在java环境中,可以使用 java.awt.Toolkit.getScreenResolution()可以得到屏幕每英寸的象素数,但是似乎没有什么方法能知道某一台打印机的分辨率,更别提去控制打印粒度了。于是可耻的使用着丑陋的缺省打印精度几年后,终于找到了解决方法,不知道该兴奋还是悲伤,其原理说出来也是非常的简单:
提高打印精度,其实就是把本来是A3纸的内容往A4纸里画,也就是说,打印区域(这里对应着Java里的Graphics对象)需要缩小,然后由于缺省情况下打印是照72DPI来打的,不做改变的话,打印内容也会跟着变小。这样就不是我们想要的效果了,所以还得把打印内容成比例放大。一个缩小,一个放大,于是画完后,在指定大小的纸张内,便容纳了比以往更多象素的内容,这下世界总算完美了。
以上做法形象的说应该是这样:把需要产生的图形对象先放大,画在一张“纸上”,然后整体缩小,这样精度就提高了。
tips 1:在一般企业报表表格打印中,使用144DPI得到的表格线的宽度看起来最舒适。
tips 2:现在号称600DPI的打印机其实是576DPI,假如想使用这个分辨率的精度,需要用好一点的纸张,因为已经到极限了,纸张稍差点,打印墨粉就沾不上,导致线体残缺。
附源码(修改分辨率就改动变量iResMul就好):
import java.awt.*;import java.awt.PRint.*;public class MyPrintableObject implements Printable { public int iResMul = 1; // 1 = 72 dpi; 4 = 288 dpi public int print(Graphics g, PageFormat pf, int iPage) throws PrinterException { final int FONTSIZE = 12; final double PNT_MM = 25.4 / 72.; if (0 != iPage) return NO_SUCH_PAGE; try { int iPosX = 1; int iPosY = 1; int iAddY = FONTSIZE * 3 / 2 * iResMul; int iWdth = (int) Math.round(pf.getImageableWidth() * iResMul) - 3; int iHght = (int) Math.round(pf.getImageableHeight() * iResMul) - 3; int iCrcl = Math.min(iWdth, iHght) - 4 * iResMul; Graphics2D g2 = (Graphics2D) g; PrinterJob prjob = ((PrinterGraphics) g2).getPrinterJob(); g2.translate(pf.getImageableX(), pf.getImageableY()); g2.scale(1.0 / iResMul, 1.0 / iResMul); g2.setFont(new Font("SansSerif", Font.PLAIN, FONTSIZE * iResMul)); g2.setColor(Color.black); g2.drawRect(iPosX, iPosY, iWdth, iHght); g2.drawLine(iPosX, iHght / 2 + iWdth / 50, iPosX + iWdth, iHght / 2 - iWdth / 50); g2.drawLine(iPosX, iHght / 2 - iWdth / 50, iPosX + iWdth, iHght / 2 + iWdth / 50); g2.drawOval(iPosX + 2 * iResMul, iHght - iCrcl - 2 * iResMul, iCrcl, iCrcl); iPosX += iAddY; iPosY += iAddY / 2; g2.drawString("PrinterJob-UserName: " + prjob.getUserName(), iPosX, iPosY += iAddY); g2.drawString("Betriebssystem: " + System.getProperty("os.name") + " " + System.getProperty("os.version"), iPosX, iPosY += iAddY); g2 .drawString("Java-Version: JDK " + System.getProperty("java.version"), iPosX, iPosY += iAddY); g2.drawString("Width/Height: " + dbldgt(pf.getWidth()) + " / " + dbldgt(pf.getHeight()) + " points = " + dbldgt(pf.getWidth() * PNT_MM) + " / " + dbldgt(pf.getHeight() * PNT_MM) + " mm", iPosX, iPosY += iAddY); g2.drawString("Imageable Width/Height: " + dbldgt(pf.getImageableWidth()) + " / " + dbldgt(pf.getImageableHeight()) + " points = " + dbldgt(pf.getImageableWidth() * PNT_MM) + " / " + dbldgt(pf.getImageableHeight() * PNT_MM) + " mm", iPosX, iPosY += iAddY); g2.drawString("Imageable X/Y: " + dbldgt(pf.getImageableX()) + " / " + dbldgt(pf.getImageableY()) + " points = " + dbldgt(pf.getImageableX() * PNT_MM) + " / " + dbldgt(pf.getImageableY() * PNT_MM) + " mm", iPosX, iPosY += iAddY); g2.drawString("versuchte Druckaufl sung: " + 72 * iResMul + " dpi", iPosX, iPosY += iAddY); } catch (Exception ex) { throw new PrinterException(ex.getMessage()); } return PAGE_EXISTS; } private static double dbldgt(double d) { return Math.round(d * 10.) / 10.; // show one digit after point } public static void main(String[] args) { PrinterJob pj = PrinterJob.getPrinterJob(); pj.setPrintable(new MyPrintableObject()); if (pj.printDialog()) { try { pj.print(); } catch (PrinterException e) { System.out.println(e); } } }}