Java SE上使用Headless模式 在Java SE上使用Headless模式的超级指南

System.setProperty("java.awt.headless", "true");

java -Djava.awt.headless=true 

Toolkit tk = Toolkit.getDefaultToolkit();

GraphicsEnvironment ge =
GraphicsEnvironment.getLocalGraphicsEnvironment();
boolean headless_check = ge.isHeadless();

final Canvas c = new Canvas()
{
  public void paint(Graphics g)
  {
    Rectangle r = getBounds();
    g.drawLine(0, 0, r.width - 1, r.height - 1);
    g.drawLine(0, r.height - 1, r.width - 1, 0);
  }
};

public void paint(Graphics g)
{
 g.setFont(new Font("Arial", Font.ITALIC, 12));
 g.drawString("Test", 32, 8);
}

public void paint(Graphics g)
{
 g.setColor(new Color(255, 127, 0));
 g.drawLine(0, r.height - 1, r.width - 1, 0);
}

Image i = null;
try
{
 File f = new File("grapefruit.jpg");
 i = ImageIO.read(f);
}
catch (Exception z)
{
 z.printStackTrace(System.err);
}

PrinterJob pj = PrinterJob.getPrinterJob();
pj.setPrintable(new Printable()
{
 public int print(Graphics g, PageFormat pf, int pageIndex)
 {
  if (pageIndex > 0)
  {
   return Printable.NO_SUCH_PAGE;
  }
 
  ((Graphics2D)g).translate(pf.getImageableX(),
         pf.getImageableY());
 
  // Paint canvas.
  c.paint(g);
 
  return Printable.PAGE_EXISTS;
 }
});

Toolkit tk = Toolkit.getDefaultToolkit();
tk.beep();

import java.awt.*;
import java.io.*;
import java.awt.print.*;
 
import javax.imageio.*;
 
public class HeadlessBasics
{
 public static void main(String[] args)
 {
  // Set system property.
  // Call this BEFORE the toolkit has been initialized, that is,
  // before Toolkit.getDefaultToolkit() has been called.
  System.setProperty("java.awt.headless", "true");
 
  // This triggers creation of the toolkit.
  // Because java.awt.headless property is set to true, this
  // will be an instance of headless toolkit.
  Toolkit tk = Toolkit.getDefaultToolkit();
  // Standard beep is available.
  tk.beep();
 
  // Check whether the application is
  // running in headless mode.
  GraphicsEnvironment ge =
  GraphicsEnvironment.getLocalGraphicsEnvironment();
  System.out.println("Headless mode: " + ge.isHeadless());
 
  // No top levels are allowed.
  boolean created = false;
  try
  {
   Frame f = new Frame("Frame");
   created = true;
  }
  catch (Exception z)
  {
   z.printStackTrace(System.err);
   created = false;
  }
  System.err.println("Frame is created: " + created);
 
  // No other components except Canvas and Panel are allowed.
  created = false;
  try
  {
   Button b = new Button("Button");
   created = true;
  }
  catch (Exception z)
  {
   z.printStackTrace(System.err);
   created = false;
  }
  System.err.println("Button is created: " + created);
   
  // Canvases can be created.
  final Canvas c = new Canvas()
  {
   public void paint(Graphics g)
   {
    Rectangle r = getBounds();
    g.drawLine(0, 0, r.width - 1, r.height - 1);
    // Colors work too.
    g.setColor(new Color(255, 127, 0));
    g.drawLine(0, r.height - 1, r.width - 1, 0);
    // And fonts
    g.setFont(new Font("Arial", Font.ITALIC, 12));
    g.drawString("Test", 32, 8);
   }
  };
  // And all the operations work correctly.
  c.setBounds(32, 32, 128, 128);
 
  // Images are available.
  Image i = null;
  try
  {
   File f = new File("grapefruit.jpg");
   i = ImageIO.read(f);
  }
  catch (Exception z)
  {
   z.printStackTrace(System.err);
  }
  final Image im = i;
   
  // Print system is available.
  PrinterJob pj = PrinterJob.getPrinterJob();
  pj.setPrintable(new Printable()
  {
   public int print(Graphics g, PageFormat pf, int pageIndex)
   {
    if (pageIndex > 0)
    {
     return Printable.NO_SUCH_PAGE;
    }
    ((Graphics2D)g).translate(pf.getImageableX(),
           pf.getImageableY());
 
    // Paint the canvas.
    c.paint(g);
 
    // Paint the image.
    if (im != null)
    {
     g.drawImage(im, 32, 32, 64, 64, null);
    }
 
    return Printable.PAGE_EXISTS;
   }
  });
  try
  {
   pj.print();
  }
  catch (Exception z)
  {
   z.printStackTrace(System.err);
  }
 }
}

Headless mode: true
java.awt.HeadlessException
at java.awt.GraphicsEnvironment.checkHeadless(Unknown Source)
at java.awt.Window.<init>(Unknown Source)
at java.awt.Frame.<init>(Unknown Source)
at HeadlessBasics.main(HeadlessBasics.java:24)
Frame is created: false
java.awt.HeadlessException
at java.awt.GraphicsEnvironment.checkHeadless(Unknown Source)
at java.awt.Button.<init>(Unknown Source)
at HeadlessBasics.main(HeadlessBasics.java:39)
Button is created: false

java HeadlessBasics 2> standard_output.txt