Save (write) JPEG Images Without DPI Change in Java

If you try to write a BufferedImage on disk using ImageIO.write you will see that the result image will have a DPI of 96 regardless of the source image's DPI!
In order to keep the source DPI or set your own DPI you need to write your image using JPEGImageEncoder class.

      File inputFile = new File("source.jpg");
      File outputFile = new File("new.jpg");
      // create input buffered image
      BufferedImage image = ImageIO.read(inputFile);

      // create jpegEncode for output image
      JPEGImageEncoder jpegEncoder = JPEGCodec.createJPEGEncoder(new FileOutputStream(outputFile));

      // create jpeg encoder from getting defaul value from input buffered
      // image
      JPEGEncodeParam jpegEncodeParam = jpegEncoder.getDefaultJPEGEncodeParam(image);
      // setting up density unit paramter
      jpegEncodeParam.setDensityUnit(JPEGEncodeParam.DENSITY_UNIT_DOTS_INCH);
      // setting up jpeg encode parameter
      jpegEncoder.setJPEGEncodeParam(jpegEncodeParam);
      // set quality parameter
      jpegEncodeParam.setQuality(0.75f, false);
      // set X-resolution
      jpegEncodeParam.setXDensity(X_DPI);
      // set Y-resolution
      jpegEncodeParam.setYDensity(Y_DPI);
      // encode output image
      jpegEncoder.encode(image, jpegEncodeParam);
      // flush the buffer image
      image.flush();