e699. compressing a jpeg file.txt

这里面包含了一百多个JAVA源文件

This example implements a method for writing a JPEG file with a specific compression quality. In J2SE 1.4, the compression capability is not functioning properly. This example demonstrates a workaround. 
    // Reads the jpeg image in infile, compresses the image,
    // and writes it back out to outfile.
    // compressionQuality ranges between 0 and 1,
    // 0-lowest, 1-highest.
    public void compressJpegFile(File infile, File outfile, float compressionQuality) {
        try {
            // Retrieve jpg image to be compressed
            RenderedImage rendImage = ImageIO.read(infile);
    
            // Find a jpeg writer
            ImageWriter writer = null;
            Iterator iter = ImageIO.getImageWritersByFormatName("jpg");
            if (iter.hasNext()) {
                writer = (ImageWriter)iter.next();
            }
    
            // Prepare output file
            ImageOutputStream ios = ImageIO.createImageOutputStream(outfile);
            writer.setOutput(ios);
    
            // Set the compression quality
            ImageWriteParam iwparam = new MyImageWriteParam();
            iwparam.setCompressionMode(ImageWriteParam.MODE_EXPLICIT) ;
            iwparam.setCompressionQuality(compressionQuality);
    
            // Write the image
            writer.write(null, new IIOImage(rendImage, null, null), iwparam);
    
            // Cleanup
            ios.flush();
            writer.dispose();
            ios.close();
        } catch (IOException e) {
        }
    }
    
    // This class overrides the setCompressionQuality() method to workaround
    // a problem in compressing JPEG images using the javax.imageio package.
    public class MyImageWriteParam extends JPEGImageWriteParam {
        public MyImageWriteParam() {
            super(Locale.getDefault());
        }
    
        // This method accepts quality levels between 0 (lowest) and 1 (highest) and simply converts
        // it to a range between 0 and 256; this is not a correct conversion algorithm.
        // However, a proper alternative is a lot more complicated.
        // This should do until the bug is fixed.
        public void setCompressionQuality(float quality) {
            if (quality < 0.0F || quality > 1.0F) {
                throw new IllegalArgumentException("Quality out-of-bounds!");
            }
            this.compressionQuality = 256 - (quality * 256);
        }
    }