Java system console readline

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 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)

Method Summary

Writes a formatted string to this console’s output stream using the specified format string and arguments.

A convenience method to write a formatted string to this console’s output stream using the specified format string and arguments.

Provides a formatted prompt, then reads a password or passphrase from the console with echoing disabled.

Methods declared in class java.lang.Object

Method Detail

writer

reader

Retrieves the unique 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)

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. The Reader ‘s 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 ( ‘\n’ ), a carriage return ( ‘\r’ ), a carriage return followed immediately by a linefeed, or an end of stream.

format

public Console format(String fmt, Object. args)

Writes a formatted string to this console’s output stream using the specified format string and arguments.

printf

public 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. An invocation of this method of the form con.printf(format, args) behaves in exactly the same way as the invocation of

readLine

public String readLine(String fmt, Object. args)

readLine

readPassword

Provides a formatted prompt, then reads a password or passphrase from the console with echoing disabled.

readPassword

flush

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Java system console readline

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 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)

Method Summary

Writes a formatted string to this console’s output stream using the specified format string and arguments.

A convenience method to write a formatted string to this console’s output stream using the specified format string and arguments.

Provides a formatted prompt, then reads a password or passphrase from the console with echoing disabled.

Methods inherited from class java.lang.Object

Method Detail

writer

reader

Console con = System.console(); if (con != null)

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. The Reader ‘s 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 ('\n'), a carriage return ('\r'), a carriage return followed immediately by a linefeed, or an end of stream.

format

public Console format(String fmt, Object. args)

Writes a formatted string to this console’s output stream using the specified format string and arguments.

printf

public 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. An invocation of this method of the form con.printf(format, args) behaves in exactly the same way as the invocation of

readLine

public String readLine(String fmt, Object. args)

readLine

readPassword

Provides a formatted prompt, then reads a password or passphrase from the console with echoing disabled.

readPassword

flush

Источник

Class Console

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 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 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)

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