Summary

Provide a mechanism for enabling alternative java.io.Console implementations within the JDK.

Problem

java.io.Console instance is only available when the JVM is attached to an OS provided interactive console. Otherwise System.console() returns null. This is not very useful for applications such as jshell in which the debugee process is not attached to a console.

Solution

Provide a means to utilize alternative Console implementations within the JDK. Those alternative implementations of Console may be returned with System.console() even when the JVM is not attached to the underlying platform's TTY. This also allows replacing the default Console implementation with functionality-rich jline.

The alternative Console implementation is searched using ServiceLoader with non-public jdk.internal.io.JdkConsoleProvider interface. A new non-public system property jdk.console designates the module name which the System.console() returns the implementation. jdk.internal.le and jdk.jshell are only allowed to provide the implementation for security purposes. The Console implementation based on jline is the default Console if the jdk.internal.le module is available. The following chart depicts which instance is returned from System.console() call:

Specifying thejdk.console system property overrides the above default, ie.,

-Djdk.console=jdk.jshell

will look for the implementation in jdk.jshell module. If there is one, the above default Console will be replaced with the one in jdk.jshell module.

Specification

Remove final from the class definition of java.io.Console class in order for creating a proxying subclass of it.