在Java程序中實現高精度列印

在Java環境中,可以使用 java.awt.Toolkit.getScreenResolution()可以得到屏幕每英寸的象素數,但是好像沒有什麼方法能知道某一台印表機的解析度,更別提去控制列印粒度了.於是可恥的使用著醜陋的預設列印精度幾年後,終於找到了解決方法,不知道該高興還是悲傷,其原理說出來也是非常的簡單：

提高列印精度,其實就是把本來是A3紙的內容往A4紙里畫,也就是說,列印區域(這裡對應著Java里的Graphics對象)需要縮小,然後由於預設情況下列印是照72DPI來打的,不做改變的話,列印內容也會跟著變小.這樣就不是我們想要的效果了,還得把列印內容成比例放大.一個縮小,一個放大,於是畫完后,在指定大小的紙張內,便容納了比以往更多象素的內容,這下世界總算完美了.

以上做法形象的說應該是這樣：把需要產生的圖形對象先放大,畫在一張「紙上」,然後整體縮小,這樣精度就提高了.

tips 1：在一般企業報表表格列印中,使用144DPI得到的表格線的寬度看起來最舒服.

tips 2：現在號稱600DPI的印表機其實是576DPI,如果想使用這個解析度的精度,需要用好一點的紙張,已經到極限了,紙張稍差點,列印墨粉就沾不上,導致線體殘缺.

附源碼(修改解析度就改動變數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);

}

}

}

}

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