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 may 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 {@code 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. *
* Operations that format strings are locale sensitive, using either the * specified {@code Locale}, or the * {@link Locale##default_locale default format Locale} to produce localized * formatted strings. *
* Invoking {@code 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 {@code 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 {@code 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. * * {@snippet lang=java : * Console cons; * char[] passwd; * if ((cons = System.console()) != null && * (passwd = cons.readPassword("[%s]", "Password:")) != null) { * ... * java.util.Arrays.fill(passwd, ' '); * } * } * * @author Xueming Shen * @since 1.6 */ public sealed class Console implements Flushable permits ProxyingConsole { /** * Package private no-arg constructor. */ Console() {} /** * Retrieves the unique {@link java.io.PrintWriter PrintWriter} object * associated with this console. * * @return The printwriter associated with this console */ public PrintWriter writer() { throw newUnsupportedOperationException(); } /** * 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 {@code Scanner}: * {@snippet lang=java : * Console con = System.console(); * if (con != null) { * Scanner sc = new Scanner(con.reader()); * code: // @replace substring="code:" replacement="..." * } * } *
* 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. 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 ({@code '\n'}), * a carriage return ({@code '\r'}), a carriage return followed immediately * by a linefeed, or an end of stream. * * @return The reader associated with this console */ public Reader reader() { throw newUnsupportedOperationException(); } /** * Writes a string representation of the specified object to this console's * output stream, terminates the line using {@link System#lineSeparator()} * and then flushes the console. * *
The string representation of the specified object is obtained as if * by calling {@link String#valueOf(Object)}. * * @param obj * An object whose string representation is to be written, * may be {@code null}. * * @return This console * * @since 23 */ @PreviewFeature(feature = PreviewFeature.Feature.IMPLICIT_CLASSES) public Console println(Object obj) { throw newUnsupportedOperationException(); } /** * Terminates the current line in this console's output stream using * {@link System#lineSeparator()} and then flushes the console. * * @return This console * * @since 24 */ @PreviewFeature(feature = PreviewFeature.Feature.IMPLICIT_CLASSES) public Console println() { return println(""); } /** * Writes a string representation of the specified object to this console's * output stream and then flushes the console. * *
The string representation of the specified object is obtained as if * by calling {@link String#valueOf(Object)}. * * @param obj * An object whose string representation is to be written, * may be {@code null}. * * @return This console * * @since 23 */ @PreviewFeature(feature = PreviewFeature.Feature.IMPLICIT_CLASSES) public Console print(Object obj) { throw newUnsupportedOperationException(); } /** * Writes a prompt as if by calling {@code print}, then reads a single line * of text from this console. * * @param prompt * A prompt string, may be {@code null}. * * @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 {@code null} * if an end of stream has been reached without having read * any characters. * * @since 23 */ @PreviewFeature(feature = PreviewFeature.Feature.IMPLICIT_CLASSES) public String readln(String prompt) { throw newUnsupportedOperationException(); } /** * Reads a single line of text from this 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 {@code null} * if an end of stream has been reached without having read * any characters. * * @since 24 */ @PreviewFeature(feature = PreviewFeature.Feature.IMPLICIT_CLASSES) public String readln() { throw newUnsupportedOperationException(); } /** * Writes a formatted string to this console's output stream using * the specified format string and arguments with the * {@link Locale##default_locale default format locale}. * * @param format * A format string as described in {@link * Formatter##syntax Format string syntax}. * * @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 * The Java Virtual Machine Specification. * The behavior on a * {@code null} argument depends on the {@link * Formatter##syntax conversion}. * * @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 {@link * Formatter##detail Details} section * of the formatter class specification. * * @return This console */ public Console format(String format, Object ... args) { throw newUnsupportedOperationException(); } /** * Writes a formatted string to this console's output stream using * the specified format string and arguments with the specified * {@code locale}. * * @param locale The {@linkplain Locale locale} to apply during * formatting. If {@code locale} is {@code null} then no localization * is applied. * * @param format * A format string as described in {@link * Formatter##syntax Format string syntax}. * * @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 * The Java Virtual Machine Specification. * The behavior on a * {@code null} argument depends on the {@link * Formatter##syntax conversion}. * * @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 {@link * Formatter##detail Details} section * of the formatter class specification. * * @return This console * @since 23 */ public Console format(Locale locale, String format, Object ... args) { throw newUnsupportedOperationException(); } /** * A convenience method to write a formatted string to this console's * output stream using the specified format string and arguments with * the {@link Locale##default_locale default format locale}. * * @implSpec This is the same as calling {@code format(format, args)}. * * @param format * A format string as described in {@link * Formatter##syntax Format string syntax}. * * @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 * The Java Virtual Machine Specification. * The behavior on a * {@code null} argument depends on the {@link * Formatter##syntax conversion}. * * @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 {@link * Formatter##detail Details} section of the * formatter class specification. * * @return This console */ public Console printf(String format, Object ... args) { throw newUnsupportedOperationException(); } /** * A convenience method to write a formatted string to this console's * output stream using the specified format string and arguments with * the specified {@code locale}. * * @implSpec This is the same as calling * {@code format(locale, format, args)}. * * @param locale The {@linkplain Locale locale} to apply during * formatting. If {@code locale} is {@code null} then no localization * is applied. * * @param format * A format string as described in {@link * Formatter##syntax Format string syntax}. * * @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 * The Java Virtual Machine Specification. * The behavior