/**
* 接口设计
*/
public interface ImageDPIProcessor {
/**
* 根据文件后缀扩展名判断是否能进行处理
*
* @param fileName
* @return
*/
public boolean canHandle(String fileName);
/**
*
* @param path
* @param dpi
* dot per inch
* @return
* @throws IOException
* @throws MalformedURLException
*/
public byte[] process(final BufferedImage srcimage, final int dpi) throws Exception;
JPEG 处理方式
public class JpegDPIProcessor implements ImageDPIProcessor {
private String formatName = "jpeg";
@Override
public byte[] process(BufferedImage image, int dpi) throws IOException {
for (Iterator<ImageWriter> iw = ImageIO.getImageWritersByFormatName(formatName); iw.hasNext();) {
ImageWriter writer = iw.next();
ImageWriteParam writeParams = writer.getDefaultWriteParam();
writeParams.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
//调整图片质量
writeParams.setCompressionQuality(1f);
IIOMetadata data = writer.getDefaultImageMetadata(new ImageTypeSpecifier(image), writeParams);
Element tree = (Element) data.getAsTree("javax_imageio_jpeg_image_1.0");
Element jfif = (Element) tree.getElementsByTagName("app0JFIF").item(0);
jfif.setAttribute("Xdensity", dpi + "");
jfif.setAttribute("Ydensity", dpi + "");
jfif.setAttribute("resUnits", "1"); // density is dots per inch
ByteArrayOutputStream out = new ByteArrayOutputStream();
ImageOutputStream stream = null;
try {
stream = ImageIO.createImageOutputStream(out);
writer.setOutput(stream);
writer.write(data, new IIOImage(image, null, null), writeParams);
} finally {
stream.close();
}
return out.toByteArray();
}
return null;
}
@Override
public boolean canHandle(String fileName) {
assert fileName != null : "fileName should not be null";
return fileName.endsWith("jpg") || fileName.endsWith("jpeg") || fileName.endsWith("JPG")
|| fileName.endsWith("JPEG");
}
}
PNG处理方式：
public class PngDPIProcessor implements ImageDPIProcessor {
//1英寸是2.54里面
private static final double INCH_2_CM = 2.54d;
@Override
public boolean canHandle(String fileName) {
assert fileName != null : "fileName should not be null";
return fileName.endsWith("png") || fileName.endsWith("PNG");
}
@Override
public byte[] process(BufferedImage image, int dpi) throws MalformedURLException, IOException {
for (Iterator<ImageWriter> iw = ImageIO.getImageWritersByFormatName("png"); iw.hasNext();) {
ImageWriter writer = iw.next();
ImageWriteParam writeParam = writer.getDefaultWriteParam();
ImageTypeSpecifier typeSpecifier = ImageTypeSpecifier.createFromBufferedImageType(BufferedImage.TYPE_INT_RGB);
IIOMetadata metadata = writer.getDefaultImageMetadata(typeSpecifier, writeParam);
if (metadata.isReadOnly() || !metadata.isStandardMetadataFormatSupported()) {
continue;
}
ByteArrayOutputStream output = new ByteArrayOutputStream();
ImageOutputStream stream = null;
try {
setDPI(metadata, dpi);
stream = ImageIO.createImageOutputStream(output);
writer.setOutput(stream);
writer.write(metadata, new IIOImage(image, null, metadata), writeParam);
} finally {
try {
stream.close();
} catch (IOException e) {
}
}
return output.toByteArray();
}
return null;
}
private void setDPI(IIOMetadata metadata, int dpi) throws IIOInvalidTreeException {
// for PMG, it‘s dots per millimeter
double dotsPerMilli = 1.0 * dpi / 10 * INCH_2_CM;
IIOMetadataNode horiz = new IIOMetadataNode("HorizontalPixelSize");
horiz.setAttribute("value", Double.toString(dotsPerMilli));
IIOMetadataNode vert = new IIOMetadataNode("VerticalPixelSize");
vert.setAttribute("value", Double.toString(dotsPerMilli));
IIOMetadataNode dim = new IIOMetadataNode("Dimension");
dim.appendChild(horiz);
dim.appendChild(vert);
IIOMetadataNode root = new IIOMetadataNode("javax_imageio_1.0");
root.appendChild(dim);
metadata.mergeTree("javax_imageio_1.0", root);
}
}
原文：http://my.oschina.net/osgit/blog/530283