The selected printer when the dialog is initially displayed will reflect the print service currently attached to this print job. If the user changes the print service, the PrinterJob will be updated to reflect this, unless the user cancels the dialog. As well as allowing the user to select the destination printer, the user can also select values of various print request attributes. The attributes parameter on input will reflect the applications required initial selections in the user dialog. Attributes not specified display using the default for the service.

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Headless mode is a system configuration in which the display device, keyboard, or mouse is lacking. Sounds unexpected, but actually you can perform different operations in this mode, even with graphic data. Where it is applicable? When creating an image, your application needs neither the display nor the keyboard.

An image that was generated in the headless mode system then can be passed to the headful system for further rendering. Note: This article will point the reader to documentation for version 6 of the Java SE platform.

Toolkit The java. Subclasses of Toolkit are used to bind the various AWT components to particular native toolkit implementations. Many components are affected if a display device, keyboard, or mouse is not supported. An appropriate class constructor throws a HeadlessException : Such heavyweight components require a peer at the operating-system level, which cannot be guaranteed on headless machines. Methods related to Canvas, Panel, and Image components do not need to throw a HeadlessException because these components can be given empty peers and treated as lightweight components.

Graphics Environment The java. GraphicsEnvironment class is an abstract class that describes the collection of GraphicsDevice objects and Font objects available to a Java technology application on a particular platform. The resources in this GraphicsEnvironment might be local or on a remote machine. GraphicsDevice objects can be monitors, printers, or image buffers and are the destination of Graphics2D drawing methods.

Each GraphicsDevice has many GraphicsConfiguration objects associated with it. These objects specify the different configurations in which the GraphicsDevice can be used. Table 1 shows the GraphicsEnvironment methods that check for headless mode support. Table 1. The Headless Mode Methods Method public static boolean isHeadless Tests whether the environment is headless, and therefore does not support a display device, keyboard, or mouse.

If this method returns true, a HeadlessException is thrown from areas of the Toolkit and GraphicsEnvironment classes that depend on a display device, keyboard, or mouse. If this method returns true, a HeadlessException is thrown from areas of the GraphicsEnvironment that depend on a display device, keyboard, or mouse.

Note: The isHeadless method checks the specific system property, java. A HeadlessException is thrown when code that depends on a display device, keyboard, or mouse is called in an environment that does not support any of these.

The exception is derived from an UnsupportedOperationException, which is itself derived from a RuntimeException. Setting Up Headless Mode To use headless mode operations, you must first understand how to check and set up the system properties related to this mode.

In addition, you must understand how to create a default toolkit to use the headless implementation of the Toolkit class. System Properties Setup To set up headless mode, set the appropriate system property by using the setProperty method.

This method enables you to set the desired value for the system property that is indicated by the specific key. You can also use the following command line if you plan to run the same application in both a headless and a traditional environment: java -Djava.


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