on a * {@code null} argument depends on the {@link * Formatter##syntax conversion}. * * @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 {@link * Formatter##detail Details} section of the * formatter class specification. * * @return This console * @since 23 */ public Console printf(Locale locale, String format, Object ... args) { throw newUnsupportedOperationException(); } /** * Provides a formatted prompt using the * {@link Locale##default_locale default format locale}, then reads a * single line of text from the console. * * @param format * A format string as described in {@link * Formatter##syntax Format string syntax}. * * @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 * The Java Virtual Machine Specification. * The behavior on a * {@code null} argument depends on the {@link * Formatter##syntax conversion}. * * @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 {@link * Formatter##detail Details} 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 {@code null} * if an end of stream has been reached. */ public String readLine(String format, Object ... args) { throw newUnsupportedOperationException(); } /** * Provides a formatted prompt using the specified {@code locale}, then * reads a single line of text from the console. * * @param locale The {@linkplain Locale locale} to apply during * formatting. If {@code locale} is {@code null} then no localization * is applied. * * @param format * A format string as described in {@link * Formatter##syntax Format string syntax}. * * @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 * The Java Virtual Machine Specification. * The behavior on a * {@code null} argument depends on the {@link * Formatter##syntax conversion}. * * @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 {@link * Formatter##detail Details} 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 {@code null} * if an end of stream has been reached. * @since 23 */ public String readLine(Locale locale, String format, Object ... args) { throw newUnsupportedOperationException(); } /** * 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 {@code null} * if an end of stream has been reached. */ public String readLine() { throw newUnsupportedOperationException(); } /** * Provides a formatted prompt using the * {@link Locale##default_locale default format locale}, then reads a * password or passphrase from the console with echoing disabled. * * @param format * A format string as described in {@link * Formatter##syntax Format string syntax} * 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 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 behavior on a * {@code null} argument depends on the {@link * Formatter##syntax conversion}. * * @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 {@link * Formatter##detail Details} 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 {@code null} if an end of stream has been reached. */ public char[] readPassword(String format, Object ... args) { throw newUnsupportedOperationException(); } /** * Provides a formatted prompt using the specified {@code locale}, then * reads a password or passphrase from the console with echoing disabled. * * @param locale The {@linkplain Locale locale} to apply during * formatting. If {@code locale} is {@code null} then no localization * is applied. * * @param format * A format string as described in {@link * Formatter##syntax Format string syntax} * 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 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 behavior on a * {@code null} argument depends on the {@link * Formatter##syntax conversion}. * * @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 {@link * Formatter##detail Details} 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 {@code null} if an end of stream has been reached. * @since 23 */ public char[] readPassword(Locale locale, String format, Object ... args) { throw newUnsupportedOperationException(); } /** * 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 {@code null} if an end of stream has been reached. */ public char[] readPassword() { throw newUnsupportedOperationException(); } /** * Flushes the console and forces any buffered output to be written * immediately. */ public void flush() { throw newUnsupportedOperationException(); } /** * Returns the {@link java.nio.charset.Charset Charset} object used for * the {@code Console}. *
* The returned charset corresponds to the input and output source * (e.g., keyboard and/or display) specified by the host environment or user, * which defaults to the one based on {@link System##stdout.encoding stdout.encoding}. * It may not necessarily be the same as the default charset returned from * {@link java.nio.charset.Charset#defaultCharset() Charset.defaultCharset()}. * * @return a {@link java.nio.charset.Charset Charset} object used for the * {@code Console} * @since 17 */ public Charset charset() { throw newUnsupportedOperationException(); } /** * {@return {@code true} if the {@code Console} instance is a terminal} *
* This method returns {@code true} if the console device, associated with the current * Java virtual machine, is a terminal, typically an interactive command line * connected to a keyboard and display. * * @implNote The default implementation returns the value equivalent to calling * {@code isatty(stdin/stdout)} on POSIX platforms, or whether standard in/out file * descriptors are character devices or not on Windows. * * @since 22 */ public boolean isTerminal() { return istty; } private static UnsupportedOperationException newUnsupportedOperationException() { return new UnsupportedOperationException( "Console class itself does not provide implementation"); } private static final boolean istty = istty(); static final Charset CHARSET = Charset.forName(System.getProperty("stdout.encoding"), UTF_8.INSTANCE); private static final Console cons = instantiateConsole(); static { // Set up JavaIOAccess in SharedSecrets SharedSecrets.setJavaIOAccess(new JavaIOAccess() { public Console console() { return cons; } }); } private static Console instantiateConsole() { Console c = null; try { /* * The JdkConsole provider used for Console instantiation can be specified * with the system property "jdk.console", whose value designates the module * name of the implementation, and which defaults to the value of * {@code JdkConsoleProvider.DEFAULT_PROVIDER_MODULE_NAME}. If multiple * provider implementations exist in that module, the first one found is used. * If no providers are available, or instantiation failed, java.base built-in * Console implementation is used. */ var consModName = System.getProperty("jdk.console", JdkConsoleProvider.DEFAULT_PROVIDER_MODULE_NAME); for (var jcp : ServiceLoader.load(ModuleLayer.boot(), JdkConsoleProvider.class)) { if (consModName.equals(jcp.getClass().getModule().getName())) { var jc = jcp.console(istty, CHARSET); if (jc != null) { c = new ProxyingConsole(jc); } break; } } } catch (ServiceConfigurationError _) { } // If not found, default to built-in Console if (istty && c == null) { c = new ProxyingConsole(new JdkConsoleImpl(CHARSET)); } return c; } private static native boolean istty(); }