用 Java 保存位图文件

FFFF FFFF FFFF FFFF FFFF
0000000100 FFFF FFFF FFFF FFFF FFFF FFFF FFFF FFFF
*

在，我们开始检视代码

　　现在我们已经知道了 24 位位图文件的结构，下面就是您期待已久的内容：用来将图像对象写入位图文件的代码。
import java.awt.*;
import java.io.*;
import java.awt.image.*;

public class BMPFile extends Component {

file://--- 私有常量
private final static int BITMAPFILEHEADER_SIZE = 14;
private final static int BITMAPINFOHEADER_SIZE = 40;

file://--- 私有变量声明

file://--- 位图文件标头
private byte bitmapFileHeader [] = new byte [14];
private byte bfType [] = {'B', 'M'};
private int bfSize = 0;
private int bfReserved1 = 0;
private int bfReserved2 = 0;
private int bfOffBits = BITMAPFILEHEADER_SIZE + BITMAPINFOHEADER_SIZE;

file://--- 位图信息标头
private byte bitmapInfoHeader [] = new byte [40];
private int biSize = BITMAPINFOHEADER_SIZE;
private int biWidth = 0;
private int biHeight = 0;
private int biPlanes = 1;
private int biBitCount = 24;
private int biCompression = 0;
private int biSizeImage = 0x030000;
private int biXPelsPerMeter = 0x0;
private int biYPelsPerMeter = 0x0;
private int biClrUsed = 0;
private int biClrImportant = 0;

file://--- 位图原始数据
private int bitmap [];

file://--- 文件部分
private FileOutputStream fo;

file://--- 缺省构造函数
public BMPFile() {

}


public void saveBitmap (String parFilename, Image parImage, int
parWidth, int parHeight) {

try {
fo = new FileOutputStream (parFilename);
save (parImage, parWidth, parHeight);
fo.close ();
}
catch (Exception saveEx) {
saveEx.printStackTrace ();
}

}


/*
* saveMethod 是该进程的主方法。该方法
* 将调用 convertImage 方法以将内存图像转换为
* 字节数组；writeBitmapFileHeader 方法创建并写入
* 位图文件标头；writeBitmapInfoHeader 创建
* 信息标头；writeBitmap 写入图像。
*
*/
private void save (Image parImage, int parWidth, int parHeight) {

try {
convertImage (parImage, parWidth, parHeight);
writeBitmapFileHeader ();
writeBitmapInfoHeader ();
writeBitmap ();
}
catch (Exception saveEx) {
saveEx.printStackTrace ();
}
}


/*
* convertImage 将内存图像转换为位图格式 (BRG)。
* 它还计算位图信息标头所用的某些信息。
*
*/
private boolean convertImage (Image parImage, int parWidth, int parHeight) {

int pad;
bitmap = new int [parWidth * parHeight];

PixelGrabber pg = new PixelGrabber (parImage, 0, 0, parWidth, parHeight,
bitmap, 0, parWidth);

try {
pg.grabPixels ();
}
catch (InterruptedException e) {
e.printStackTrace ();
return (false);
}

pad = (4 - ((parWidth * 3) % 4)) * parHeight;
biSizeImage = ((parWidth * parHeight) * 3) + pad;
bfSize = biSizeImage + BITMAPFILEHEADER_SIZE +
BITMAPINFOHEADER_SIZE;
biWidth = parWidth;
biHeight = parHeight;

return (true);
}

/*
* writeBitmap 将象素捕获器返回的图像转换为
* 所需的格式。请记住：扫描行在位图文件中是
* 反向存储的！
*
* 每个扫描行必须补足为 4 个字节。
*/
private void writeBitmap () {

int size;
int value;
int j;
int i;
int rowCount;
int rowIndex;
int lastRowIndex;
int pad;
int padCount;
byte rgb [] = new byte [3];


size = (biWidth * biHeight) - 1;
pad = 4 - ((biWidth * 3) % 4);
if (pad == 4) // <==== 错误修正
pad = 0; // <==== 错误修正
rowCount = 1;
padCount = 0;
rowIndex = size - biWidth;
lastRowIndex = rowIndex;

try {
for (j = 0; j < size; j++) {
value = bitmap [rowIndex];
rgb [0] = (byte) (value & 0xFF);
rgb [1] = (byte) ((value >> 8) & 0xFF);
rgb [2] = (byte) ((value >> 16) & 0xFF);
fo.write (rgb);
if (rowCount == biWidth) {
padCount += pad;
for (i = 1; i <= pad; i++) {
fo.write (0x00);
}
rowCount = 1;
rowIndex = lastRowIndex - biWidth;
lastRowIndex = rowIndex;
}
else
rowCount++;
rowIndex++;
}

file://--- 更新文件大小
bfSize += padCount - pad;
biSizeImage += padCount - pad;
}
catch (Exception wb) {
wb.printStackTrace ();
}

}

/*
* writeBitmapFileHeader 将位图文件标头写入文件中。
*
*/
private void writeBitmapFileHeader () {

try {
fo.write (bfType);
fo.write (intToDWord (bfSize));
fo.write (intToWord (bfReserved1));
fo.write (intToWord (bfReserved2));
fo.write (intToDWord (bfOffBits));

}
catch (Exception wbfh) {
wbfh.printStackTrace ();
}

}

/*
*
* writeBitmapInfoHeader 将位图信息标头
* 写入文件中。
*
*/

private void writeBitmapInfoHeader () {

try {
fo.write (intToDWord (biSize));
fo.write (intToDWord (biWidth));
fo.write (intToDWord (biHeight));
fo.write (intToWord (biPlanes));
fo.write (intToWord (biBitCount));
fo.write (intToDWord (biCompression));
fo.write (intToDWord (biSizeImage));
fo.write (intToDWord (biXPelsPerMeter));
fo.write (intToDWord (biYPelsPerMeter));
fo.write (intToDWord (biClrUsed));
fo.write (intToDWord (biClrImportant));
}
catch (Exception wbih) {
wbih.printStackTrace ();
}

}


/*
*
* intToWord 将整数转换为单字，返回值
* 存储在一个双字节数组中。
*
*/
private byte [] intToWord (int parValue) {

byte retValue [] = new byte [2];

retValue [0] = (byte) (parValue & 0x00FF);
retValue [1] = (byte) ((parValue >> 8) & 0x00FF);

return (retValue);

}

/*
*
* intToDWord 将整数转换为双字，返回值
* 存储在一个 4 字节数组中。
*
*/
private byte [] intToDWord (int parValue) {

byte retValue [] = new byte [4];

retValue [0] = (byte) (parValue & 0x00FF);
retValue [1] = (byte) ((parValue >> 8) & 0x000000FF);
retValue [2] = (byte) ((parValue >> 16) & 0x000000FF);
retValue [3] = (byte) ((parValue >> 24) & 0x000000FF);

return (retValue);

}

}


　　小结

　　这就是所要做的全部工作。我确信您将会发现这个类很有用，因为到 JDK 1.1.6 为止，Java 不支持用任何常用的格式保存图像。JDK 1.2 将支持创建 JPEG 图像，但不支持创建位图。所以这个类仍将填补 JDK1.2 中的空白。

……