdown is not in progress */,
new Runnable() {
public void run() {
try {
if (echoOff) {
echo(true);
}
} catch (IOException x) { }
}
});
} catch (IllegalStateException e) {
// shutdown is already in progress and console is first used
// by a shutdown hook
}
sun.misc.SharedSecrets.setJavaIOAccess(new sun.misc.JavaIOAccess() {
public Console console() {
if (istty()) {
if (cons == null)
cons = new Console();
return cons;
}
return null;
}
public Charset charset() {
// This method is called in sun.security.util.Password,
// cons already exists when this method is called
return cons.cs;
}
});
}
private static Console cons;
private native static boolean istty();
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];
}
}
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