Summary

Make JLine the default Console provider

Problem

The initial intention for using JLine module for the Console was for a better user experience (JDK-8295803). However, the implementation was spawning native OS commands in Linux/macOS environments and caused performance degradation on some app's startup time (JDK-8299137), thus the use of JLine was made optional (JDK-8299689) for Console. So unless the user opt-in for using JLine via the system property, Console defaults to the built-in implementation.

Solution

JLine implementation no longer spawns native commands with the fix to JDK-8306983, it is desirable to make the JLine implementation the default Console provider. By lazily instantiating JLine instance, the performance regression can be improved down from >4% (as in JDK-8299137) to 2%. Also, introduce a new public method for applications which need to know whether the Console instance is a TTY environment or not, which has been simulated by System.console() != null.

Specification

Add the following new public method in java.io.Console class:

 /**
  * {@return if the {@code Console} instance is a terminal}
  * <p>
  * 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()