java设置图像dpi

 private BufferedImage gridImage;
  ...

  private void saveGridImage(File output) throws IOException {
     output.delete();

     final String formatName = "png";

     for (Iterator iw = ImageIO.getImageWritersByFormatName(formatName); 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;
        }

        setDPI(metadata);

        final ImageOutputStream stream = ImageIO.createImageOutputStream(output);
        try {
           writer.setOutput(stream);
           writer.write(metadata, new IIOImage(gridImage, null, metadata), writeParam);
        } finally {
           stream.close();
        }
        break;
     }
  }

  private void setDPI(IIOMetadata metadata) 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);
  }

 

 

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

其中DPI就是你要设置的值，java中默认是72，如果需要打印图片，可能就要设置为300

INCH_2_CM表示1英寸等于多少厘米，这里就是2.54