java - 为什么我的 Java 打印到纸张作业永远不会进入打印机队列？

Question

有很多问题涉及打印机队列中的 PrinterJobs 而不是打印，但我还没有找到有关打印作业永远不会进入队列的讨论。

我的测试程序(参见下面的代码 - 两个类 PrintIt(可打印)和 Report(带有 main 的 jFrame)似乎运行良好，没有异常，但从未将任何内容放入打印队列中。

在代码之后，我将添加正在运行的程序的屏幕截图。

<小时/>

package SVDP;

import java.awt.Graphics;
import java.awt.print.PageFormat;
import java.awt.print.Paper;

/**
 *
 * @author Wesley Stupar
 */
public class Report extends javax.swing.JFrame {

  static Graphics g;
  static Paper pap;
  static PageFormat pf;
  static Report report;
  
  /**
   * Creates new form Report
   */
  public Report() {
    initComponents();
    g = this.getGraphics();
    pap = new Paper();
    pap.setImageableArea(36, 36, 540, 720); //1/2" margins, 8.5x11
    pf = new PageFormat();
    pf.setOrientation(PageFormat.PORTRAIT);
    pf.setPaper(pap);
  }

      /**
   * @param args the command line arguments
   */
  public static void main(String args[]) {
    /* Create and display the form */
    java.awt.EventQueue.invokeLater(new Runnable() {
      public void run() {
        report = new Report();
        report.setVisible(true);
      }
    });
    PrintIt printer = new PrintIt();
    if(g == null){
      System.out.println("Graphics context is null.");
      System.exit(0);
    }
    report.generate();
    try {
System.out.println("Calling print");
      printer.print(g, pf, 0);
    } catch (Exception pe) {
      System.out.println("Printer exception: "+pe);
    }
//    report.setVisible(false);
  }
  
  /**
   * Generate the page to be printed
   */
  public void generate(){
    g.drawString("Hello printer!", 100, 100);    
  }
  // Variables declaration - do not modify                     
  private javax.swing.JPanel jPanel1;
  // End of variables declaration                   
}
--------------------------------------------------------------------
    package SVDP;

import java.awt.print.*;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.print.PageFormat;
import java.awt.print.Printable;
import java.awt.print.PrinterJob;
import javax.print.PrintService;

/**
 *
 * @author Wesley Stupar
 */
public class PrintIt implements Printable {

  PrinterJob job;
  
  public PrintIt() {
    job = PrinterJob.getPrinterJob();
    if (job.printDialog()) {
      try {
        job.print();
      } catch (Exception PrintException) {
        System.out.println("PrintIt exception: "+PrintException);
      }
    }
  }
  
  @Override
    public int print(Graphics g, PageFormat pf, int page) throws
          PrinterException {
      job.setPrintable(this);

      if (page > 0) { /* We have only one page, and 'page' is zero-based */
          return NO_SUCH_PAGE;
      }

      /* User (0,0) is typically outside the imageable area, so we must
       * translate by the X and Y values in the PageFormat to avoid clipping
       */
      Graphics2D g2d = (Graphics2D)g;
      g2d.translate(pf.getImageableX(), pf.getImageableY());

      /* tell the caller that this page is part of the printed document */
System.out.println("Finished print");
      return PAGE_EXISTS;
    }

我不允许发布图像，但我将描述在 NetBeans 下运行的程序所显示的内容:

1. jFrame 与打印对话框重叠显示。所选打印机能够打印测试页。然后对话框就OK了。 NetBeans 输出打印以下内容: 运行: 调用打印 打印完成 构建成功(总时间:12 秒)

程序继续运行，但没有任何内容进入打印队列。该程序必须手动终止。

问题结束。

Answer 1

After looking at this very helpful post:

我发现我试图在可打印之外渲染图像，并且没有正确实例化可打印。