Java生成图片默认分辨率是72dpi,由于需要打印生成图片，要求图片分辨率至少300dpi,这个问题整了将近一天时间，最终得到解决，感谢网友的分享。在这里记录一下，已备后面使用。以下代码摘抄至https://my.oschina.net/osgit/blog/530283

/**

* 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;

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 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);

}

主要参考文章：

https://my.oschina.net/osgit/blog/530283

http://stackoverflow.com/questions/321736/how-to-set-dpi-information-in-an-image

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 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");

}

}